Spatiotemporal trends in ground-level ozone concentrations and metrics in France over the time period 1999-2012

Assessment of ground-level ozone pollution in Türkiye according to new WHO limits

Ground-level ozone is a secondary pollutant and is attributable to respiratory diseases and mortality. For this reason, the World Health Organization (WHO) implemented a new long-term (peak season) limit value for ozone. The previous studies related to ozone in Türkiye were spatially limited to certain locations. In this study, annual mean and peak season ozone concentrations, and limit exceedances were investigated for Türkiye for the year 2021. Moreover, ozone peak seasons were determined for the first time for 126 air quality monitoring stations. The annual mean ozone concentration was determined as 44.3 ± 19.3 µg/m3 whereas the peak season average ozone level was 68.4 ± 27.2 µg/m3. April-September period was the most frequently observed ozone peak season. Among all stations, Erzurum Palandöken was by far the most polluted station in terms of annual mean and limit exceedances of ozone. Ankara Siteler stations have the highest rank in peak season mean. 87 and 83 stations exceeded the short-term and long-term recommendations of WHO, respectively. Four hotspot regions were revealed in terms of peak season exceedance: Adana and surrounding provinces, the surroundings of Burdur and Isparta provinces, and the northeastern and northwestern parts of Türkiye. To protect public health, WHO recommendations for 8-h and peak season limits should be immediately implemented in Turkish regulations.

Increased ground-level O3 during the COVID-19 pandemic in China aggravates human health risks but has little effect on winter wheat yield

In January 2020, the novel coronavirus (COVID-19) outbreak emerged in China, prompting the enforcement of stringent lockdown measures nationwide to contain its spread. Multiple studies have demonstrated that these measures successfully reduced the levels of air pollutants except for ozone (O3). However, the potential risks of nationwide O3 changes during this period remain uncertain. To address this gap, we evaluated the ecological and health effects of O3 using hourly O3 data from 1 January to 17 June in both 2020 and 2019. Our results indicated that all health and ecological indicators, except SUM06 (sum of all hourly O3 over 60 ppb), during the COVID-19 pandemic in 2020 increased most obviously in Stages 2 and 3 with the strictest control measures, compared to the same period in 2019. The national premature deaths due to short-term O3 exposure during Stages 2-3 in 2020 totaled 146,558 (95% CI: 79,386-213,730) for all non-accidental causes and 82,408 (95% CI: 30,522-134,295) for cardiovascular diseases, increasing by 18.78% and 18.76% in 2019, respectively. The most significant increase in health risks occurred in Hubei, followed by Jiangxi, Zhejiang, Hunan, and Shaanxi. In addition, the estimated national winter wheat production losses (WWPL) attributable to O3 amounted to 50.6 and 51.1 million metric tons for 2019 and 2020, respectively. Among the major winter wheat-producing provinces, Anhui and Jiangsu experienced a larger increase in WWPL, while Shandong and Hebei suffered a greater decrease in 2020 compared to 2019, resulting in little overall change in WWPL between the two years. These findings provided direct evidence of the harmful effects of O3 during the COVID-19 pandemic and serve as a valuable reference for future air pollution control.

Rebuilding high-quality near-surface ozone data based on the combination of WRF-Chem model with a machine learning method to better estimate its impact on crop yields in the Beijing-Tianjin-Hebei region from 2014 to 2019

In recent years, the problem of surface ozone pollution in China has been of great concern. According to observation data from monitoring stations, the concentration of near-surface ozone (O3) in China has gradually increased in recent years, and ozone concentration often exceeds the contaminant limit standard, especially in the Beijing-Tianjin-Hebei (BTH) region. High O3 concentration pollution will adversely affect crop growth, which can cause crop yield losses. Therefore, it is urgent to recognize the situation of ozone pollution in the BTH region and quantitatively evaluate the crop yield losses caused by ozone pollution to develop more effective pollution prevention and control policies. However, the monitoring of ozone concentration in China started relatively late compared with some developed countries, and currently, long-time series data covering the BTH region cannot be obtained, which makes it difficult to evaluate the impact of ozone on crop yield. Therefore, a new method (WRFC-XGB) was proposed in this study to establish a high-precision near-surface O3 concentration dataset covering the whole BTH region from 2014 to 2019 by integrating the Weather Research and Forecasting with Chemistry (WRF-Chem) model with the extreme gradient boosting (XGBoost) machine learning algorithm. Through verification with ground observation station data, the results of WRFC-XGB are satisfactory, and R2 can reach 0.78-0.91. Compared with other algorithms, the accuracy of the near-surface ozone concentration dataset is greatly improved, which can be used to estimate the impact of surface ozone on crop yield. Based on this dataset, the yield loss of winter wheat, rice, and maize caused by O3 pollution was estimated by using the response equation of the relative yield and ozone dose index. The results showed that the total yield losses of winter wheat, rice and maize from 2014 to 2019 were 2659.21 million tons, 49.23 million tons and 1721.56 million tons due to ozone pollution in the BTH region, respectively, and the highest relative yield loss of crops caused by O3 pollution could be 29.37% during 2014-2019, which indicated that the impact of ozone pollution on crop yield cannot be ignored, and effective measures need to be developed to control ozone pollution, prevent crop production loss, and ensure people's food security.

Effect of ozone stress on crop productivity: A threat to food security

Tropospheric ozone (O3), the most important phytotoxic air pollutant, can deteriorate crop quality and productivity. Notably, satellite and ground-level observations-based multimodel simulations demonstrate that the present and future predicted O3 exposures could threaten food security. Hence, the present study aims at reviewing the phytotoxicity caused by O3 pollution, which threatens the food security. The present review encompasses three major aspects; wherein the past and prevailing O3 concentrations in various regions were compiled at first, followed by discussing the physiological, biochemical and yield responses of economically important crop species, and considering the potential of O3 protectants to alleviate O3-induced phytotoxicity. Finally, the empirical data reported in the literature were quantitatively analysed to show that O3 causes detrimental effect on physiological traits, photosynthetic pigments, growth and yield attributes. The review on prevailing O3 concentrations over various regions, where economically important crop are grown, and their negative impact would support policy makers to implement air pollution regulations and the scientific community to develop countermeasures against O3 phytotoxicity for maintaining food security.

Significant land cover change in China during 2001-2019: Implications for direct and indirect effects on surface ozone concentration

China has become one of the most prominent areas of global land cover change during the past few decades. These changes can directly influence meteorological parameters thus further regulating tropospheric ozone (O3) formation. Moreover, changes in biogenic emissions due to land cover variation can also have an indirect effect on O3 concentration. This study applied the Community Multiscale Air Quality model to comprehensively evaluate the impacts of significant land cover change on O3 levels in China during summertime between 2001 and 2019. The results showed that the daily maximum 8-h average O3 concentration (MDA8 O3) increased by 3.6-8.9 μg/m3, 2.8-8.0 μg/m3, 3.8-9.6 μg/m3, -1.5-6.2 μg/m3, and -0.6-2.5 μg/m3 in Beijing-Tianjin-Hebei region, Yangtze River Delta, Pearl River Delta, Sichuan Basin, and Fenwei Plain, respectively, in response to land cover variation. The research identified that the direct effect was the primary factor in raising O3 levels which mainly altered O3 concentration by changing vertical import and dry deposition velocity. Moreover, land cover variation tended to decrease biogenic nitric oxide emission and increase biogenic volatile organic compounds emission on the whole, and cause an obvious increase of MDA8 O3 by 1.8-4.9 μg/m3 in Pearl River Delta due to the indirect effect. This study offered valuable insights into the impacts of land cover change on O3 levels, highlighting the need for policymakers to consider land cover variation on air pollutants concentration for devising comprehensive multi-pollutant control strategies.

Surface ozone risk to human health and vegetation in tropical region: The case of Thailand

Tropospheric ozone (O3) is a threat to vegetation and human health over the world, in particular in Asia. Knowledge on O3 impacts on tropical ecosystems is still very limited. An O3 risk assessment to crops, forests, and people from 25 monitoring stations across the tropical and subtropical Thailand during 2005-2018 showed that 44% of sites exceeded the critical levels (CLs) of SOMO35 (i.e., the annual Sum Of daily maximum 8-h Means Over 35 ppb) for human health protection. The concentration-based AOT40 CL (i.e., sum of the hourly exceedances above 40 ppb for daylight hours during the assumed growing season) was exceeded at 52% and 48% of the sites where the main crops rice and maize are present, respectively, and at 88% and 12% of the sites where evergreen or deciduous forests are present, respectively. The flux-based metric PODY (i.e., Phytotoxic Ozone Dose above a threshold Y of uptake) was calculated and was found to exceed the CLs at 1.0%, 1.5%, 20.0%, 1.5%, 0% and 68.0% of the sites where early rice, late rice, early maize, late maize, evergreen forests, and deciduous forests can grow, respectively. Trend analysis indicated that AOT40 increased over the study period (+5.9% year-1), while POD1 decreased (- 5.3% year-1), suggesting that the role of climate change in affecting the environmental factors that control stomatal uptake cannot be neglected. These results contribute novel knowledge on O3 threat to human health, forest productivity, and food security in tropical and subtropical areas.

A regional scale flux-based O3 risk assessment for winter wheat in northern Italy, and effects of different spatio-temporal resolutions

Tropospheric ozone (O3) is a secondary atmospheric pollutant known to cause negative effects on vegetation in terms of physiological oxidative stress, growth rate reductions and yield losses. In recent years, dose-response relationships based on the O3 stomatal flux and effects on the biomass growth have been defined for several crop species. This study was aimed at developing a dual-sink big-leaf model for winter wheat (Triticum aestivum L.) to map the seasonal Phytotoxic Ozone Dose above a threshold of 6nmolm-2s-1 (POD6) in a domain centered on the Lombardy region (Italy). The model runs on local measured data of air temperature, relative humidity, precipitation, wind speed, global radiation and background O3 concentration provided by regional monitoring networks, and includes parameterizations for the crop's geometry and phenology, the light penetration within the canopy, the stomatal conductance, the atmospheric turbulence, and the soil water availability for the plants. For the 2017 an average POD6 of 2.03mmolm-2PLA (Projected Leaf Area) was found for the Lombardy regional domain, corresponding to an average relative yield loss of 7.5%, using the finest spatio-temporal resolution (1×1km2 and 1-h). An analysis of the model's response to different spatio-temporal resolutions (from 2×2 to 50×50km2 and from 1 to 6 h) suggests that coarser resolution maps underestimated the average POD6 regional value from 8to16%, and were unable to detect O3 hotspots. Nevertheless, resolutions of 5×5km2 1-h, and 1×1km2 3-h, can still be considered reliable for the estimation of the O3 risk at the regional level since they presented relatively low root mean squared error. Furthermore, although temperature was the main limiting factor for the wheat stomatal conductance in most of the domain, soil water availability emerged as the key factor for determining the spatial patterns of the POD6.

Spatiotemporal variations of tropospheric ozone in Spain (2008-2019)

This study aims to support the development of Spain's Ozone Mitigation Plan by evaluating the present-day spatial variation (2015-2019) and trends (2008-2019) for seven ground-level ozone (O₃) metrics relevant for human/ecosystems exposure and regulatory purposes. Results indicate that the spatial variation of O₃ depends on the part of the O₃ distribution being analyzed. Metrics associated with moderate O₃ concentrations depict an increasing O₃ gradient between the northern and Mediterranean coasts due to climatic factors, while for metrics considering the upper end of the O₃ distribution, this climatic gradient tends to attenuate in favor of hotspot regions pointing to relevant local/regional O₃ formation. A classification of atmospheric regions in Spain is proposed based on their O₃ pollution patterns, to identify priority areas (or O₃ hotspots) where local/regional precursor abatement might significantly reduce O₃ during pollution episodes. The trends assessment reveals a narrowing of the O₃ distribution at the national level, with metrics influenced by lower concentrations tending to increase over time, and those reflecting the higher end of the O₃ distribution tending to decrease. While most stations show no statistically significant variations, contrasting O₃ trends are evident among the O₃ hotspots. The Madrid area exhibits the majority of upward trends across all metrics, frequently with the highest increasing rates, implying increasing O₃ associated with both chronic and episodic exposure. The Valencian Community area exhibits a mixed variation pattern, with moderate to high O₃ metrics increasing and peak metrics decreasing, while O₃ in areas downwind of Barcelona, the Guadalquivir Valley and Puertollano shows no variations. Sevilla is the only large Spanish city with generalized O₃ decreasing trends. The different O₃ trends among hotspots highlight the need for mitigation measures to be designed at a local/regional scale to be effective. This approach may offer valuable insights for other countries developing O₃ mitigation plans.

Spatialized temporal dynamics of daily ozone concentrations: Identification of the main spatial differences

Ground-level ozone (O₃) is one of the most worrisome air pollutants regarding environmental and health impacts. There is a need for a deeper understanding of its spatial and temporal dynamics. Models are needed to provide continuous temporal and spatial coverage in ozone concentration data with a fine resolution. However, the simultaneous influence of each determinant of ozone dynamics, their spatial and temporal variations, and their interaction make the resulting dynamics of O₃ concentrations difficult to understand. This study aimed to i) identify different classes of temporal dynamics of O₃ at daily and 9 km² resolution over a long-term period of 12 years, ii) identify the potential determinants of these dynamics and, iii) explore the spatial distribution of the potential classes of temporal dynamics on a spatial continuum and over about 1000 km². Thus, 126 time series of 12-year daily ozone concentrations were classified using dynamic time warping (DTW) and hierarchical clustering (study area centered on Besançon, eastern France). The different temporal dynamics obtained differed on elevation, ozone levels, proportions of urbanized and vegetated surfaces. We identified different daily ozone temporal dynamics, spatially structured, that overlapped areas called urban, suburban and rural. Urbanization, elevation and vegetation acted as determinants simultaneously. Individually, elevation and vegetated surface were positively correlated with O₃ concentrations (r = 0.84 and r = 0.41, respectively), while the proportion of urbanized area was negatively correlated with O₃ (r = -0.39). An increasing ozone concentration gradient was observed from urban to rural areas and was reinforced by the elevation gradient. Rural areas were both subject to higher ozone levels (p < 0.001), least monitoring and lower predictability. We identified main determinants of the temporal dynamics of ozone concentrations. The joint influence of determinants was also synthesized. This study proposed a systematic, and reproducible way to build exposure area mapping.

Urban Surface Ozone Concentration in Mainland China during 2015-2020: Spatial Clustering and Temporal Dynamics

Urban ozone (O₃) pollution in the atmosphere has become increasingly prominent on a national scale in mainland China, although the atmospheric particulate matter pollution has been significantly reduced in recent years. The clustering and dynamic variation characteristics of the O₃ concentrations in cities across the country, however, have not been accurately explored at relevant spatiotemporal scales. In this study, a standard deviational ellipse analysis and multiscale geographically weighted regression models were applied to explore the migration process and influencing factors of O₃ pollution based on measured data from urban monitoring sites in mainland China. The results suggested that the urban O₃ concentration in mainland China reached its peak in 2018, and the annual O₃ concentration reached 157 ± 27 μg/m³ from 2015 to 2020. On the scale of the whole Chinese mainland, the distribution of O₃ exhibited spatial dependence and aggregation. On the regional scale, the areas of high O₃ concentrations were mainly concentrated in Beijing-Tianjin-Hebei, Shandong, Jiangsu, Henan, and other regions. In addition, the standard deviation ellipse of the urban O₃ concentration covered the entire eastern part of mainland China. Overall, the geographic center of ozone pollution has a tendency to move to the south with the time variation. The interaction between sunshine hours and other factors (precipitation, NO₂, DEM, SO₂, PM_2.5) significantly affected the variation of urban O₃ concentration. In Southwest China, Northwest China, and Central China, the suppression effect of vegetation on local O₃ was more obvious than that in other regions. Therefore, this study clarified for the first time the migration path of the gravity center of the urban O₃ pollution and identified the key areas for the prevention and control of O₃ pollution in mainland China.

Trends in urban air pollution over the last two decades: A global perspective

Ground-level ozone (O₃), fine particles (PM_2.5), and nitrogen dioxide (NO₂) are the most harmful urban air pollutants regarding human health effects. Here, we aimed at assessing trends in concurrent exposure of global urban population to O₃, PM_2.5, and NO₂ between 2000 and 2019. PM_2.5, NO₂, and O₃ mean concentrations and summertime mean of the daily maximum 8-h values (O₃ MDA8) were analyzed (Mann-Kendall test) using data from a global reanalysis, covering 13,160 urban areas, and a ground-based monitoring network (Tropospheric Ozone Assessment Report), collating surface O₃ observations at nearly 10,000 stations worldwide. At global scale, PM_2.5 exposures declined slightly from 2000 to 2019 (on average, - 0.2 % year^-1), with 65 % of cities showing rising levels. Improvements were observed in the Eastern US, Europe, Southeast China, and Japan, while the Middle East, sub-Saharan Africa, and South Asia experienced increases. The annual NO₂ mean concentrations increased globally at 71 % of cities (on average, +0.4 % year^-1), with improvements in North America and Europe, and increases in exposures in sub-Saharan Africa, Middle East, and South Asia regions, in line with socioeconomic development. Global exposure of urban population to O₃ increased (on average, +0.8 % year^-1 at 89 % of stations), due to lower O₃ titration by NO. The summertime O₃ MDA8 rose at 74 % of cities worldwide (on average, +0.6 % year^-1), while a decline was observed in North America, Northern Europe, and Southeast China, due to the reduction in precursor emissions. The highest O₃ MDA8 increases (>3 % year^-1) occurred in Equatorial Africa, South Korea, and India. To reach air quality standards and mitigate outdoor air pollution effects, actions are urgently needed at all governance levels. More air quality monitors should be installed in cities, particularly in Africa, for improving risk and exposure assessments, concurrently with implementation of effective emission control policies that will consider regional socioeconomic imbalances.

Surface ozone trends at El Arenosillo observatory from a new perspective

Surface ozone trends observed at El Arenosillo observatory for the last 22 years (2000-2021) were investigated. The trends for daily averages and daily 5th and 95th percentiles were 1.2 ± 0.3 ppb decade^-1, 2.2 ± 0.3 ppb decade^-1 and -0.03 ± 0.43 ppb decade^-1, respectively, thus showing a significant increase of background ozone. The surface temperature trends were also explored, obtaining trends of 0.5 ± 0.2 ⁰C decade^-1, 1.1 ± 0.2 ⁰C decade^-1 and -0.3 ± 0.2 ⁰C decade^-1 for daily averages, 5th and 95th percentiles, respectively. To identify potential changes in the ozone drivers, the weather pattern shifts were analyzed through the horizontal distribution trends of temperature at 2 m and geopotential height at 850 hPa. A strengthening of the Azores anticyclone and a regional warming were detected, which could contribute to the ozone trends obtained. The surface ozone trend in every month was explored, identifying a monthly pattern, with remarkable opposite trends in December-January (2.4 ± 0.9 ppb decade^-1) vs July-August (-0.5 ± 1.1 ppb decade^-1). The surface ozone trends for every hour of the day were also explored, identifying two clear patterns. The first pattern occurred from spring to autumn and was characterized by a behavior opposite to the typical daily ozone cycle. The second pattern was observed in winter, and it shows two relative peaks in the ozone trends (around 13:00 and 19:00 UTC). In a context of ozone precursor's depletion, changes in the weather conditions and warmer climate, to improve our knowledge of the ozone trends, we suggest exploring them based on daily and hourly averages.

Sensitivity of agricultural crops to tropospheric ozone: a review of Indian researches

Tropospheric ozone (O₃) is a long-range transboundary secondary air pollutant, causing significant damage to agricultural crops worldwide. There are substantial spatial variations in O₃ concentration in different areas of India due to seasonal and geographical variations. The Indo-Gangetic Plain (IGP) region is one of the most crop productive and air-polluted regions in India. The concentration of tropospheric O₃ over the IGP is increasing by 6-7.2% per decade. The annual trend of increase is 0.4 ± 0.25% year^-1 over the Northeastern IGP. High O₃ concentrations were reported during the summer, while they were at their minimum during the monsoon months. To explore future potential impacts of O₃ on major crop plants, the responses of different crops grown under ambient and elevated O₃ concentrations were compared. The studies clearly showed that O₃ is an important stress factor, negatively affecting the yield of crops. In this review, we have discussed yield losses in agricultural crops due to rising O₃ pollution and variations in O₃ sensitivity among cultivars and species. The use of ethylene diurea (EDU) as a research tool in assessing the losses in yield under ambient and elevated O₃ levels also discussed. Besides, an overview of interactive effects of O₃ and nitrogen on crop productivity has been included. Several recommendations are made for future research and policy development on rising concentration of O₃ in India.

Spatiotemporal variations of ozone exposure and its risks to vegetation and human health in Cyprus: an analysis across a gradient of altitudes

Ground-level ozone (O₃) affects vegetation and threatens environmental health when levels exceed critical values, above which adverse effects are expected. Cyprus is expected to be a hotspot for O₃ concentrations due to its unique position in the eastern Mediterranean, receiving air masses from Europe, African, and Asian continents, and experiencing a warm Mediterranean climate. In Cyprus, the spatiotemporal features of O₃ are poorly understood and the potential risks for forest health have not been explored. We evaluated O₃ and nitrogen oxides (NO and NO₂) at four regional background stations at different altitudes over 2014-2016. O₃ risks to vegetation and human health were estimated by calculating accumulated O₃ exposure over a threshold of 40 nmol mol^-1 (AOT40) and cumulative exposure to mixing ratios above 35 nmol mol^-1 (SOMO35) indices. The data reveal that mean O₃ concentrations follow a seasonal pattern, with higher levels in spring (51.8 nmol mol^-1) and summer (53.2 nmol mol^-1) and lower levels in autumn (46.9 nmol mol^-1) and winter (43.3 nmol mol^-1). The highest mean O₃ exposure (59.5 nmol mol^-1) in summer occurred at the high elevation station Mt. Troodos (1819 m a.s.l.). Increasing (decreasing) altitudinal gradients were found for O₃ (NO_x), driven by summer-winter differences. The diurnal patterns of O₃ showed little variation. Only at the lowest altitude O₃ displayed a typical O₃ diurnal pattern, with hourly differences smaller than 15 nmol mol^-1. Accumulated O₃ exposures at all stations and in all years exceeded the European Union's limits for the protection of vegetation, with average values of 3-month (limit: 3000 nmol mol^-1 h) and 6-month (limit: 5000 nmol mol^-1 h) AOT40 for crops and forests of 16,564 and 31,836 nmol mol^-1 h, respectively. O₃ exposures were considerably high for human health, with an average SOMO35 value of 7270 nmol mol^-1 days across stations and years. The results indicate that O₃ is a major environmental and public health issue in Cyprus, and policies must be adopted to mitigate O₃ precursor emissions at local and regional scales.

Influence of Ozone and Drought on Tree Growth under Field Conditions in a 22 Year Time Series

Studying the effect of surface ozone (O3) and water stress on tree growth is important for planning sustainable forest management and forest ecology. In the present study, a 22-year long time series (1998–2019) on basal area increment (BAI) and fructification severity of European beech (Fagus sylvatica L.) and Norway spruce (Picea abies (L.) H.Karst.) at five forest sites in Western Germany (Rhineland Palatinate) was investigated to evaluate how it correlates with drought and stomatal O3 fluxes (PODY) with an hourly threshold of uptake (Y) to represent the detoxification capacity of trees (POD1, with Y = 1 nmol O3 m−2 s−1). Between 1998 and 2019, POD1 declined over time by on average 0.31 mmol m−2 year−1. The BAI showed no significant trend at all sites, except in Leisel where a slight decline was observed over time (−0.37 cm2 per year, p < 0.05). A random forest analysis showed that the soil water content and daytime O3 mean concentration were the best predictors of BAI at all sites. The highest mean score of fructification was observed during the dry years, while low level or no fructification was observed in most humid years. Combined effects of drought and O3 pollution mostly influence tree growth decline for European beech and Norway spruce.

Ozone modelling and mapping for risk assessment: An overview of different approaches for human and ecosystems health

Tropospheric ozone (O₃) is one of the most concernedair pollutants dueto its widespread impacts on land vegetated ecosystems and human health. Ozone is also the third greenhouse gas for radiative forcing. Consequently, it should be carefully and continuously monitored to estimate its potential adverse impacts especially inthose regions where concentrations are high. Continuous large-scale O₃ concentrations measurement is crucial but may be unfeasible because of economic and practical limitations; therefore, quantifying the real impact of O₃over large areas is currently an open challenge. Thus, one of the final objectives of O₃ modelling is to reproduce maps of continuous concentrations (both spatially and temporally) and risk assessment for human and ecosystem health. We here reviewedthe most relevant approaches used for O₃ modelling and mapping starting from the simplest geo-statistical approaches andincreasing in complexity up to simulations embedded into the global/regional circulation models and pro and cons of each mode are highlighted. The analysis showed that a simpler approach (mostly statistical models) is suitable for mappingO₃concentrationsat the local scale, where enough O₃concentration data are available. The associated error in mapping can be reduced by using more complex methodologies, based on co-variables. The models available at the regional or global level are used depending on the needed resolution and the domain where they are applied to. Increasing the resolution corresponds to an increase in the prediction but only up to a certain limit. However, with any approach, the ensemble models should be preferred.

Modeling Ground Ozone Concentration Changes after Variations in Precursor Emissions and Assessing Their Benefits in the Kanto Region of Japan

Ozone (O3) is a pollutant of concern in urban areas because of its effects on health, crops, ecosystems, and materials. Despite efforts to meet the Japanese air quality standard for O3 in the Kanto region, the attainment percentage is close to zero. Considering that O3 formation is sensitive to emissions of volatile organic compounds (VOC) and nitrogen oxides (NOx), this study evaluated a range of reductions in the emissions of both precursors using a regional air quality model (ADMER-PRO) and estimated their benefits measured as the economic change due to O3 concentration differences between scenarios. The simulation period was set during the 2016 O3 season. The results showed that O3 concentrations could be reduced using two approaches: significant reduction in VOC levels combined with minor NOx level changes or significant NOx emission reduction. Significant reduction in NOx levels was the most effective strategy for a generalized decrease in the O3 levels in the Kanto region, and the benefit analysis revealed that the most significant economic impacts could be achieved by adopting the latter approach.

Improvement of downscaled ozone concentrations from the transnational scale to the kilometric scale: Need, interest and new insights

BACKGROUND

Ground-level ozone is a major public health issue worldwide. An accurate assessment of ozone exposure is necessary. Modeling tools have been developed to tackle this issue in large areas. However, these models could present inaccuracies at the local scale.

OBJECTIVES

The objective of this study was i) to assess whether O₃ concentrations estimated by transnational modeling at the kilometric scale (9 km²) could be improved, ii) to propose a potential correction of these downscaled ozone concentrations and iii) to evaluate the efficiency and applicability of such a correction.

METHOD

The present work was carried out in three phases. First, the performance of a transnational modeling platform (PREV'EST) was assessed at 6 geographic points by comparison with data from 6 air quality monitoring stations. Performance indicators were used for this purpose (MBE (mean bias error), MAE (mean absolute error), RMSE (root mean square error), r (Pearson correlation coefficient), and target plots). Second, several corrections were developed using MARS (multivariate adaptive regression splines) and integrating different sets of variables (mean temperature, relative humidity, rainfall amount, wind speed, elevation, and date). Their performance was evaluated. Third, external validation of the corrections was conducted using the data from six additional air quality monitoring stations.

RESULTS

The uncorrected PREV'EST model presented a lack of exactitude and precision. These concentrations did not reproduce the interday variability of the measurements, leading to a lack of temporal contrast in exposure data. For the best performance enhancement, the correction applied improved MBE, MAE, RMSE and r from 14.67, 19.23, 23.18 and 0.67 to 0.00, 8.00, 10.19 and 0.91, respectively. External validation confirmed the efficiency of the corrections at the regional scale.

CONCLUSIONS

We propose a validated and efficient methodology integrating local environmental variables. The methodology is adaptable according to the context, needs and data available.

Gas-Phase Ozone Reaction Kinetics of C5-C8 Unsaturated Alcohols of Biogenic Interest

Unsaturated alcohols are volatile organic compounds (VOCs) that characterize the emissions of plants. Changes in climate together with related increases of biotic and abiotic stresses are expected to increase these emissions in the future. Ozonolysis is one of the oxidation pathways that control the fate of unsaturated alcohols in the atmosphere. The rate coefficients of the gas-phase O₃ reaction with seven C₅-C₈ unsaturated alcohols were determined at 296 K using both absolute and relative kinetic methods. The following rate coefficients (cm³ molecule^-1 s^-1) were obtained using the absolute method: (1.1 ± 0.2) × 10^-16 for cis-2-penten-1-ol, (1.2 ± 0.2) × 10^-16 for trans-2-hexen-1-ol, (6.4 ± 1.0) × 10^-17 for trans-3-hexen-1-ol, (5.8 ± 0.9) × 10^-17 for cis-3-hexen-1-ol, (2.0 ± 0.3) × 10^-17 for 1-octen-3-ol, and (8.4 ± 1.3) × 10^-17 for trans-2-octen-1-ol. The following rate coefficients (cm³ molecule^-1 s^-1) were obtained using the relative method: (1.27 ± 0.11) × 10^-16 for trans-2-hexen-1-ol, (5.01 ± 0.30) × 10^-17 for trans-3-hexen-1-ol, (4.13 ± 0.34) × 10^-17 for cis-3-hexen-1-ol, and (1.40 ± 0.12) × 10^-16 for trans-4-hexen-1-ol. Alkenols display high reactivities with ozone with lifetimes in the hour range. Rate coefficients show a strong and complex dependence on the structure of the alkenol, particularly the relative position of the OH group toward the C═C double bond. The results are discussed and compared to both the available literature data and four structure-activity relationship (SAR) methods.

Spatiotemporal characteristics of PM2.5 and ozone concentrations in Chinese urban clusters

Despite China's public commitment to emphasise air pollution investigation and control, trends in PM_2.5 and ozone concentrations in Chinese urban clusters remain unclear. This study quantifies the spatiotemporal variations in PM_2.5 and surface ozone at the scale of Chinese urban clusters by using a long-term integrated dataset from 2015 to 2020. Nonlinear Granger causality testing was used to explore the spatial association patterns of PM_2.5 and ozone pollution in five megacity cluster regions. The results show a significant downward trend in annual mean PM_2.5 concentrations from 2015 to 2020, with a decline rate of 2.8 μg m^-3 yr^-1. By contrast, surface ozone concentrations increased at a rate of 2.1 μg m^-3 yr^-1 over the 6 years. The annual mean PM_2.5 concentrations in urban clusters show significant spatial clustering characteristics, mainly in Beijing-Tianjin-Hebei (BTH), Fenwei Plain (FWP), Northern slope of Tianshan Mountains urban cluster (NSTM), Sichuan Basin urban cluster (SCB), and Yangtze River Delta (YRD). Surface ozone shows severe summertime pollution and distributional variability, with increased ozone pollution in major urban clusters. The highest increases were observed in BTH, Yangtze River midstream urban cluster (YRMR), YRD, and Pearl River Delta (PRD). Nonlinear Granger causality tests showed that PM_2.5 was a nonlinear Granger cause of ozone, further supporting the literature's findings that PM_2.5 reduction promoted photochemical reaction rates and stimulated ozone production. The nonlinear test statistic passed the significance test in magnitude and statistical significance. FWP was an exception, with no significant long-term nonlinear causal link between PM_2.5 and ozone. This study highlights the challenges of compounded air pollution caused primarily by ozone and secondary PM_2.5. These results have implications for the design of synergistic pollution abatement policies for coupled urban clusters.

Quantifying ecological and health risks of ground-level O3 across China during the implementation of the "Three-year Action Plan for Cleaner Air"

After China implemented the Air Pollution Prevention and Control Action Plan (APPCAP), PM_2.5 concentrations decreased but were still higher than national standards in major areas and ozone (O₃) concentration increased unintentionally. To further decrease PM_2.5 concentrations and reduce days with severe air pollution, the government promulgated the "Three-year (2018-2020) Action Plan for Cleaner Air" (the Three-year Action Plan) in 2018. During the three-year Action Plan, a few studies reported a continuous decline in PM_2.5, but it is unclear whether O₃ and its effects also increase with the decrease of PM_2.5 like during APPCAP. In this study, for the first time, we systematically assessed changes in ground-level O₃ concentrations and related ecological and health risks during the period of the Three-year Action Plan using nationwide O₃ measurements. The national MDA8, Exceedance, and SOMO35 indicators were reduced by 3.8%, 28.5%, and 12.6%, respectively, ecological risk indicators of M12, M7, SUM06, AOT40, and W126 were reduced by 5.4%, 5.6%, 19.5%, 15.4%, and 18.6%, respectively, from 2018 to 2020. Spatially, the greatest reduction in all the indicators except MDA8 occurred in Pearl River Delta, followed by Fen Wei Plains, while Beijing-Tianjin-Hebei, Chengdu-Chongqing, and Yangtze River Delta presented relatively small reductions. Between 2018 and 2020, the production losses caused by O₃ for wheat and rice decreased by 21.4% and 17.6%, respectively. Long-term exposure to O₃ across China over 2020 was estimated to cause about 160,795 (95% CI: 81,515-312,983) for all-cause mortality, 107,128 (95% CI: 36,703-173,823) for cardiovascular mortality, and 34,444 (95% CI: 0-72,609) for respiratory mortality, indicating decreases of 9.93%, 9.86%, and 9.78%, respectively, compared to the year 2018. Taken together, our results provided the first direct evidence for China's efforts to control O₃ pollution in recent years.

A Health Impact and Economic Loss Assessment of O3 and PM2.5 Exposure in China From 2015 to 2020

China is in a critical air quality management stage. Rapid industrial development and urbanization has resulted in non-ignorable air pollution, which seriously endangers human health. Assessment of the health impacts and economic losses of air pollution is essential for the prevention and control policy formulation. Based on ozone (O₃) and fine particulate matter concentration (PM_2.5) monitoring data in 331 Chinese cities from 2015 to 2020, this study evaluated the health effects and the corresponding economic losses of O₃ and PM_2.5 pollution on three health endpoints. The ratio of population exposed to O₃ levels that exceeded the Chinese Ambient Air Quality Standards (CAAQS) increased from 13.35% in 2015 to 14.15% in 2020, which resulted in 133,415 (2015) - 156,173 (2020) all-cause deaths, 88,941 (2015) - 104,051 (2020) cardiovascular deaths, and 28,614 (2015) - 33,456 (2020) respiratory deaths. The ratio of population exposed to PM_2.5 levels that exceeded the CAAQS decreased, but in many regions, especially in North China and the Yangtze River Delta, the PM_2.5 concentration remained high. By 2020, nearly half of the population in China was still exposed to PM_2.5 levels that exceeded the CAAQS, and the corresponding economic losses reached CNY 3.46 and 3.05 billion, respectively. These results improved the understanding of the spatial-temporal variation trends of major air pollutants at city scale in China, and emphasize the continued coordination urgently needed for controlling O₃ and PM_2.5 following the implementation of the 2013 policy to mitigate air pollution to protect human health.

Relationship between exposure to ozone and exacerbation requiring hospital admission among patients with asthma: a case-control study in central Taiwan

OBJECTIVE

The convergence of asthma and air pollutants in ageing populations is currently a growing health issue worldwide, and hence there is an essential need to investigate the association between exposure to air pollution, particularly ozone (O₃), and exacerbation requiring admission in patients with asthma.

SETTING

A case-control study at a tertiary referral hospital in central Taiwan.

PARTICIPANTS

We used an asthma cohort, which included 11 400 patients with asthma, for the period 2006-2018 at Taichung Veterans General Hospital.

PRIMARY AND SECONDARY OUTCOME MEASURES

We identified patients who had admitted for exacerbation as cases and selected patients with asthma without exacerbation, matching (1:4) the cases for age, gender and season of exacerbation, as controls. Data on hourly level of air pollutants were obtained from the Taiwan Environmental Protection Administration. We used conditional logistic regression and calculated adjusted ORs (adjORs) with 95% CIs.

RESULTS

We enrolled 11 400 participants with asthma, and 4.4% (501) of them had been admitted for exacerbation. Participants with asthma with exacerbation requiring hospitalisation were exposed to a higher level of O₃ 8-hour daily maximum (adjOR 1.009, 95% CI 1.001 to 1.016) and were more likely to have high Charlson Comorbidity Index (CCI ≥3; adjOR 2.198, 95% CI 1.729 to 2.794) and asthma-chronic obstructive pulmonary disease overlap (adjOR 4.542, 95% CI 3.376 to 6.611) compared with those without exacerbation. The aforementioned associations between exacerbation of asthma requiring hospitalisation and exposure to O₃ were similar when defined by either O₃ 1-hour daily maximum or O₃ 24-hour average. Moreover, the O₃ relevant exacerbation of asthma mainly existed in those aged older than 65 years and patients with medical comorbidities, including gastrointestinal diseases, cardiovascular diseases, neurological diseases, diabetes and renal disease.

CONCLUSIONS

Our findings highlight the need for vigilance of exposure to O₃ among elderly with asthma, particularly those with medical comorbidities. Further studies are warranted to investigate the underlying mechanisms.

Ozone pollution threatens the production of major staple crops in East Asia

East Asia is a hotspot of surface ozone (O₃) pollution, which hinders crop growth and reduces yields. Here, we assess the relative yield loss in rice, wheat and maize due to O₃ by combining O₃ elevation experiments across Asia and air monitoring at about 3,000 locations in China, Japan and Korea. China shows the highest relative yield loss at 33%, 23% and 9% for wheat, rice and maize, respectively. The relative yield loss is much greater in hybrid than inbred rice, being close to that for wheat. Total O₃-induced annual loss of crop production is estimated at US$63 billion. The large impact of O₃ on crop production urges us to take mitigation action for O₃ emission control and adaptive agronomic measures against the rising surface O₃ levels across East Asia.

Assessment of ozone risk to Central European forests: Time series indicates perennial exceedance of ozone critical levels

In this study, the stomatal ozone (O₃) fluxes were investigated at five low-elevation forest sites in Western Germany (Rhineland Palatinate) over the time period 1998-2019. The Phytotoxic Ozone Dose with an hourly threshold of uptake (Y), to represent the detoxification capacity of trees (POD1 in mmol m^-2 per leaf area, with Y = 1 nmol O₃ m^-2 s^-1), and the number of exceedances of the O₃ critical level of 5.2 mmol O₃ m^-2 per leaf area for European beech and 9.2 mmol O₃ m^-2 per leaf area for Norway spruce were calculated by using the DO₃SE model. A Principal Component Analysis revealed strong correlations between daily O₃ concentrations, daytime O₃ (for hours with global radiation exceeding 50 W m^-2), POD1, global radiation, vapor pressure deficit and air temperature. Moreover, a significant correlation was obtained between POD1 and soil water content (SWC) at all sites (r = 0.51-0.74). The Random Forests Analysis confirmed that the SWC is the most important predictor of stomatal O₃ fluxes. The soil water supply is very important for POD1 estimation, because drought decreases stomatal conductance, leading to a reduction of transpiration, as well as to lower O₃ uptake through stomata. Between 1998 and 2019, the drier and warmer climate induced a soil drought (on average, SWC - 0.15 % per year) leading to lower stomatal O₃ uptake by forests (- 0.36 mmol O₃ m^-2 per year). Hence, during growing seasons with sufficient water supply and often lower O₃ levels compared to hot and dry periods, forests are at higher O₃ risk than during hot and dry periods when the drought stress is more significant than O₃ stress despite relatively higher O₃ levels. Irrespective of these differences in O₃ uptake between relatively cool and humid as compared to relatively hot and dry years in the study region, the Critical Level for O₃ was exceeded in late spring/early summer (May/June) during all 22 years. Risk assessment for the protection of European forests, which is urgently needed due to the forests current critical state after several successive years of drought and exceedance of the O₃ critical level in large areas of Europe, should therefore become flux-based to account for the inter-twined effects of drought and O₃ on the physiology and health of forest trees in the region. For stomatal O₃ fluxes estimation, a better soil water and leaf parameterization is needed e.g., by taking into account both O₃- and drought-induced effects.

A machine learning model to estimate ground-level ozone concentrations in California using TROPOMI data and high-resolution meteorology

Estimating ground-level ozone concentrations is crucial to study the adverse health effects of ozone exposure and better understand the impacts of ground-level ozone on biodiversity and vegetation. However, few studies have attempted to use satellite retrieved ozone as an indicator given their low sensitivity in the boundary layer. Using the Troposphere Monitoring Instrument (TROPOMI)'s total ozone column together with the ozone profile information retrieved by the Ozone Monitoring Instrument (OMI), as TROPOMI ozone profile product has not been released, we developed a machine learning model to estimate daily maximum 8-hour average ground-level ozone concentration at 10 km spatial resolution in California. In addition to satellite parameters, we included meteorological fields from the High-Resolution Rapid Refresh (HRRR) system at 3 km resolution and land-use information as predictors. Our model achieved an overall 10-fold cross-validation (CV) R² of 0.84 with root mean square error (RMSE) of 0.0059 ppm, indicating a good agreement between model predictions and observations. Model predictions showed that the suburb of Los Angeles Metropolitan area had the highest ozone levels, while the Bay Area and the Pacific coast had the lowest. High ozone levels are also seen in Southern California and along the east side of the Central Valley. TROPOMI data improved the estimate of extreme values when compared to a similar model without it. Our study demonstrates the feasibility and value of using TROPOMI data in the spatiotemporal characterization of ground-level ozone concentration.

A 10-year assessment of ambient fine particles and related health endpoints in a large Mediterranean city

Fine particles i.e., with an aerodynamic diameter lower than 2.5 μm (PM_2.5) have potentially the most significant effects on human health compared to other air pollutants. The main objectives of this study were to i) investigate the temporal variations of ambient PM_2.5 in Marseille (Southern France), where air pollution is again a major public health issue, and ii) estimate their short-term health effects and annual trend (Mann-Kendall test) over a 10-year period from 2010 to 2019. In Marseille, the main sources of PM_2.5 could be related to road traffic, industrial complexes, and oil refineries surrounded the city. The number of premature deaths and hospital admissions attributable to ambient PM_2.5 exposure for non-accidental causes, cardiovascular and respiratory diseases were estimated by using in-situ air quality data, city-specific relative risk values and baseline incidence. Despite significant reduction of PM_2.5 (- 0.80 μg m^-3 year^-1), Marseille citizens were exposed to PM_2.5 levels exceeding the World Health Organization (WHO) Air Quality Guideline for human health protection (10 μg m^-3) during entire study period. Exposure to ambient PM_2.5 substantially contributed to mortality and hospital admissions: 871 deaths for non-accidental causes, 515 deaths for cardiovascular diseases, 47 deaths for respiratory diseases, as well as 1034 hospital admissions for cardiovascular diseases and 834 for respiratory diseases were reported between 2010 and 2019. Compliance with WHO annual limit values can result in substantial socio-economic benefits by preventing premature deaths and hospital admissions. For instance, based on the value of a statistical life and average cost of a hospital admission, the associated benefit for healthcare would have been €131 million in 2019. Between 2010 and 2019, the number of PM_2.5-related non-accidental deaths decreased by 1.15 per 10⁵ inhabitants annually. Compared to 2010-2019, the restrictive measures associated to COVID-19 pandemic led to a reduction in PM_2.5 of 11% in Marseille, with 2.6 PM_2.5-related deaths averted in 2020.

On the investigation of COVID-19 lockdown influence on air pollution concentration: regional investigation over eighteen provinces in Iraq

At the end of 2019, a novel coronavirus COVID-19 emerged in Wuhan, China, and later spread throughout the world, including Iraq. To control the rapid dispersion of the virus, Iraq, like other countries, has imposed national lockdown measures, such as social distancing, restriction of automobile traffic, and industrial enterprises. This has led to reduced human activities and air pollutant emissions, which caused improvement in air quality. This study focused on the analysis of the impact of the six partial, total, and post-lockdown periods (1st partial lockdown from March 1 to16, 2020, 1st total lockdown from March 17 to April 21, 2nd partial lockdown from April 22 to May 23, 2nd total lockdown from May 24 to June 13, 3rd partial lockdown from June 14 to August 19, and end partial lockdown from August 20 to 31) on the average of daily NO₂, O₃, PM_2.5, and PM₁₀ concentrations, as well as air quality index (AQI) in 18 Iraqi provinces during these periods (from March 1st to August 31st, 2020). The analysis showed a decline in the average of daily PM_2.5, PM₁₀, and NO₂ concentrations by 24%, 15%, and 8%, respectively from March 17 to April 21, 2020 (first phase of total lockdown) in comparison to the 1st phase of partial lockdown (March 1 to March 16, 2020). Furthermore, the O₃ increased by 10% over the same period. The 2nd phase of total lockdown, the 3rd partial lockdown, and the post-lockdown periods witnessed declines in PM_2.5 by 8%, 11%, and 21%, respectively, while the PM₁₀ increases over the same period. Iraqi also witnessed improvement in the AQI by 8% during the 1st phase of total lockdown compared to the 1st phase of partial lockdown. The level of air pollutants in Iraq declined significantly during the six lockdown periods as a result of reduced human activities. This study gives confidence that when strict measures are implemented, air quality can improve.

Impact of ground-level ozone on Mediterranean forest ecosystems health

Given the high ozone concentrations observed in the Mediterranean region during summer, it is crucial to extend our knowledge on the potential ozone impacts on forest health with in situ studies, especially to protect typical endemic forests of the Mediterranean basin. This study is focused on ozone measurements and exposures over the Eastern Adriatic coast and on the calculation of different O₃ metrics, i.e., accumulated exposure AOT40 (AOT40_dir, AOT40_ICP, AOT40_pheno) and stomatal O₃ fluxes with an hourly threshold of uptake (Y) to represent the detoxification capacity of trees (PODY, with Y = 0, 1, 2 nmol O₃ m^-2 s^-1) used for forest protection. Finally, we provide an assessment of the relationships between the forest response indicators and environmental variables. Passive ozone measurements and monitoring of forest health indicators, namely growth and crown defoliation, were performed for Quercus ilex, Quercus pubescens, Pinus halepensis, and Pinus nigra forests. Results showed that, for all the analysed species, ozone levels were close to reached the upper plausibility limits for passive monitoring of air quality at forest sites (100 ppb), with the highest values found on P. halepensis in the summer period. O₃ metrics based on exposure were found to be higher in pine plots than in oak plots, while the highest values of uptake-based metrics were found on P. nigra. Regarding relationships between environmental variables and forest-health response indicators, the crown defoliation was significantly correlated with the soil water content at various depth while the tree growth was correlated with the different O₃ metrics. The most important predictors affecting tree growth of Q. pubescens and Q. ilex were AOT40_pheno and AOT40_dir and POD0 for P. nigra.

Simulation of average monthly ozone exposure concentrations in China: A temporal and spatial estimation method

BACKGROUND

Ozone has adverse effects on human health, it is necessary to obtain the refined ozone exposure concentration. At present, most of existing ozone exposure research is based on ground air quality monitoring station (MS) which gather urban area information only. It is diffcult to estimate the ozone in the areas where MSs are scarce.

OBJECTIVE

By combining accurate but uneven data of outdoor ozone exposure concentrations based on MSs and unbiased coverage data based on RS in China, we can improve the accuracy of simulation of average monthly ozone exposure concentrations in monitor-free area. Since ozone concentrations are usually low at night, ozone exposure is assessed during the day (e.g., 10:00-18:00).

METHODS

We proposed a space-time geostatistical kriging interpolation based on the composite space/time mean trend model (CSTM) to predict ozone exposure in mainland China, having obtained a refined ozone exposure concentration interpolation map from an MS. We verified the accuracy of the interpolation results and remote sensing (RS) data, while simultaneously determining the distance threshold (according to the data accuracy) to improve the accuracy of the hybrid map.

RESULTS

We used a refined smoothing filter to reduce the influence of spatial and seasonal trends on ozone concentration. We found a cutoff separation distance of 175 km at which the two data showed an equal estimation accuracy, and the estimation result was fused with RS data through the distance threshold. Finally, The multi-source data with the best accuracy were fused to obtain the refined map. In China, ozone exposure concentration mainly gathers in the northern and eastern regions as well as part of the central mainland.

CONCLUSIONS

RS data can be used to characterize ground ozone exposure concentrations when 24th-layer data and MS data for monitoring ozone exposure concentrations are combined to estimate temporal and spatial ozone exposure in China. Ozone exposure in China can be explored further to provide suggestions for human health and regional economic development.

Coordinated control of PM2.5 and O3 is urgently needed in China after implementation of the "Air pollution prevention and control action plan"

To improve air quality, China formulated the Air Pollution Prevention and Control Action Plan (APPCAP) in 2013. In the present study, the changes in the concentration of air pollutants after the implementation of APPCAP were investigated based on nationwide monitoring data. From the results, it is evident that the annual mean concentrations of PM_2.5, PM₁₀, SO₂, and CO show a significant downward trend over 2015-2018, with decreasing rates of 3.4, 4.1, 3.8, and 70 μg m^-3/year, respectively. However, no significant change was found in NO₂ while maximum daily 8 h average O₃ concentration (MDA8 O₃) was increased by 3.4 μg m^-3/year during the four years. Spatially, the highest decrease in PM_2.5 was found in Beijing-Tianjin-Hebei (BTH), followed by central China and northeast China, while the Pearl River Delta (PRD), Yungui Plateau, and northwest China showed less decreases. MDA8 O₃ had a higher increase in BTH, central China, Yangtze River Delta (YRD), and PRD. With the decrease in PM_2.5 in recent years, cumulative population exposure to PM_2.5 gradually decreased, whereas there was still more than 65% of the population exposing to annual PM_2.5 higher than the standard of 35 μg m^-3 in 2018. In contrast, the health effects of O₃ gradually increased with 13.1%, 14.3%, 20.4%, and 21.7% of the population exposed to unhealthy O₃ levels in summer from 2015 to 2018. O₃ pollution is causing severe health risks with estimated nationwide mortality of 70,024 (95% CI: 55,510-84,501), 79,159 (95% CI: 62,750-95,525), 105,150 (95% CI: 83,378-126,852), and 104,404 (95% CI: 82,784-125,956) in the four years, respectively. This clearly shows that the target of air pollution control in China shifts and coordinated control of PM_2.5 and O₃ is urgently needed after the successful implementation of APPCAP.

Ozone Concentration Levels in Urban Environments-Upper Silesia Region Case Study

Although ozone (O₃) plays a crucial role in screening the Earth’s surface and lower atmosphere layers from the ultraviolet radiation, troposphere ozone is proven to have negative health effects on the human body and is one of the greenhouse gases. The objective of this study was to perform a measurement-based assessment for determining whether the concentration of ozone is within admissible limits, or exceeded, in Silesia Province and does not pose a threat to the local population. The data provided by the Voivodship Inspectorate for Environmental Protection in Katowice were used in the analysis. The received data constitute the result of 8-h measurements of concentrations of ozone at selected air monitoring stations of the Silesian province. The locations of three monitoring stations were found to be useful for the aim of this research; one site is situated in a rural background area; another one is located in a medium-sized city and the Katowice station is representative for an urban background situation. We used cluster analysis, weighted pair group method using arithmetic averages (WPGMA) and Chebyshev distances to test the hypothesis and compare empirical distributions in the general population. The alarm level has not been exceeded in indicated measurements stations in Silesian Voivodship in the period 2015–2017 (averaging time 1 h: 240 µg/m³ for 3 h). The target level was exceeded in 2015 at all three measurements stations and in the following years at one station (in Zloty Potok, 2016, and in Katowice, 2017). Each year, the largest number of exceedances occurred in August. The results clearly indicate a lack of hazards for the general population’s health in terms of increased concentrations of ozone in the city centers and outside. The results confirm that environmental conditions (i.e., landform, the area surrounding monitoring station) have a significant influence on the ozone level.

Urban population exposure to air pollution in Europe over the last decades

BACKGROUND

The paper presents an overview of air quality in the 27 member countries of the European Union (EU) and the United Kingdom (previous EU-28), from 2000 to 2017. We reviewed the progress made towards meeting the air quality standards established by the EU Ambient Air Quality Directives (European Council Directive 2008/50/EC) and the World Health Organization (WHO) Air Quality Guidelines by estimating the trends (Mann-Kendal test) in national emissions of main air pollutants, urban population exposure to air pollution, and in mortality related to exposure to ambient fine particles (PM_2.5) and tropospheric ozone (O₃).

RESULTS

Despite significant reductions of emissions (e.g., sulfur oxides: ~ 80%, nitrogen oxides: ~ 46%, non-methane volatile organic compounds: ~ 44%, particulate matters with a diameter lower than 2.5 µm and 10 µm: ~ 30%), the EU-28 urban population was exposed to PM_2.5 and O₃ levels widely exceeding the WHO limit values for the protection of human health. Between 2000 and 2017, the annual PM_2.5-related number of deaths decreased (- 4.85 per 10⁶ inhabitants) in line with a reduction of PM_2.5 levels observed at urban air quality monitoring stations. The rising O₃ levels became a major public health issue in the EU-28 cities where the annual O₃-related number of premature deaths increased (+ 0.55 deaths per 10⁶ inhabitants).

CONCLUSIONS

To achieve the objectives of the Ambient Air Quality Directives and mitigate air pollution impacts, actions need to be urgently taken at all governance levels. In this context, greening and re-naturing cities and the implementation of fresh air corridors can help meet air quality standards, but also answer to social needs, as recently highlighted by the COVID-19 lockdowns.

Human, Forest and vegetation health metrics of ground-level ozone (SOMO35, AOT40f and AOT40v) in Tehran

PURPOSE

We aimed to investigate the spatial O₃ indices (SOMO35: annual sum of maximum daily 8-h ozone means over 35 ppb, AOT40: the accumulated exposure over an hourly threshold of 40 ppb during daylight hours between 8:00 and 20:00 in the growing seasons of plants) in Tehran (2019-2020).

METHODS

The data of ambient O₃ concentrations, measured at twenty-three regulatory ambient air quality monitoring stations (AQMSs) in Tehran, were obtained.

RESULTS

The annual mean O₃ concentrations were found to be 15.8-25.7 ppb; the highest and lowest annual mean concentration of ambient O₃ were observed in Shahrdari 22 and Shahr-e-Rey stations, respectively. Spatial distribution of exposure to O₃ across Tehran was in the range of 1.36-1.64; the highest O₃ concentrations were observed in the northern, west and south-western parts of Tehran, while the central and south areas of Tehran city experienced low to moderate concentrations. The indices of SOMO35, AOT40f and AOT40v across AQMSs in Tehran was in the range of 1830-6437 ppb. Days, 10,613-39,505 ppb.h and 4979-16,804 ppb.h, respectively. For Tehran city, the indices of SOMO35 and AOT40f were 4138 ppb. days and 27,556 ppb.h respectively. Our results revealed that the value of SOMO35 across AQMSs of Tehran was higher than the recommended target value of 3000 ppb. days.

CONCLUSIONS

To reduce O₃ pollution and its effects on both human and plants health, the governmental organizations should take appropriate sustainable control policies.

Ozone weekend effect in cities: Deep insights for urban air pollution control

Studying weekend-weekday variation in ground-level ozone (O₃) allows one to better understand O₃ formation conditions, with a potential for developing effective strategies for O₃ control. Reducing inappropriately the O₃ precursors emissions can either produce no reduction or increase surface O₃ concentrations. This paper analyzes the weekend-weekday differences of O₃ at 300 rural and 808 urban background stations worldwide from 2005 to 2014, in order to investigate the O₃ weekend effect over time and assess the effectiveness of the precursors emissions control policies for reducing O₃ levels. Data were analyzed with the non-parametric Mann-Kendall test and Theil-Sen estimator. Rural sites typically did not experience a weekend-weekday effect. In all urban stations, the mean O₃ concentration on the weekend was 12% higher than on weekdays. Between 2005 and 2014, the annual mean of daily O₃ concentrations increased at 74% of urban sites worldwide (+ 0.41 ppb year^-1) and decreased in the United Kingdom (- 0.18 ppb year^-1). Over this time period, emissions of O₃ precursors declined significantly. However, a greater decline in nitrogen oxides (NO_x) emissions caused an increase in Volatile Organic Compounds (VOCs) to NO_x ratios leading to O₃ formation. In France, South Korea and the United Kingdom, most urban stations showed a significant upward trend (+ 1.15% per year) for O₃ weekend effect. Conversely, in Canada, Germany, Japan, Italy and the United States, the O₃ weekend effect showed a significant downward trend (- 0.26% per year). Further or inappropriate control of anthropogenic emissions in Canada, Southern Europe, Japan, South Korea and the United States might result in increased daily O₃ levels in urban areas.

Evaluating the effects of ground-level O3 on rice yield and economic losses in Southern China

Ground-level ozone (O₃) pollution and its impact on crop growth and yield have become one of the serious environmental problems in recent years, especially in economically active and densely populated areas. In this study, rice yield and the associated economic losses due to O₃ were estimated by using observational O₃ concentration ([O₃]) data during growing seasons in Southern China. O₃-induced yield losses were calculated by using O₃ exposure metrics of AOT40 and M7. The spatial distribution of these two metrics is relatively consistent, the highest areas located in the Yangtze River Basin. Under the current O₃ level, during double-early rice, double-late rice and single rice growing seasons, the relative yield losses estimated with AOT40 (M7) were 6.8% (1.2%), 10.2% (1.9%) and 10.4% (2.0%), respectively. O₃-induced rice production loss for double-early rice, double-late rice and single rice totaled 2.4 million metric tons (0.4 million metric tons), 4.3 million metric tons (0.7 million metric tons) and 11.0 million metric tons (1.9 million metric tons) and associated economic losses were 108.1 million USD (18.3 million USD), 190.2 million USD (32.4 million USD) and 486.4 million USD (82.9 million USD) based on AOT40 (M7) metric. This study indicates that regional risks to rice from O₃ exposure and provide quantitative evidence of O₃-induced impacts on rice yields and economic losses across Southern China. Therefore, the establishment of scientific O₃ risk assessment method is of great significance to prevent yield production and economic losses caused by O₃ exposure. Policymakers should strengthen supervision of emissions of O₃ precursors to mitigate the rise of O₃ concentration, thereby reducing O₃ damage to agricultural production.

Yield and economic losses of winter wheat and rice due to ozone in the Yangtze River Delta during 2014-2019

Ground-level ozone (O₃) is the main phytotoxic air pollutant causing crop yield reduction in China. As the main grain producing area in China, the Yangtze River Delta (YRD) is facing serious O₃ pollution. This study analyzed the hourly ground-level O₃ observation data of 158 stations from 2014 to 2019 in YRD, and grain production data of 193 districts and counties. The exposure-response relationships based on AOT40 (accumulated hourly O₃ concentration above 40 ppb) was used to estimate the yield loss and economic loss of two food crops (winter wheat and rice). This study used spatial interpolation and calculated the specific data values of each district and county in order to improve the assessment reliability. For years 2014-2019, averaged O₃ concentration during the 75 days growing period of rice and wheat were 33.1-50.6 ppb and 32.2-48.0 ppb, AOT40 value were 5.2-12.0 ppm h and 4.6-9.4 ppm h, and the averaged relative yield losses were 4.9%-11.4% and 9.4%-19.3%, respectively. The trend of O₃ in the YRD in a six-year period peaked in 2016 and 2017 for rice and winter wheat, respectively. During 2014-2017, the average estimated yield loss of rice was 2445 Mt. accounting for about 9.1% of the actual production, and the average estimated economic loss was about 1037 million USD; for winter wheat, it was 2025 Mt, 20.4% and 736 million USD, respectively. These results urge governments to provide effective policies and measures to control O₃ pollution.

Ionic Strength Effect Alters the Heterogeneous Ozone Oxidation of Methoxyphenols in Going from Cloud Droplets to Aerosol Deliquescent Particles

Methoxyphenols are one of the most abundant classes of biomarker tracers for atmospheric wood smoke pollution. The reactions of atmospheric oxidants (ozone, OH) with methoxyphenols can contribute to the formation of secondary organic aerosols (SOA). Here, for the first time, we use the well-established vertical wetted wall flow tube (VWWFT) reactor to assess the effect of ionic strength (I), pH, temperature, and ozone concentration on the reaction kinetics of ozone with acetosyringone (ACS), as a representative methoxyphenol compound. At fixed pH 3, typical for acidic atmospheric deliquescent particles, and at I = 0.9 M adjusted by Na₂SO₄, the uptake coefficient (γ) of O₃ increases by 2 orders of magnitude from γ = (5.0 ± 0.8) × 10^-8 on neat salt solution (Na₂SO₄) to γ = (6.0 ± 0.01) × 10^-6 on a mixture of ACS and Na₂SO₄. The comparison of the uptake coefficients of O₃ at different pH values indicates that the reaction kinetics strongly depends on the acidity of the phenolic group of ACS. The observed different reactivity of gas-phase ozone with ACS has implications for ozone uptake by the dilute aqueous phase of cloud droplets and by aerosol deliquescent particles loaded with inorganic salts, and it can affect the formation of SOA in the atmosphere.

Amplified ozone pollution in cities during the COVID-19 lockdown

The effect of lockdown due to coronavirus disease (COVID-19) pandemic on air pollution in four Southern European cities (Nice, Rome, Valencia and Turin) and Wuhan (China) was quantified, with a focus on ozone (O₃). Compared to the same period in 2017-2019, the daily O₃ mean concentrations increased at urban stations by 24% in Nice, 14% in Rome, 27% in Turin, 2.4% in Valencia and 36% in Wuhan during the lockdown in 2020. This increase in O₃ concentrations is mainly explained by an unprecedented reduction in NO_x emissions leading to a lower O₃ titration by NO. Strong reductions in NO₂ mean concentrations were observed in all European cities, ~53% at urban stations, comparable to Wuhan (57%), and ~65% at traffic stations. NO declined even further, ~63% at urban stations and ~78% at traffic stations in Europe. Reductions in PM_2.5 and PM₁₀ at urban stations were overall much smaller both in magnitude and relative change in Europe (~8%) than in Wuhan (~42%). The PM reductions due to limiting transportation and fuel combustion in institutional and commercial buildings were partly offset by increases of PM emissions from the activities at home in some of the cities. The NO_x concentrations during the lockdown were on average 49% lower than those at weekends of the previous years in all cities. The lockdown effect on O₃ production was ~10% higher than the weekend effect in Southern Europe and 38% higher in Wuhan, while for PM the lockdown had the same effect as weekends in Southern Europe (~6% of difference). This study highlights the challenge of reducing the formation of secondary pollutants such as O₃ even with strict measures to control primary pollutant emissions. These results are relevant for designing abatement policies of urban pollution.

Pollution zone identification research during ozone pollution processes

Identifying an ozone pollution zone during the pollution processes is significant for ozone pollution management and environmental health risk assessment. However, few studies have focused on ozone pollution zone identification during pollution processes. A spatial-temporal clustering framework for identifying pollution zones during ozone pollution processes was initially proposed in this study, and an ozone pollution process in China in May 2017 was selected as a case. The results showed that the framework can help selecting one more accurate method to identify the pollution zone according to the pollution characteristics of air pollution process. In addition, different ozone pollution zone identification methods work well in different scenarios: The self-organizing map (SOM) method was suitable for identifying the zone with the duration of pollution between 24 and 48 h, the image fusion based on wavelet transform (IFbWT) method for the zone with the duration of pollution over 48 h and the Apriori method for the zone with obvious boundaries between high-value and low-value ozone concentrations. The proposed procedure can also be applied to identify the pollution zone of the pollution process of other pollutants.

Ozone affects plant, insect, and soil microbial communities: A threat to terrestrial ecosystems and biodiversity

Elevated tropospheric ozone concentrations induce adverse effects in plants. We reviewed how ozone affects (i) the composition and diversity of plant communities by affecting key physiological traits; (ii) foliar chemistry and the emission of volatiles, thereby affecting plant-plant competition, plant-insect interactions, and the composition of insect communities; and (iii) plant-soil-microbe interactions and the composition of soil communities by disrupting plant litterfall and altering root exudation, soil enzymatic activities, decomposition, and nutrient cycling. The community composition of soil microbes is consequently changed, and alpha diversity is often reduced. The effects depend on the environment and vary across space and time. We suggest that Atlantic islands in the Northern Hemisphere, the Mediterranean Basin, equatorial Africa, Ethiopia, the Indian coastline, the Himalayan region, southern Asia, and Japan have high endemic richness at high ozone risk by 2100.

Ozone Trends in the United Kingdom over the Last 30 Years

Previous work regarding the behaviour of ozone surface concentrations over many years in the United Kingdom had predicted that the frequency and severity of ozone episodes would become less marked in the future as a response to environmental regulations. The aim of this study is to extend these studies and compare the results with their predictions. The ozone data of 13 rural and six urban sites in the UK collected from the Department for Environment, Food and Rural Affairs over a period from 1992 to mid-2019 were used to investigate this behaviour. The yearly ozone exceedances (the number of hours that the ozone concentration exceeded the 50 ppbv limit) in the United Kingdom were found to have decreased over the last 30 years regardless of the type of site (rural or urban), showing that the adopted emission controls have so far been successful in the abatement of pollutant emissions. In the past three decades, the highest numbers of exceedances were reached in May regardless of the type of site. Furthermore, these episodes have become less frequent and less severe in recent years. In fact, the number of hours of exceedance is lower than that in previous decades, and it is almost constant throughout the week.

Modifiers of the effect of short-term variation in PM2.5 on mortality in Beijing, China

INTRODUCTION

Epidemiologic studies have reported associations between short-term exposure to particulate matter <2.5 μm in aerodynamic diameter (PM_2.5) and mortality, but the role of modifiers remains unclear with studies reporting inconsistent results. We evaluated the impact of individual (age, gender and education) and township (geographic area, socioeconomic status, background air pollution and road density) level factors on the relationship between short-term variation in PM_2.5 with cause-specific mortality in Beijing (population: 21.7 million in 2016), China.

METHODS

Daily PM_2.5 concentrations in each township (n = 327; township population: 2000-359,400; township area: 1-392 km²) within Beijing were estimated by kriging with external drift using measurements from 35 air quality monitoring stations and geographic variables. Time-stratified case-crossover analysis with township-level mortality data from Oct. 1st, 2012 to Dec. 31st, 2013 was then used to examine associations between PM_2.5 exposure estimates and cause-specific mortality, stratified by the potential effect modifiers.

RESULTS

A 10-μg/m³ increase in PM_2.5 concentration was associated with a 0.17% [95% confidence interval (CI): 0.05%-0.29%] and 0.27% (95%CI:0.01%-0.52%) increase in non-accidental and stroke mortality with no lag, a 0.81% (95%CI:0.39%-1.23%) and 0.96% (95%CI:0.35%-1.57%) increase in respiratory disease (RD) and chronic obstructive pulmonary disease (COPD) mortality at a lag of two-day moving average. For individual-level effect modifiers, the elderly showed higher effects for all the specific causes of mortality; those with lower education level showed higher effects for non-accidental, cardiovascular disease and stroke mortality; females showed higher effects for non-accidental and cause-specific cardiovascular diseases. For township-level effect modifiers, effect estimates tended to be larger for suburban areas, areas of lower road density, lower PM_2.5 and lower socioeconomic status.

CONCLUSIONS

Short-term exposure to township-level ambient PM_2.5 was associated with increased mortality in Beijing, with indications of effect modification by both individual and township-level factors.

Health impact assessment by the implementation of Madrid City air-quality plan in 2020

OBJECTIVES

Air pollutant concentrations in many urban areas are still above the legal and recommended limits that are set to protect the citizens' health. Madrid is one of the cities where traffic causes high NO₂ levels. In this context, Madrid City Council launched the Air Quality and Climate Change Plan for the city of Madrid (Plan A), a local strategy approved by the previous government in 2017. The aim of this study was to conduct a quantitative health impact assessment to evaluate the number of premature deaths that could potentially be prevented by the implementation of Plan A in Madrid in 2020, at both citywide and within-city level. The main purpose was to support decision-making processes in order to maximize the positive health impacts from the implementation of Plan A measures.

METHODS

The Regional Statistical Office provided information on population and daily mortality in Madrid. For exposure assessment, we estimated PM_2.5, NO₂ and O₃ concentration levels for Madrid city in 2012 (baseline air-quality scenario) and 2020 (projected air-quality scenario based on the implementation of Plan A), by means of an Eulerian chemical-transport model with a spatial resolution of 1 km × 1 km and 30 vertical levels. We used the concentration-response functions proposed by two relevant WHO projects to calculate the number of attributable annual deaths corresponding to all non-accidental causes (ICD-10: A00-R99) among all-ages and the adult population (>30 years old) for each district and for Madrid city overall. This health impact assessment was conducted dependant on health-data availability.

RESULTS

In 2020, the implementation of Plan A would imply a reduction in the Madrid citywide annual mean PM_2.5 concentration of 0.6 μg/m³ and 4.0 μg/m³ for NO₂. In contrast, an increase of 1 μg/m³ for O₃ would be expected. The annual number of all-cause deaths from long-term exposure (95% CI) that could be postponed in the adult population by the expected air-pollutant concentration reduction was 88 (57-117) for PM_2.5 and 519 (295-750) for NO₂; short-term exposure accounted for 20 (7-32) for PM_2.5 and 79 (47-111) for NO₂ in the total population. According to the spatial distribution of air pollutants, the highest mortality change estimations were for the city centre - including Madrid Central and mainly within the M-30 ring road -, as compared to peripheral districts. The positive health impacts from the reductions in PM_2.5 and NO₂ far exceeded the adverse mortality effects expected from the increase in O₃.

CONCLUSIONS

Effective implementation of Plan A measures in Madrid city would bring about an appreciable decline in traffic-related air-pollutant concentrations and, in turn, would lead to significant health-related benefits.

Evaluating the effects of surface O3 on three main food crops across China during 2015-2018

In order to tackle China's severe air pollution issue, the government has released the "Air Pollution Prevention and Control Action Plan" (known simply as the "Action Plan") since 2013. A recent study reported a decreased trend in PM_2.5 concentrations over 2013-2017, but O₃ pollution has become more serious. However, the effects of surface O₃ on crops are unclear after the implementation of the "Action Plan". Here, we evaluated the potential negative effects of surface O₃ on three main food crops (winter wheat, maize and rice) across China during 2015-2018 using nationwide O₃ monitoring data and AOT40-yield response functions. Results suggested that mean O₃ concentration, AOT40 and relative yield loss in China showed an overall upward trend from 2015 to 2018. During winter wheat, maize, single rice, double-early rice, and double-late rice growing seasons, mean O₃ concentration in recent years ranged from 38.6 to 46.9 ppb, 40.2-43.9 ppb, 39.3-42.2 ppb, 33.8-40.0 ppb, and 35.9-39.1 ppb, respectively, and AOT40 mean values ranged from 8.5 to 14.3 ppm h, 10.5-13.4 ppm h, 9.8-11.9 ppm h, 5.2-9.2 ppm h, and 8.0-9.5 ppm h, respectively. O₃-induced yield reductions were estimated to range from 20.1 to 33.3% for winter wheat, 5.0-6.3% for maize, 7.3-8.8% for single rice, 3.9-6.8% for double-early rice and 5.9-7.1% for double-late rice. O₃-induced production losses for winter wheat, maize, single rice, double-early rice, and double-late rice totaled 39.5-88.2 million metric tons, 12.6-21.0 million metric tons, 9.5-11.3 million metric tons, 1.2-1.8 million metric tons, and 2.2-2.7 million metric tons, respectively, and the corresponding economic losses totaled 14.3-32.0 billion US$, 3.9-6.5 billion US$, 3.9-4.6 billion US$, 0.5-0.7 billion US$, and 0.9-1.1 billion US$, respectively. Our results suggested that the government should take effective measures to reduce O₃ pollution and its effects on agricultural production.

Temporal variations of ambient air pollutants and meteorological influences on their concentrations in Tehran during 2012-2017

We investigated temporal variations of ambient air pollutants and the influences of meteorological parameters on their concentrations using a robust method; convergent cross mapping; in Tehran (2012–2017). Tehran citizens were consistently exposed to annual PM_2.5, PM₁₀ and NO₂ approximately 3.0–4.5, 3.5–4.5 and 1.5–2.5 times higher than the World Health Organization air quality guideline levels during the period. Except for O₃, all air pollutants demonstrated the lowest and highest concentrations in summertime and wintertime, respectively. The highest O₃ concentrations were found on weekend (weekend effect), whereas other ambient air pollutants had statistically significant (P < 0.05) daily variations in which higher concentrations were observed on weekdays compared to weekend (holiday effect). Hourly O₃ concentration reached its peak at 3.00 p.m., though other air pollutants displayed two peaks; morning and late night. Approximately 45% to 65% of AQI values were in the subcategory of unhealthy for sensitive groups and PM_2.5 was the responsible air pollutant in Tehran. Amongst meteorological factors, temperature was the key influencing factor for PM_2.5 and PM₁₀ concentrations, while nebulosity and solar radiation exerted major influences on ambient SO₂ and O₃ concentrations. Additionally, there is a moderate coupling between wind speed and NO₂ and CO concentrations.

Trend analysis of surface ozone at suburban Guangzhou, China

The long-term variations of ozone are the combined results of climate change and air quality management. As Guangzhou is under the influence of both subtropical monsoon climate and rapid economic development, the ozone trend in recent years is uncertain. This paper presents the trend analysis of maximum daily average 8 h (MDA8) ozone and daily meteorological observations in Guangzhou from 2008 to 2018, using the Kolmogorov-Zurbenko (KZ) filter method. The observations were conducted at two sites in suburban Guangzhou, thus the datasets were processed in two periods. The first period (P1) is from 2008 to 2013, and the second period (P2) is from 2014 to 2018. Results show that the KZ filter method separates the short-term, seasonal, and long-term components efficiently, leaving a covariance term of 7.3% (5.4%) for P1 (P2). Through linear regression of long-term components, the trends were inferred as -0.06 ± 0.04 ppb year^-1 (R² = 0.00, p < 0.05) for P1, and 0.51 ± 0.08 ppb year^-1 (R² = 0.11, p < 0.05) for P2. It is found that the solar radiation has the strongest impact on ozone. With inclusion of temperature, relative humidity, and wind speed, these four meteorological factors held 71% (76%) variability in baseline ozone (sum of seasonal and long-term ozone) for P1 (P2). After applying the KZ filter method, the results reveal that the variance contribution of emission to long-term ozone variation is larger than that of meteorology in P1, while smaller in P2. Furthermore, 59% of the emission-induced ozone change in P2 could be explained by nitrogen dioxide variation, and their inverse correlation suggests that Guangzhou is mainly under volatile organic compounds-limited regime, despite continuous nitrogen oxides reduction.

Urban aerobiological risk mapping of ornamental trees using a new index based on LiDAR and Kriging: A case study of plane trees

Ornamental trees bring benefits for human health, including reducing urban pollution. However, some species, such as plane trees (Platanus sp.), produce allergenic pollen. Consequently, urban maps are a valuable tool for allergic patients and allergists, but they often fail to include variables that contribute to the "building downwash effect", such as the width and shape of streets and the height of buildings. Other factors that directly influence pollen dispersion (slopes and other geographical features) also have not traditionally been discussed. The LiDAR (Laser Imaging Detection and Ranging) technique enables one to consider these variables with high accuracy. This work proposes an Aerobiological Index to create Risk maps for Ornamental Trees (AIROT) and the establishment of potential areas of risk of exposure to Platanus pollen. LiDAR data from five urban areas were used to create the DEM and DSM (Digital Elevation and Surface Models) needed to perform further analysis. GIS software was used to map the points for each city and to create risk maps by Kriging, with stable (3 cases) and exponential function (2 cases) as the optimal models. In short, the AIROT index was a useful tool to map possible biological risks in cities. Since AIROT allows each city to consider its own characteristics, including geographical specifications, by using remote sensing and geostatistics techniques, the establishment of risk maps and healthy itineraries is valuable for allergic patients, allergists, architects and urban planners. This new aerobiological index provides a new decision-making tool related to urban planning and allergenicity assessment.

Toward stomatal-flux based forest protection against ozone: The MOTTLES approach

European standards for the protection of forests from ozone (O₃) are based on atmospheric exposure (AOT40) that is not always representative of O₃ effects since it is not a proxy of gas uptake through stomata (stomatal flux). MOTTLES "MOnitoring ozone injury for seTTing new critical LEvelS" is a LIFE project aimed at establishing a permanent network of forest sites based on active O₃ monitoring at remote areas at high and medium risk of O₃ injury, in order to define new standards based on stomatal flux, i.e. POD_Y (Phytotoxic Ozone Dose above a threshold Y of uptake). Based on the first year of data collected at MOTTLES sites, we describe the MOTTLES monitoring station, together with protocols and metric calculation methods. AOT40 and POD_Y, computed with different methods, are then compared and correlated with forest-health indicators (radial growth, crown defoliation, visible foliar O₃ injury). For the year 2017, the average AOT40 calculated according to the European Directive was even 5 times (on average 1.7 times) the European legislative standard for the protection of forests. When the metrics were calculated according to the European protocols (EU Directive 2008/50/EC or Modelling and Mapping Manual LTRAP Convention), the values were well correlated to those obtained on the basis of the real duration of the growing season (i.e. MOTTLES method) and were thus representative of the actual exposure/flux. AOT40 showed opposite direction relative to PODY. Visible foliar O₃ injury appeared as the best forest-health indicator for O₃ under field conditions and was more frequently detected at forest edge than inside the forest. The present work may help the set-up of further long-term forest monitoring sites dedicated to O₃ assessment in forests, especially because flux-based assessments are recommended as part of monitoring air pollution impacts on ecosystems in the revised EU National Emissions Ceilings Directive.

Effect of O3, PM10 and PM2.5 on cardiovascular and respiratory diseases in cities of France, Iran and Italy

At present, both tropospheric ozone (O₃) and particulate matters (PM) are among the most threatening air pollutants for human health in cities. The air pollution effects over public health include increased risk of hospital admissions and mortality for respiratory and cardiovascular diseases even when air pollutant concentrations are below European and international standards. The aim of this study was to (i) estimate the burden of mortality and morbidity for cardiovascular and respiratory diseases attributed to PM_2.5, PM₁₀ and O₃ in nine selected cities in France, Iran and Italy in 2015 and 2016 and to (ii) compare estimated burdens at current O₃ and PM levels with pre-industrial levels. The selected Mediterranean cities are among the most affected by the air pollution in Europe, in particular by rising O₃ while the selected Iranian cities rank as the most polluted by PM in the world. The software AirQ+ was used to estimate the short-term health effects, in terms of mortality and morbidity by using in situ air quality data, city-specific relative risk values and baseline incidence. Compared to pre-industrial levels, long-term exposures to ambient PM_2.5, PM₁₀ and O₃ have substantially contributed to mortality and hospital admissions in selected cities: about 8200 deaths for non-accidental causes, 2400 deaths for cardiovascular diseases, 540 deaths for respiratory diseases, 220 deaths for chronic obstructive pulmonary diseases as well as 18,800 hospital admissions for cardiovascular diseases and 3400 for respiratory diseases were reported in 2015. The study supports the need of city-specific epidemiological data and urgent strategies to mitigate the health burden of air pollution.