Temporal Changes in Ozone Concentrations and Their Impact on Vegetation

Structured Cerium-Manganese Catalysts Supported on Nickel Foam for Toluene Oxidation by Electric Internal Heating

Structured catalysts are widely used in catalytic oxidation of gaseous pollutants, hot catalysis is usually needed to assist the reaction in the catalytic process. Herein, a Ce-modified manganese oxide octahedral molecular sieves (Ce-OMS-2) structured catalyst supported on foam nickel was prepared through impregnation process. A systematically quantitative testing on the toluene catalytic oxidation effectiveness of this structured catalyst was conducted through catalyst evaluation device, combining a series of characterization methods, such as XRD and SEM, the structure-activity relationship was established. Assisted with electric internal heating and ozone oxidation environments, this structured catalyst exhibits excellent catalytic oxidation performance for oxidative decomposition of toluene even under high humidity conditions. The results showed that the ozone-coupled structured nickel foam catalyst increased the decomposition efficiency of toluene from 25 % (without catalyst and heating) to 55 % (with catalyst and without heating) and the electric internal heating can significantly improve the reactivity and moisture resistance of the structured nickel-foam catalyst, at 90 % RH and 40000 h-1, 50000 ppb O3 and 40 mg/m3 toluene was maintained 100 % catalytic efficiency. The high-efficiency non-precious metal-based electrothermal catalyst prepared herein is expected to have certain enlightenment for the purification of VOCs.

Addressing ozone pollution to promote United Nations sustainable development goal 2: Ensuring global food security

Achieving global food security and ensuring sustainable agriculture, the dual objectives of the second Sustainable Development Goal (SDG 2), necessitate immediate and collaborative efforts from developing and developed nations. The adverse effects of ozone on crop yields have the potential to significantly undermine the United Nations' ambitious target of attaining food security and ending hunger by 2030. This review examines the causes of growing tropospheric ozone, especially in India and China which lead to a substantial reduction in crop yield and forest biomass. The findings show that a nexus of high population, rapid urbanization and regional pollution sources aggravates the problem in these countries. It elucidates that when plants are exposed to ozone, specific cellular pathways are triggered, resulting in changes in the expression of genes related to hormone production, antioxidant metabolism, respiration, and photosynthesis. Assessing the risks associated with ozone exposure involves using response functions that link exposure-based and flux-based measurements to variables like crop yield. Precisely quantifying the losses in yield and economic value in food crops due to current ozone levels is of utmost importance in comprehending the risks ozone poses to global food security. We conclude that policymakers should focus on implementing measures to decrease the emissions of ozone precursors, such as enhancing vehicle fuel efficiency standards and promoting the use of cleaner energy sources. Additionally, efforts should be directed toward mapping or developing crop varieties that can tolerate ozone, applying protective measures at critical stages of plant growth and establishing ozone-related vegetation protection standards.

Ozone exposure induces metabolic stress and olfactory memory disturbance in honey bees

Human activities, urbanization, and industrialization contribute to pollution that affects climate and air quality. A main atmospheric pollutant, the tropospheric ozone (O3), can damage living organisms by generating oxidative radicals, causing respiratory problems in humans and reducing yields and growth in plants. Exposure to high concentrations of O3 can result in oxidative stress in plants and animals, eventually leading to substantial ecological consequences. Plants produce volatile organic compounds (VOCs) emitted in the environment and detected by pollinators (mainly by their antennae), foraging for nutritious resources. Several pollinators, including honey bees, recognize and discriminate flowers through olfactory cues and memory. Exposure to different concentrations of O3 was shown to alter the emission of floral VOCs by plants as well as their lifetime in the atmosphere, potentially impacting plant-pollinator interactions. In this report, we assessed the impacts of exposure to field-realistic concentrations of O3 on honey bees' antennal response to floral VOCs, on their olfactory recall and discriminative capacity and on their antioxidant responses. Antennal activity is altered depending on VOCs structure and O3 concentrations. During the behavioral tests, we first check consistency between olfactory learning rates and memory scores after 15 min. Then bees exposed to 120 and 200 ppb of ozone do not exert specific recall responses with rewarded VOCs 90 min after learning, compared to controls whose specific recall responses were consistent between time points. We also report for the first time in honey bees how the superoxide dismutase enzyme, an antioxidant defense against oxidative stress, saw its enzymatic activity rate decreases after exposure to 80 ppb of ozone. This work tends to demonstrate how hurtful can be the impact of air pollutants upon pollinators themselves and how this type of pollution needs to be addressed in future studies aiming at characterizing plant-insect interactions more accurately.

Effects of Fireworks Burning on Air Quality during the Chinese Spring Festival-Evidence from Zhengzhou, China

Fireworks burning significantly degrades air quality over a short duration. The prohibition of fireworks burning (POFB) policy of 2016 and the restricted-hours fireworks burning (RHFB) policy of 2023 in Zhengzhou City provide an ideal opportunity to investigate the effects of such policies and of fireworks burning on air quality during the Spring Festival period. Based on air quality ground-based monitoring data and meteorological data for Zhengzhou City, the article analyzes the impact of the POFB policy and the RHFB policy on air quality. The results show that: (1) The ban on fireworks burning significantly affects Spring Festival air quality, with a decrease of 16.0% in the Air Quality Index (AQI) value in 2016 compared to 2015 and a 74.9% increase in 2023 compared to 2022. (2) From 2016 to 2022, the Spring Festival period witnessed a substantial decrease in average concentration of main pollutants, along with a delayed occurrence of peak concentrations, indicating a noticeable "peak-shaving" effect. However, in 2023, there was an increase in pollutant concentrations, volatility, and a significant surge in hourly concentration. (3) The POFB policy and RHFB policy notably impacted PM2.5 and PM10, with a decrease of 16.1% and 23.6% in PM2.5 and PM10 concentrations, respectively, in 2016 compared to 2015, but an increase of 74.5% and 79.2%, respectively, in 2023 compared to 2022. (4) The contribution of fireworks burning to PM2.5 concentrations significantly decreased during the fireworks burning period (FBP) in 2016 after the POFB policy and increased significantly in 2023 during FBP after the implementation of the RHFB policy. Unfavorable meteorological conditions will undoubtedly exacerbate air quality pollution caused by fireworks burning.

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.

Ambient ozone at a rural Central European site and its vertical concentration gradient close to the ground

The representativeness of ambient air quality of an in situ measurement is key in the use and correct interpretation of the measured concentration values. Though the horizontal representativeness aspect is generally not neglected in air pollution studies, a detailed, high-resolution vertical distribution of ambient air pollutant concentrations is rarely addressed. The aim of this study is twofold: (i) to explore the vertical distribution of ground-level ozone (O3) concentrations measured at four heights above the ground-namely at 2, 8, 50, and 230 m-and (ii) to examine in detail the vertical O3 concentration gradient in air columns between 2 and 8, 8 and 50, and 50 and 230 m above the ground. We use the daily mean O3 concentrations measured continuously at the Košetice station, representing the rural Central European background ambient air quality observed during 2015-2021. We use the semiparametric GAM (generalised additive model) approach (with complexity or roughness-penalised splines implementation) to analyse the data with sufficient flexibility. Our models for both O3 concentrations and O3 gradients use (additive) decomposition into annual trend and seasonality (plus an overall intercept). The seasonal and year-to-year patterns of the modelled O3 concentrations look very similar at first glance. Nevertheless, a more detailed look through O3 gradients shows that they differ substantially with respect to their seasonal and long-term dynamics. The vertical O3 concentration gradient in 2-230 m is not uniform but changes substantially with increasing height and shows by far the highest dynamics near the ground between 2 and 8 m, differing in both the seasonal and annual aspects for all the air columns inspected. We speculate that non-linear changes of both seasonal and annual components of vertical O3 gradients are due to atmospheric-terrestrial interactions and to meteorological factors, which we will explore in a future study.

Silicic and Ascorbic Acid Induced Modulations in Photosynthetic, Mineral Uptake, and Yield Attributes of Mung Bean (Vigna radiata L. Wilczek) under Ozone Stress

Most of the world's crop production and plant growth are anticipated to be seriously threatened by the increasing tropospheric ozone (O₃) levels. The current study demonstrates how different mung bean genotypes reacted to the elevated level of O₃ in the presence of exogenous ascorbic and silicic acid treatments. It is the first report to outline the potential protective effects of ascorbic and silicic acid applications against O₃ toxicity in 12 mung bean {Vigna radiata (L.) Wilken} varieties. Under controlled circumstances, the present investigation was conducted in a glass house. There were four different treatments used: control (ambient O₃ concentration of 40-45 ppb), elevated O₃ (120 ppb), elevated O₃ with silicic acid (0.1 mM), and elevated O₃ with ascorbic acid (10 mM). Three varieties, viz. NM 20-21, NM 2006, and NM 2016, showcased tolerance to O₃ toxicity. Our findings showed that ascorbic and silicic acid applications gradually increased yield characteristics such as seed yield, harvest index, days to maturity, and characteristics related to gas exchange such as transpiration rate, stomatal conductance, net photosynthetic activity, and water-use efficiency. Compared to the control, applying both growth regulators enhanced the mineral uptake across all treatments. Based on the findings of the current study, it is concluded that the subject mung bean genotypes responded to silicic acid treatment more efficiently than ascorbic acid to mitigate the harmful effects of O₃ stress.

Air quality assessment in biosphere reserves close to emission sources. The case of the Spanish "Tablas de Daimiel" national park

This work shows that biosphere reserves, national parks and other protected natural areas require in situ tools to monitor and detect local and remote air pollution sources which are a threat to flora, fauna water and soil. Industries in surrounding areas, traffic and long-range transport of air pollution, can change with time and meteorology and so each national park should also have a historical database of the air quality in the site. This study reports surface measurements of ozone, NO, NO₂, CO, SO₂ and PM_2.5 acquired from March 2020 to July 2021 in "Las Tablas de Daimiel", a wetland Mediterranean National Park bordered by different cities and new industries in the field of the revalorization of agricultural wastes. Simultaneous data from a background station in a rural area isolated from air pollution are considered as reference. Twelve campaigns of one week duration were also performed to sample air in sorbent tubes to analyse volatile organic compounds from anthropogenic sources. Data are discussed considering meteorology, especially wind speed and direction together with the assessment of back-trajectories of air masses from distant sources. The results show that the effects of pollution from local and faraway sources on air quality in the park were weak. Thus, except for the high levels of ozone, with a mean value of 71 μg.m^-3, measured mass loadings for pollutants were low and not in exceedance of the air quality standards. Saharan dust events were frequent and contributed to PM_2.5 levels in the site. NO_x and SO₂ average concentrations (3.2 and 0.4 μg.m^-3, respectively) were below the recommended critical levels for vegetation and all the quantified VOCs were found in average concentration levels below 0.5 μg.m^-3.

Low sensitivity of Pinus mugo to surface ozone pollution in the subalpine zone of continental Europe

High altitudes have been exposed to enhanced levels of surface ozone (O₃) concentrations over recent decades compared to the pre-industrial era. The responses of vegetation to this toxic pollutant are species-specific and depend on the climate conditions. In this paper, we explored the reaction of Pinus mugo (P. mugo) to O₃-induced stress in the continental climate of an ozone-rich mountain area in the High Tatra Mountains (Western Carpathians). The effects of O₃ doses modelled by a deposition model, O₃ concentrations and other factors on P. mugo were identified from (a) satellite-based data via NDVI (normalised differenced vegetation index) over 2000-2020 and (b) visible injury on needle samples gathered from P. mugo individuals at ground-truth sites in 2019 and 2020. Analysing the NDVI trend, we observed non-significant changes (p > 0.05) in the greenness of P. mugo despite growing in an environment with the average seasonal O₃ concentration around 51.6 ppbv, the maximum hourly concentrations more than 90 ppbv and increasing trend of O₃ doses by 0.1 mmol m^-2 PLA (plant leaf area) year^-1. The visible O₃ injury of samples collected at study sites was low (mean injury observed on 1-10% of needles' surface), and the symptoms of injury caused by other biotic and abiotic factors prevailed over those caused by O₃. In addition, the correlation analyses between NDVI and the climatic factors indicated a significant (p < 0.05) and positive relationship with photosynthetic active radiation (R = 0.45) in July, and with stomatal conductance (R = 0.52) and temperature factor (R = 0.43) in August. Therefore, we concluded that the positive effect of climate conditions, which support the growth processes of P. mugo, may suppress the negative effect of the mean O₃ doses of 17.8 mmol m^-2 PLA accumulated over the growing season.

The ground-level ozone concentration in forest and urban environments in central Slovakia

This paper analyses data by summarising the concentration values of ground-level ozone (GLO). The study area is situated in central Slovakia and is part of the Western Carpathians. These measurements were carried out between 2015 and 2020, implementing Werner's method working with passive samplers. The highest average and the highest absolute GLO deposition values were 30.93 ppb and 61.06 ppb, respectively, recorded in August 2015 in the forest in the Kremnické vrchy Mts. The lowest average GLO value in the whole measuring period was 17.72 ppb, measured in the town of Zvolen; the absolute minimum was 4.43 ppb, recorded in April 2016 on an open plot in the Kremnické vrchy Mts. The GLO formation over the study area has not yet reached a steady rate. Since 2007, the developmental trend has been increasing. Statistically significant differences in GLO concentrations were confirmed between the localities with different airborne pollutions. However, the analysis of the existing ozone concentration values showed considerable differences, especially related to the time pattern. The spatial variability was equalised. The extreme values, while remarkable, were dangerous, especially in the forest stands in the Kremnické vrchy Mts., where they were 14 times above the critical level of 32.5 ppb O₃. The dominant factor influencing the GLO concentration was global radiation. The effects of average temperature and rainfall total were less important.

Regeneration of Pinus sibirica Du Tour in the Mountain Tundra of the Northern Urals against the Background of Climate Warming

Climate is one of the key drivers of the plant community’s structure and trends. However, the regional vegetation-climate features in the ecotone have not yet been sufficiently studied. The aim of the research is to study features of Pinus sibirica Du Tour germination, survival, and growth in the mountain tundra of the Northern Urals against the background of a changing climate. The following research objectives were set: To determine the abundance and age structure of P. sibirica undergrowth on the mountain tundra plateau, identify the features of P. sibirica growth in the mountain tundra, and examine the correlation between the multi-year air temperature pattern, precipitation, and P. sibirica seedling emergence. A detailed study of the Pinus sibirica natural regeneration in the mountain stony shrub-moss-lichen tundra area at an altitude of 1010–1040 m above sea level on the Tri Bugra mountain massif plateau (59°30′ N, 59°15′ E) in the Northern Urals (Russia) has been conducted. The research involved the period between 1965 and 2017. Woody plant undergrowth was considered in 30 plots, 5 × 5 m in size. The first generations were recorded from 1967–1969. The regeneration has become regular since 1978 and its intensity has been increasing since then. Climate warming is driving these processes. Correlation analysis revealed significant relationships between the number of Pinus sibirica seedlings and the minimum temperature in August and September of the current year, the minimum temperatures in May, June, and November of the previous year, the maximum temperatures in May and August of the current year, and precipitation in March of both the current and previous years. However, the young tree growth rate remains low to date (the height at an age of 45–50 years is approximately 114 ± 8.8 cm). At the same time, its open crowns are rare single lateral shoots. The length of the side shoots exceeds its height by 4–5 times, and the length of the lateral roots exceeds its height by 1.2–1.5 times. This is an indicator of the extreme conditions for this tree species. With the current rates of climate warming and the Pinus sibirica tree growth trends, the revealed relationships allow for the prediction that in 20–25 years, the mountain tundra in the studied Northern Urals plateau could develop underground-closed forest communities with a certain forest relationship. The research results are of theoretical importance for clarifying the forest-tundra ecotone concept. From a practical point of view, the revealed relationship can be used to predict the trend in forest ecosystem formation in the mountain forest-tundra ecotone.

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.

Simultaneous Ozone and High Light Treatments Reveal an Important Role for the Chloroplast in Co-ordination of Defense Signaling

Plants live in a world of changing environments, where they are continuously challenged by alternating biotic and abiotic stresses. To transfer information from the environment to appropriate protective responses, plants use many different signaling molecules and pathways. Reactive oxygen species (ROS) are critical signaling molecules in the regulation of plant stress responses, both inside and between cells. In natural environments, plants can experience multiple stresses simultaneously. Laboratory studies on stress interaction and crosstalk at regulation of gene expression, imply that plant responses to multiple stresses are distinctly different from single treatments. We analyzed the expression of selected marker genes and reassessed publicly available datasets to find signaling pathways regulated by ozone, which produces apoplastic ROS, and high light treatment, which produces chloroplastic ROS. Genes related to cell death regulation were differentially regulated by ozone versus high light. In a combined ozone + high light treatment, the light treatment enhanced ozone-induced cell death in leaves. The distinct responses from ozone versus high light treatments show that plants can activate stress signaling pathways in a highly precise manner.

Ozone Impact on Emission of Biogenic Volatile Organic Compounds in Three Tropical Tree Species From the Atlantic Forest Remnants in Southeast Brazil

Plants emit a broad number of Biogenic Volatile Organic Compounds (BVOCs) that can impact urban ozone (O₃) production. Conversely, the O₃ is a phytotoxic pollutant that causes unknown alterations in BVOC emissions from native plants. In this sense, here, we characterized the constitutive and O₃-induced BVOCs for two (2dO₃) and four (4dO₃) days of exposure (O₃ dose 80 ppb) and evaluated the O₃ response by histochemical techniques to detect programmed cell death (PCD) and hydrogen peroxide (H₂O₂) in three Brazilian native species. Croton floribundus Spreng, Astronium graveolens Jacq, and Piptadenia gonoacantha (Mart.) JF Macbr, from different groups of ecological succession (acquisitive and conservative), different carbon-saving defense strategies, and specific BVOC emissions. The three species emitted a very diverse BVOC composition: monoterpenes (MON), sesquiterpenes (SEQ), green leaf volatiles (GLV), and other compounds (OTC). C. floribundus is more acquisitive than A. graveolens. Their most representative BVOCs were methyl salicylate-MeSA (OTC), (Z) 3-hexenal, and (E)-2-hexenal (GLV), γ-elemene and (-)-β-bourbonene (SEQ) β-phellandrene and D-limonene (MON), while in A. graveolens were nonanal and decanal (OTC), and α-pinene (MON). Piptadenia gonoachanta is more conservative, and the BVOC blend was limited to MeSA (OTC), (E)-2-hexenal (GLV), and β-Phellandrene (MON). The O₃ affected BVOCs and histochemical traits of the three species in different ways. Croton floribundus was the most O₃ tolerant species and considered as an SEQ emitter. It efficiently reacted to O₃ stress after 2dO_3, verified by a high alteration of BVOC emission, the emergence of the compounds such as α-Ionone and trans-ß-Ionone, and the absence of H₂O₂ detection. On the contrary, A. graveolens, a MON-emitter, was affected by 2dO₃ and 4dO₃, showing increasing emissions of α-pinene and β-myrcene, (MON), γ-muurolene and β-cadinene (SEQ) and H₂O₂ accumulation. Piptadenia gonoachanta was the most sensitive and did not respond to BVOCs emission, but PCD and H₂O₂ were highly evidenced. Our results indicate that the BVOC blend emission, combined with histochemical observations, is a powerful tool to confirm the species' tolerance to O₃. Furthermore, our findings suggest that BVOC emission is a trade-off associated with different resource strategies of species indicated by the changes in the quality and quantity of BVOC emission for each species.

Does Technological Innovation Curb O3 Pollution? Evidence from Three Major Regions in China

At the end of 2020, when China’s three-year Blue Sky Protection Campaign was successfully concluded, the main pollutants, led by O₃, increased instead of decreasing, creating a new air pollution problem. In this paper, the impact of the technological innovation level on O₃ pollution and its inter-regional differences across three major regions from 2014 to 2019 are studied using the dynamic spatial Durbin model. Generally, in terms of ozone pollution showing significant spatial correlation, technological innovations in China are still not effective in curbing ozone pollution. Furthermore, technological innovation is a key factor affecting ozone pollution, and it is heterogeneous, demonstrating that the impact of technological innovation on O₃ pollution is different among regions. Technological innovation in Beijing–Tianjin–Hebei significantly reduces local O₃ pollution with spillover, while technological innovation in the Yangtze River Delta instead significantly exacerbates local O₃ pollution, and the impact of technological innovation on O₃ pollution in the Fenwei Plain is not significant. Third, other factors in O₃ pollution also differ between regions, with the number of cars and the amount of foreign capital actually utilized being the main factors. Therefore, we should pay attention to the spillover of O₃ pollution and technological innovation and strengthen regional cooperation according to our own characteristics to effectively suppress O₃ pollution. Finally, the findings of this paper are representative, which provides a possible reference for other similar national or regional studies.

Characteristics and Impact of VOCs on Ozone Formation Potential in a Petrochemical Industrial Area, Thailand

In this study, the ambient concentrations of volatile organic compounds (VOCs) were intensively measured from January 2012 to December 2016 using an evacuated canister and were analyzed using a gas chromatography/mass spectrophotometer (GC/MS) based on the US EPA TO-15 in the community and industrial areas of the largest petroleum refinery and petrochemical industrial complex in Map Ta Phut Thailand. The ternary diagram was used to identify the source of VOCs. Reactivity of VOCs on their ozone formation potential (OFP) were quantified by the maximum incremental reactivity coefficient method (MIR) and propylene-equivalent concentration methods. Results from the study revealed that aromatic hydrocarbon was the dominant group of VOCs greatly contributing to the total concentration of measured VOCs. Among the measured VOCs species, toluene had the highest concentration and contributed as the major precursor to ozone formation. The ternary analysis of benzene:toluene:ethybenzene ratios indicated that VOCs mainly originated from mobile sources and industrial processes. Within the industrial area, measured VOC concentration was dominated by halogenated hydrocarbons, and alkene was the highest contributor to ozone formation. The propylene-equivalent concentration method was also used to evaluate the reactivity of VOCs and their role in ozone formation, and secondly to support findings from the MIR method.

The Dynamical Role of the Chesapeake Bay on the Local Ozone Pollution Using Mesoscale Modeling—A Case Study

This study investigated the dynamic influence of the Chesapeake Bay (CB) on local ozone (O3) concentration and distribution using a weather forecasting model. The Weather Research and Forecasting model coupled with Chemistry (WRF–Chem) was employed to simulate O3 production and transportation near the CB. Baseline (water) as well as sensitivity (nowater) model experiments of bay circulation were carried out with and without bay water by changing the water surface from water to land (loam). First, the model performance simulating O3 was evaluated using the baseline experiment results and AirNow surface wind and O3 observations. The results showed that the model overestimates surface O3 by up to 20–30%. Further, the comparisons of the baseline and sensitivity experiments revealed higher O3 mixing ratios, primarily due to the resulting bay breeze circulation. These increases, after considering model overestimation, represent a mean bay dynamics circulation-induced contribution of up to 10% at night and 5% during the day. Furthermore, the boundary layer over northern CB, where it is at its narrowest width, was higher (by 1.2 km on average) during daytime due to higher surface temperatures observed. The boundary layer depth difference between the northern, central, and southern regions of the bay leads to a differential in the role of bay circulation dynamics in the observed O3 increase. The relatively wider swath of water surface over southern CB resulted in a lower boundary layer depth and stronger breeze circulation and this circulation contributed to O3 concentrations. Moreover, since the case selected has a minimal bay breeze circulation, the associated surface ozone enhancements represent what is expected at least at a minimum.

Ozone Monitoring in the Baikal Region (East Siberia): Spatiotemporal Variability under the Influence of Air Pollutants and Site Conditions

This article analyses the results of year-round automatic ozone monitoring in seven cities of the Baikal region (southeastern Siberia). We reveal that significant differences in the spatiotemporal variability of the average daily ozone concentrations depend on different anthropogenic loads. In large cities with heavy industry, which are located in the Angara River valley, the ozone concentrations were minimal and changed little during the year: less than 5 µg/m3 in the Angarsk city and 20–30 µg/m3 in the Irkutsk city. In the settlements of a less polluted region, the Selenga River valley, the ozone concentrations were significantly higher, and the annual ozone variability was typical of East Siberia: the maximum in spring (60 to 70 μg/m3) and the minimum in autumn and winter (10 to 30 μg/m3). The maximum ozone concentrations were observed in rural conditions (Listvyanka station), up to 80–100 μg/m3 during the spring maximum. Nitrogen oxides had the main influence on ozone depletion in the surface atmosphere of the cities, especially in winter, the season of maximum burning of fossil fuels (negative correlation can reach −0.9). In cities with heavy industry, the effect of NOx on ozone was weaker. Perhaps other anthropogenic impurities can also affect ozone suppression in these cities, which have not yet been studied.

Individual and Interactive Effects of Elevated Ozone and Temperature on Plant Responses

From the preindustrial era to the present day, the tropospheric ozone (O3) concentration has increased dramatically in much of the industrialized world due to anthropogenic activities. O3 is the most harmful air pollutant to plants. Global surface temperatures are expected to increase with rising O3 concentration. Plants are directly affected by temperature and O3. Elevated O3 can impair physiological processes, as well as cause the accumulation of reactive oxygen species (ROS), leading to decreased plant growth. Temperature is another important factor influencing plant development. Here, we summarize how O3 and temperature elevation can affect plant physiological and biochemical characteristics, and discuss results from studies investigating plant responses to these factors. In this review, we focused on the interactions between elevated O3 and temperature on plant responses, because neither factor acts independently. Temperature has great potential to significantly influence stomatal movement and O3 uptake. For this reason, the combined influence of both factors can yield significantly different results than those of a single factor. Plant responses to the combined effects of elevated temperature and O3 are still controversial. We attribute the substantial uncertainty of these combined effects primarily to differences in methodological approaches.

Leaf Fluxes of Carbon Dioxide, Methane and Biogenic Volatile Organic Compounds of the Urban Trees Platanus × acerifolia and Schinus molle in Santiago, Chile

This study assessed leaf fluxes of CO2, CH4 and biogenic volatile organic compounds (BVOC) for two common urban tree species, Platanus × acerifolia (exotic) and Schinus molle (native), widely distributed in Santiago, Chile. The emission factors (EF) and the Photochemical Ozone Creation Index (POCI) for S. molle and P. × acerifolia were estimated. The global EF was 6.4 times higher for P. × acerifolia compared with S. molle, with similar rates of photosynthesis for both species. Isoprene represented more than 86% of the total BVOCs leaf fluxes being 7.6 times greater for P. × acerifolia than S. molle. For P. × acerifolia, BVOCs represented 2% of total carbon fixation while representing 0.24% for S. molle. These results may suggest that plant species growing outside their ecological range may exhibit greater BVOCs leaf fluxes, proportional to photosynthesis, compared to well-adapted ones. The results found may contribute to better urban forest planning.

Urban conditions affect soil characteristics and physiological performance of three evergreen woody species

Physiological studies conducted mainly in metropolitan areas demonstrated that urban environments generate stressful conditions for plants. However, less attention has been paid to plant response to urban conditions in small cities. Here, we evaluated to what extent the health and physiological functions of some Mediterranean urban species [Quercus ilex L., Nerium oleander L. and Pittosporum tobira (Thunb.) W.T. Aiton] were impacted by urban and peri-urban conditions in Pisa (Italy), a small medieval city with narrow streets that impede efficient public transport causing oversized private transport. Experimental period spanned from late-summer to winter in concomitance with the sharp increase in air pollutants. Climate and air quality, soil physical and chemical properties, and plant physiological traits including leaf gas exchanges, chlorophyll fluorescence and leaf pigments were assessed. In soil, the organic carbon affected aggregates and water stability and the concentrations of some micro-elements decreased in winter. Air pollutants impaired leaf gas exchanges and photochemical processes at photosystem II, depending on species, season, and urban conditions. Shrubs were more susceptible than the tree species, highlighting that the latter adapted better to pollutants along an urban-peri-urban transect in Mediterranean environments. This study gives information on the physiological adaptability of some of the most frequent Mediterranean urban species to stressful conditions and demonstrated that, even in a small city, urban conditions influence the physiology and development of vegetation, affecting the plant health status and its ability to provide key ecosystem services.

Effects of Evaporative Emissions Control Measurements on Ozone Concentrations in Brazil

In this work, the possible benefits obtained due to the implementation of evaporative emissions control measures, originating from vehicle fueling processes, on ozone concentrations are verified. The measures studied are: (1) control at the moment when the tank trucks supply the fuel to the gas stations (Stage 1); (2) control at the moment when the vehicles are refueled at the gas stations, through a device installed in the pumps (Stage 2); (3) same as the previous control, but through a device installed in the vehicles (ORVR). The effects of these procedures were analyzed using numerical modeling with the VEIN and WRF/Chem models for a base case in 2018 and different emission scenarios, both in 2018 and 2031. The results obtained for 2018 show that the implementation of Stages 1 and 2 would reduce HCNM emissions by 47.96%, with a consequent reduction of 19.9% in the average concentrations of tropospheric ozone. For 2031, the greatest reductions in ozone concentrations were obtained with the scenario without ORVR, and with Stage 1 and Stage 2 (64.65% reduction in HCNM emissions and 31.93% in ozone), followed by the scenario with ORVR and with Stage 1 and Stage 2 (64.39% reduction in HCNM emissions and 32.98% in ozone concentrations).

The Influence of Ozone on Net Ecosystem Production of a Ryegrass–Clover Mixture under Field Conditions

In order to understand the effect of phytotoxic tropospheric ozone (O3) on terrestrial vegetation, we quantified the impact of current O3 concentration ([O3]) on net ecosystem production (NEP) when compared to the conditions of the pre-industrial era. We compared and tested linear mixed-effects models based on [O3] and stomatal O3 flux (Fsto). The managed ryegrass–clover (Lolium perenne and Trifolium pratense) mixture was grown on arable land in the Czech Republic, Central Europe. Values of [O3] and Fsto were measured and calculated based on resistance analogy, respectively, while NEP was calculated from eddy covariance CO2 fluxes. We found the Fsto-based model more precise when compared to measured NEP. High Fsto was found even at low [O3], while broad summer maximum of [O3] was not necessarily followed by significant NEP decline, due to low soil water content leading to a low stomatal conductivity and Fsto. Comparing to low pre-industrial O3 conditions, current levels of O3 resulted in the reduction of cumulative NEP over the entire growing season, up to 29.7 and 13.5% when the [O3]-based and Fsto-based model was applied, respectively. During the growing season, an O3-induced reduction of NEP ranged between 13.1% in May and 26.2% in July when compared to pre-industrial Fsto levels. Looking to the future, high [O3] and Fsto may lead to the reduction of current NEP by approximately 13.3% on average during the growing season, but may increase by up to 61–86.6% in autumn, indicating further O3-induced acceleration of the senescence. These findings indicate the importance of Fsto and its inclusion into the models estimating O3 effects on terrestrial vegetation. The interaction between environmental factors and stomatal conductance is therefore discussed in detail.

Air Quality Assessment in the Central Mediterranean Sea (Tyrrhenian Sea): Anthropic Impact and Miscellaneous Natural Sources, including Volcanic Contribution, on the Budget of Volatile Organic Compounds (VOCs)

The results of air pollution assessment during a 2017 cruise of the research ship “Minerva Uno” in the Tyrrhenian Sea are reported. Volatile Organic Compounds (VOCs), Oxygenated Volatile Organic Compounds (OVOCs), and pollutants such as nitrogen oxides, ozone, and sulphur dioxide were monitored throughout the cruise. The shallow waters at ten sites of the investigated area were also analyzed. Organic compounds such as n-alkanes showed a bimodal distribution with a maximum at C5–C6 and C10–C11 at sites the most affected by anthropic impact, whereas remote sites showed a unimodal distribution with maximum at C10–C11. The most abundant atmospheric OVOC was acetone (3.66 μg/m3), accounting for 38%; formaldehyde (1.23 μg/m3) and acetaldehyde (0.99 μg/m3) made up about 22–29% of the total. The influence of some natural sources as volcanoes, in the southern part of the Tyrrhenian Sea near the Aeolian arc was studied. This source did not induce any noticeable effect on the total amount of hydrocarbons nor on the levels of trace gases such as CFCs, whereas the trends of sulphur dioxide seemed to confirm a possible contribution. The impact of underwater emissions was observed near the Panarea and Vulcano islands, where lower pHs, high levels of Fe and Mn, and diagnostic of vent activity, were measured.

Exploring new strategies for ozone-risk assessment: A dynamic-threshold case study

Tropospheric ozone is a dangerous atmospheric pollutant for forest ecosystems when it penetrates stomata. Thresholds for ozone-risk assessment are based on accumulated stomatal ozone fluxes such as the Phytotoxic Ozone Dose (POD). In order to identify the effect of ozone on a Holm oak forest in central Italy, four flux-based ozone impact response functions were implemented and tested in a multi-layer canopy model AIRTREE and evaluated against Gross Primary Productivity (GPP) obtained from observations of Eddy Covariance fluxes of CO₂. To evaluate if a clear phytotoxic threshold exists and if it changes during the year, six different detoxifying thresholds ranging between 0 and 5 nmol O₃ m^-2 s^-1 were tested. The use of species-specific rather than more general response functions based on plant functional types (PFT) increased model accuracy (RMSE reduced by up to 8.5%). In the case of linear response functions, a threshold of 1 nmol m^-2 s^-2 produced the best results for simulations of the whole year, although the tolerance to ozone changed seasonally, with higher tolerance (5 nmol m^-2 s^-1 or no ozone impact) for Winter and Spring and lower thresholds in Summer and Fall (0-1 nmol m^-2 s^-1). A "dynamic threshold" obtained by extracting the best daily threshold values from a range of different simulations helped reduce model overestimation of GPP by 213 g C m^-2 y^-1 and reduce RMSE up to 7.7%. Finally, a nonlinear ozone correction based on manipulative experiments produced the best results when no detoxifying threshold was applied (0 nmol O₃ m^-2 s^-1), suggesting that nonlinear functions fully account for ozone detoxification. The evidence of seasonal changes in ozone tolerance points to the need for seasonal thresholds to predict ozone damage and highlights the importance of performing more species-specific manipulative experiments to derive response functions for a broad range of plant species.

Variation in Carbon Content among the Major Tree Species in Hemiboreal Forests in Latvia

This study was designed to estimate the variation in non-volatile carbon (C) content in different above- and belowground tree parts (stem, living branches, dead branches, stumps, coarse roots and small roots) and to develop country-specific weighted mean C content values for the major tree species in hemiboreal forests in Latvia: Norway spruce (Picea abies (L.) H. Karst.), Scots pine (Pinus sylvestris L.), birch spp. (Betula spp.) and European aspen (Populus tremula L.). In total, 372 sample trees from 124 forest stands were selected and destructively sampled. As the tree samples were pre-treated by oven-drying before elemental analysis, the results of this study represent the non-volatile C fraction. Our findings indicate a significant variation in C content among the tree parts and studied species with a range of 504.6 ± 3.4 g·kg−1 (European aspen, coarse roots) to 550.6 ± 2.4 g·kg−1 (Scots pine, dead branches). The weighted mean C content values for whole trees ranged from 509.0 ± 1.6 g·kg−1 for European aspen to 533.2 ± 1.6 g·kg−1 for Scots pine. Only in Norway spruce was the whole tree C content significantly influenced by tree age and size. Our analysis revealed that the use of the Intergovernmental Panel on Climate Change (IPCC) default C content values recommended for temperate and boreal ecological zones leads to a 5.1% underestimation of C stock in living tree biomass in Latvia’s forests. Thus, the country-specific weighted mean C content values for major tree species we provide may improve the accuracy of National Greenhouse Gas Inventory estimates.

Removal of VOCs by Ozone: n-Alkane Oxidation under Mild Conditions

Volatile organic compounds (VOCs) have a negative effect on both humans and the environment; therefore, it is crucial to minimize their emission. The conventional solution is the catalytic oxidation of VOCs by air; however, in some cases this method requires relatively high temperatures. Thus, the oxidation of short-chain alkanes, which demonstrate the lowest reactivity among VOCs, starts at 250–350 °C. This research deals with the ozone catalytic oxidation (OZCO) of alkanes at temperatures as low as 25–200 °C using an alumina-supported manganese oxide catalyst. Our data demonstrate that oxidation can be significantly accelerated in the presence of a small amount of O3. In particular, it was found that n-C4H10 can be readily oxidized by an air/O3 mixture over the Mn/Al2O3 catalyst at temperatures as low as 25 °C. According to the characterization data (SEM-EDX, XRD, H2-TPR, and XPS) the superior catalytic performance of the Mn/Al2O3 catalyst in OZCO stems from a high concentration of Mn2O3 species and oxygen vacancies.