Explosive growth characteristics of 5.6-560 nm particles and deposition in human respiratory during spring in Yangtze River Delta region, China

Studying the contribution of regional transport to ultrafine particles (UFPs) and the deposition effect of nanoscale particles in human respiratory system is conducive to exploring the impact of atmospheric particles on the environment and human health. Based on the data set of number concentration spectrum in the particle size range of 5.6-560 nm in the spring of Hefei, the Yangtze River Delta region obtained by a fast mobility particle sizer, the explosive growth characteristics, potential source identification and deposition flux analysis of UFPs were systematically studied. The results showed that the frequency of new particle formation (NPF) events during spring was 31.5 %. SO2 and O3 contribute to NPF events. Daytime, higher temperature, stronger solar radiation and lower humidity were more conducive to the explosive growth of UFPs. In addition, regional transport of pollutants from the cities around Hefei played an important role in the accumulation mode particles, which were mainly affected by the land-source air mass from northwest Jiangsu (23.64 %) and the sea-source air mass from the Yellow Sea (23.99 %). It was worth noting that approximately 10,406 ng of UFPs enters the human respiratory system every day. The main deposition area of 5.6-560 nm nanoscale particles was alveolar, 5.6-400 nm is more likely to be deposited on alveolar, while nanoscale particles with particle size between 400 and 560 nm is more likely to be deposited on head airways. This study identified the deposition risk of nanoscale particles in the respiratory system under different particle sizes.

Identification of Wheat Stripe Rust Inoculum Sources and Dispersal Routes Responsible for Initial Rust Establishment in Southern Henan of China

Wheat stripe rust (yellow rust), caused by Puccinia striiformis f. sp. tritici (Pst), is an important airborne disease worldwide. Pst inoculum strength in southern Henan in winter or early spring is important for spring epidemics in the main autumn-sown wheat-growing regions of China. However, there is limited knowledge about the source and time of initial infection on winter wheat in southern Henan. The first occurrence of wheat stripe rust in southern Henan was recorded annually from 2011 to 2022, from which we used the backward trajectory approach to infer the likely source of Pst inoculum responsible for the initial disease occurrence. The results suggested that the Pst inoculum responsible for initial rust established in the winter in southern Henan originated from the Gansu Pst oversummering area in China, whereas it originated from the adjacent winter Pst sporulation regions in southern Shaanxi and northwestern Hubei if Pst symptoms were first observed in early spring in southern Henan. Another possible Pst source is southern Hubei where Pst can also sporulate in the winter. Thus, early Pst development in winter in the main wheat production region in China (Henan) is likely to be caused by Pst inoculum spread from the oversummering inocula or Pst epidemics in autumn seedlings in Gansu.

Dual-isotope ratios of carbonaceous aerosols for seasonal observation and their assessment as source indicators

Carbonaceous aerosols exhibit seasonal variations due to a complex interplay of emission sources, meteorological conditions, and chemical processes. This study presents the first year-round dual‑carbon isotopic analysis of carbonaceous aerosols in Northeastern Europe (Lithuania). The emphasis was placed on the processes affecting carbonaceous submicron particle (PM1) concentrations and their isotopic composition (δ13CTC, fc) during different seasons. Aerosol particles were collected in the two distinct sites: at an urban background site (Vilnius) and a coastal site (Preila). The concentrations of total carbon (TC) and black carbon (BC) varied both spatially and temporally. The annual average concentrations were 4 μg/m3 for TC and 2.3 μg/m3 for BC at the urban background site. They were considerably lower at the coastal site with 2.9 μg/m3 for TC and 0.74 μg/m3 for BC. The peak concentrations of TC and BC that occur during the cold season indicate a significant impact from residential heating. The δ13C in aerosols exhibited a distinct seasonal cycle with depleted δ13CTC values during the warm season (April-October). Through the integration of isotopic composition, contemporary carbon (fc), and BC source apportionment, we achieved precise predictions of isotopic parameter changes, encompassing pollution sources and the influence of meteorological parameters. To better understand the respective contributions of local and regional sources, air mass trajectories, wind patterns (speed and direction), and the polar conditional probability function (CPF) were studied in parallel. The study indicates that the isotopic composition of PM1 at both sites is primarily controlled by emission sources (local and regional), while meteorological conditions (temperature and mixing layer height) have less influence. These variations have important implications for regional air quality, climate dynamics, and public health, which are persistently subject to continuous research and monitoring.

Long-Term Halocarbon Observations in an Urban Area of the YRD Region, China: Characteristic, Sources Apportionment and Health Risk Assessment

To observe the long-term variations in halocarbons in the Yangtze River Delta (YRD) region, this study analyzes halocarbon concentrations and composition characteristics in Shanxi from 2018 to 2020, exploring their origins and the health effects. The total concentration of halocarbons has shown an overall increasing trend, which is driven by both regulated substances (CFC-11 and CFC-113) and unregulated substances, such as dichloromethane, chloromethane and chloroform. The results of the study also reveal that dichloromethane (1.194 ± 1.003 to 1.424 ± 1.004 ppbv) and chloromethane (0.205 ± 0.185 to 0.666 ± 0.323 ppbv) are the predominant halocarbons in Shanxi, influenced by local and northwestern emissions. Next, this study identifies that neighboring cities in Zhejiang Province and other YRD areas are potentially affected by backward trajectory models. Notably, chloroform and 1,2-dichloroethane have consistently surpassed acceptable thresholds, indicating a significant carcinogenic risk associated with solvent usage. This research sheds light on the evolution of halocarbons in the YRD region, offering valuable data for the control and reduction in halocarbon emissions.

Atmospheric H2O2 during haze episodes in a Chinese megacity: Concentration, source, and implication on sulfate production

Atmospheric hydrogen peroxide (H2O2), as an important oxidant, plays a key role in atmospheric chemistry. To reveal its characteristics in polluted areas, comprehensive observations were conducted in Zhengzhou, China from February 22 to March 4, 2019, including heavy pollution days (HP) and light pollution days (LP). High NO concentrations (18 ± 26 ppbv) were recorded in HP, preventing the recombination reaction of two HO2• radicals. Surprisingly, higher concentrations of H2O2 were observed in HP (1.5 ± 0.6 ppbv) than those in LP (1.2 ± 0.6 ppbv). In addition to low wind speed and relative humidity, the elevated H2O2 in HP could be mainly attributed to intensified particle-phase photoreactions and biomass burning. In terms of sulfate formation, transition-metal ions (TMI)-catalyzed oxidation emerged as the predominant oxidant pathway in both HP and LP. Note that the average H2O2 oxidation rate increased from 3.6 × 10-2 in LP to 1.1 × 10-1 μg m-3 h-1 in HP. Moreover, the oxidation by H2O2 might exceed that of TMI catalysis under specific conditions, emerging as the primary driver of sulfate formation.

The effect of cross-regional transport on ozone and particulate matter pollution in China: A review of methodology and current knowledge

China is currently one of the countries impacted by severe atmospheric ozone (O3) and particulate matter (PM) pollution. Due to their moderately long lifetimes, O3 and PM can be transported over long distances, cross the boundaries of source regions and contribute to air pollution in other regions. The reported contributions of cross-regional transport (CRT) to O3 and fine PM (PM2.5) concentrations often exceed those of local emissions in the major regions of China, highlighting the important role of CRT in regional air pollution. Therefore, further improvement of air quality in China requires more joint efforts among regions to ensure a proper reduction in emissions while accounting for the influence of CRT. This review summarizes the methodologies employed to assess the influence of CRT on O3 and PM pollution as well as current knowledge of CRT influence in China. Quantifying CRT contributions in proportion to O3 and PM levels and studying detailed CRT processes of O3, PM and precursors can be both based on targeted observations and/or model simulations. Reported publications indicate that CRT contributes by 40-80 % to O3 and by 10-70 % to PM2.5 in various regions of China. These contributions exhibit notable spatiotemporal variations, with differences in meteorological conditions and/or emissions often serving as main drivers of such variations. Based on trajectory-based methods, transport pathways contributing to O3 and PM pollution in major regions of China have been revealed. Recent studies also highlighted the important role of horizontal transport in the middle/high atmospheric boundary layer or low free troposphere, of vertical exchange and mixing as well as of interactions between CRT, local meteorology and chemistry in the detailed CRT processes. Drawing on the current knowledge on the influence of CRT, this paper provides recommendations for future studies that aim at supporting ongoing air pollution mitigation strategies in China.

Evaluating the multi-variable influence on O3, NO2, and HCHO using BRTs and RF model

This study addresses significant knowledge gaps in understanding the complex interplay between atmospheric chemistry and synoptic conditions. Using emerging machine learning techniques-Boosted Regression Trees (BRTs) and Random Forest (RF) models-we investigate the influence of synoptic conditions on pollutant levels. Several BRTs and RF models are developed to estimate surface concentrations of ozone (O3), nitrogen dioxide (NO2), and formaldehyde (HCHO). By considering a range of algorithmic structures and explanatory variables for each pollutant, the research aims to identify the most skillful predictive approaches and influential factors governing pollutant levels. The design seeks to highlight key determinants of concentration patterns without constraining the investigation to pre-defined model structures or explanatory variable sets. Introducing a novel methodology, Correlation Coefficient Differential Evaluation (C2DE), we quantitatively assess the influence of explanatory variables. C2DE reveals significant contributions from spatial variables (i.e., trajectory clusters at varying altitudes), formaldehyde to nitrogen dioxide ratio (FNR), and meteorological parameters. Specifically, spatial variables contribute approximately 28 % to O3 concentrations, while the FNR accounts for around 5.2-9.8 % of the overall influence. For NO2 and HCHO, spatial variables contribute around 26.5 % and 32.1 %, respectively. Moreover, when considering the combined influence of meteorological parameters, these collectively explain about 45.34 %, 35.31 %, and 45.41 % of the variations in O3, NO2, and HCHO concentrations, respectively. Thus, C2DE provides valuable insights into the relative contributions of these factors, aiding in the comprehensive evaluation of air quality dynamics. This underscores the need for a multifaceted approach to comprehending and effectively addressing air pollution before devising its control strategies.

Temporal variability, meteorological influences, and long-range transport of atmospheric aerosols over two contrasting environments Agartala and Patiala in India

The present study focused on the temporal variability, meteorological influences, potential sources, and long-range transport of atmospheric aerosols over two contrasting environments during 2011-2013. We have chosen Agartala (AGR) city in Northeast India as one of our sites representing the rural-continental environment and Patiala (PTA) as an urban site in Northwest India. The seasonal averaged equivalent black carbon (eBC) concentration in AGR ranges from 1.55 to 38.11 µg/m3 with an average value of 9.87 ± 8.17 µg/m3, whereas, at an urban location, PTA value ranges from 1.30 to 15.57 µg/m3 with an average value of 7.83 ± 3.51 µg/m3. The annual average eBC concentration over AGR was observed to be ~ 3 times higher than PTA. Two diurnal peaks (morning and evening) in eBC have been observed at both sites but were observed to be more prominent at AGR than at PTA. Spectral aerosol optical depth (AOD) has been observed to be in the range from 0.33 ± 0.09 (post-monsoon) to 0.85 ± 0.22 (winter) at AGR and 0.47 ± 0.04 (pre-monsoon) to 0.74 ± 0.09 (post-monsoon) at PTA. The concentration of eBC and its diurnal and seasonal variation indicates the primary sources of eBC as local sources, synoptic meteorology, planetary boundary layer (PBL) dynamics, and distant transportation of aerosols. The wintertime higher values of eBC at AGR than at PTA are linked with the transportation of eBC from the Indo-Gangetic Plain (IGP). Furthermore, it is evident that eBC aerosols are transported from local and regional sources, which is supported by concentration-weighted trajectory (CWT) analysis results.

Spatiotemporal dynamics, traceability analysis, and exposure risks of antibiotic resistance genes in PM2.5 in Handan, China

Fine particulate matter (PM2.5) seriously affects environmental air quality and human health, and antibiotic resistance genes (ARGs) in PM2.5 posed a great challenge to clinical medicine. The year of 2013-2017 was an important 5-year period for the implementation of Air Pollution Prevention and Control Action Plan (APPCAP) in China. Here, we took Handan, a PM2.5 polluted city in northern China, as the research object and analyzed ARGs in PM2.5 in winter (January) from 2013 to 2017. The results showed that the abundance of ARGs was the highest in 2013 (3.7 × 10-2 copies/16S rRNA), and ARGs were positively correlated with air quality index (AQI) (r = 0.328, P < 0.05) and PM2.5 concentration (r = 0.377, P = 0.020 < 0.05) in the 5-year period. The ARGs carried by PM2.5 in four functional regions of sewage treatment plant, steel works, university, and park showed that sul1 and qepA had higher abundance in each functional region, and the total ARG abundance in sewage treatment plant (1.3 × 10-1 copies/16S rRNA) was the highest, while lowest in park (2.0 × 10-3 copies/16S rRNA). Potential source contribution function (PSCF) and concentration-weighted trajectory (CWT) model were used to trace the pollutants at the sampling points, which indicated that the surrounding cities contributed more than quarter to the sampling points. Therefore, regional transportation reduces the spatial distribution difference of ARGs in PM2.5. The exposure dose of ARGs in different functional regions illustrated that the total inhaled dose of ARGs in sewage treatment plant (1.7 × 105 copies/d) was the highest, while lowest in park (3.2 × 104 copies/d). This study is of great significance for assessing the distribution and sources of ARGs under the clean air initiative in China.

Recent changes in atmospheric input and primary productivity in the north Indian Ocean

Global oceanic regions are rapidly changing in terms of their temperature, oxygen, heat content, salinity and biogeochemistry. Since the biogeochemistry of the oceans is important and pivotal for global food production, and a major part of the world population relies on marine resources for their daily life and livelihood, it is imperative to monitor and find the spatio-temporal changes in the primary productivity of oceans. Here, we estimate the changes in Chlorophyll-a (Chl-a) and Net Primary Productivity (NPP) in the north Indian Ocean (NIO) basins of Bay of Bengal and Arabian Sea for the period 1998-2019. We find a substantial reduction of NPP in NIO since 1998 (-0.048 mg m^-3 day^-1 yr^-1) and the increase in sea surface temperature (SST) (+0.02 °C yr^-1) is the primary driver of this change. Furthermore, there is a significant (10-20%) change in the air mass or dust transport to NIO from the period Decade 1 (1998-2008) to Decade 2 (2009-2019). This change in air mass trajectories has also altered NPP in both basins through the changes in nutrient input and associated biogeochemistry. Henceforth, this study cautions the changes in primary productivity of NIO, and suggests regular assessments and continuous monitoring of the physical and biological processes from a perspective of food security and ecosystem dynamics.

A new strategy for risk assessment of PM2.5-bound elements by considering the influence of wind regimes

For regulatory purposes, air pollution has been reduced to management of air quality control regions (AQCR), by inventorying pollution sources and identifying the receptors significantly affected. However, beyond being source-dependent, particulate matter can be physically and chemically altered by factors and elements of climate during transport, as they act as local environmental constraints, indirectly modulating the adverse effects of particles on the environment and human health. This case study, at an industrial site in a Brazilian coastal city - Joinville, combines different methodologies to integrate atmospheric dynamics in a strategic risk assessment approach whereby the influence of different wind regimes on environmental and health risks of exposure to PM_2.5-bound elements, are analysed. Although Joinville AQCR has been prone to stagnation/recirculation events, distinctly different horizontal wind circulation patterns indicate two airsheds within the region. The two sampling sites mirrored these two conditions and as a result we report different PM_2.5 mass concentrations, chemical profiles, geo-accumulation, and ecological and human health risks. In addition, feedback mechanisms between the airsheds seem to aggravate the air quality and its effects even under good ventilation conditions. Recognizably, the risks associated with Co, Pb, Cu, Ni, Mn, and Zn loadings were extremely high for the environment as well as being the main contributors to elevated non-carcinogenic risks. Meanwhile, higher carcinogenic risks occurred during stagnation/recirculation conditions, with Cr as the major threat. These results highlight the importance of integrating local airshed characteristics into the risk assessment of PM_2.5-bound elements since they can aggravate air pollution leading to different risks at a granular scale. This new approach to risk assessment can be employed in any city's longer-term development plan since it provides public authorities with a strategic perspective on incorporating environmental constraints into urban growth planning and development zoning regulations.

Characteristics and source apportionment of some halocarbons in Hangzhou, eastern China during 2021

In recent years, eastern China has been identified as an important contributor to national and global emissions of halocarbons, some of which are ozone depletion substances (ODSs) that delay the recovery of the stratospheric ozone layer. However, the most recent characteristics and sources of halocarbons in eastern China remain unclear. Thus, hourly atmospheric observations of halocarbons were conducted in Hangzhou throughout 2021. The results showed that methylene chloride (CH₂Cl₂) was the most abundant halocarbon (2207 (25 %-75 % quantile: 1116-2848) ppt; parts per trillion) followed by chloromethane (CH₃Cl) (912 (683-1043) ppt), and 1,2-dichloroethane (CH₂ClCH₂Cl) (596 (292-763) ppt). Then, backward trajectory and potential source contribution function (PSCF) analysis show that the emission hot spots of halocarbons were concentrated in adjacent cities in Zhejiang and neighboring provinces in eastern China. Moreover, based on positive matrix factorization (PMF) analysis, industrial emission (38.7 %), solvent usage (32.6 %), and the refrigeration sector and biomass burning (23.7 %) were the main sources of halocarbons (observed in this study). This study reveals high concentrations and potential sources of halocarbons in eastern China, which are important for studying the recovery of the ozone layer.

Cruise observation of the marine atmosphere and ship emissions in South China Sea: Aerosol composition, sources, and the aging process

Marine atmospheric aerosols impact the global climate and biogeochemical cycles. However, how the composition, sources, and aging of these aerosols affect the above processes has not been thoroughly studied. Here, we conducted ship-based measurements in the northern South China Sea to investigate the chemical composition and aging of aerosols from various sources during the summer of 2019. Separate measurements were conducted at the bow (marine environment) and stern (cooking, smoking, and engine exhaust) of the ship. Source apportionment of organic aerosols (OAs) was conducted using positive matrix factorization (PMF) and trajectory models. The results showed that ship exhaust and coastal submicron particles were composed of comparable sulfate and organic fractions (both approximately 43%), distinct from the sulfate-dominated particles in the marine atmosphere (52-77%). PMF using the multilinear engine-2 solver identified five factors for the stern sampling period: hydrocarbon-like OA (HOA-I, 9%), slightly oxidized HOA (HOA-II, 25%), cooking OA (COA, 13%), cigarette smoke OA (CSOA, 4%), and low-volatility oxygenated OA (LV-OOA, 49%). The primary OAs (HOA-I/II + COA + CSOA), derived mostly from direct ship-related emissions, contributed to approximately half of the OAs, whereas the contribution from the highly aged marine atmosphere was only 20%. Notably, certain living-related emissions (i.e., COA and CSOA), which were often neglected in previous studies, might represent a considerable contribution to OA emissions from the ship. Four factors were identified for the bow sampling periods: HOA (13%), biomass burning OA (BBOA, 9%), semi-volatile OOA (7%), and LV-OOA (71%). The BBOAs from the Indo-China and Malay peninsulas were aged, converted to secondary organic aerosols (SOAs) during transport, and influenced by the combined photo-oxidation and liquid-phase reactions, indicating a substantial impact of BB on SOA formation. Our study highlights the influence of ship and inland emissions and their aging during transport on marine atmospheric aerosols.

Ozone pollution in London and Edinburgh: spatiotemporal characteristics, trends, transport and the impact of COVID-19 control measures

Air pollution remains the most serious environmental health issue in the United Kingdom while also carrying non-trivial economic costs. The COVID-19 lockdown periods reduced anthropogenic emissions and offered unique conditions for air pollution research. This study sources fine-granularity geo-spatial air quality and meteorological data for the capital cities of two UK countries (i.e. England's capital London and Scotland's capital Edinburgh) from the UK Automatic Urban and Rural Network (AURN) spanning 2016–2022 to assess long-term trends in several criteria pollutants (PM10, PM2.5, SO2, NO2, O3, and CO) and the changes in ozone pollution during the pandemic period. Unlike other studies conducted thus far, this research integrates several tools in trend estimation, including the Mann-Kendall test, the Theil-Sen estimator with bootstrap resampling, and the generalized additive model (GAM). Moreover, several investigations, including cluster trajectory analysis, pollution rose plots, and potential source contribution function (PSCF), are also employed to identify potential origin sources for air masses carrying precursors and estimate their contributions to ozone concentrations at receptor sites and downwind areas. The main findings reveal that most of the criteria pollutants show a decreasing trend in both geographies over the seven-year period, except for O3, which presents a significant ascending trend in London and a milder ascending trend in Edinburgh. However, O3 concentrations have significantly decreased during the year 2020 in both urban areas, despite registering sharp increases during the first lockdown period. In turn, these findings indicate on one hand that the O3 generation process is in the VOC-limited regime in both UK urban areas and, on the other hand, confirm previous findings that, when stretching the analysis period, diminishing ozone levels can lead to NOx reduction even in VOC-controlled geographies. Trajectory analysis reveals that northern Europe, particularly Norway and Sweden, is a principal ozone pollution source for Edinburgh, whereas, for London, mainland Europe (i.e., the Benelux countries) is another significant source. The results have important policy implications, revealing that effective and efficient NOx abatement measures spur ozone pollution in the short-term, but the increase can be transient. Moreover, policymakers in London and Edinburgh should consider that both local and transboundary sources contribute to local ozone pollution.

Meteorology governs the variation of Delhi's high particulate-bound chloride levels

A significant number of past studies have reported Delhi to witness some of the highest levels of particulate-bound chloride compared to anywhere else in the world. The present study employs long-term, highly time-resolved chloride measurements at the IIT Delhi campus from February 2020 to April 2021. The present work sheds light on the dependence of high chloride levels in Delhi on the winds from the northwest direction. The study makes use of linear regression models and stepped linear models to quantify the role of meteorological variables in driving the seasonal variation of chloride in Delhi. The results indicate that ∼85-88% of the variation in chloride concentration observed in Delhi can be attributed to meteorological parameters, mainly temperature (T), relative humidity (RH), and percentage of wind incoming from the northwest (%NW). The results also suggest that the primary chloride emissions remain relatively consistent year-round, and are regionally transported from Delhi's northwest. The results of this study provide valuable insights in understanding the nature of the sources and the variability associated with the chloride levels in Delhi and thus provide a basis for future emission control strategies.

Wet deposition of total dissolved nitrogen in Indo-Gangetic Plain (India)

Very limited information on the magnitude and environmental impacts of both inorganic and organic forms of nitrogen (N) wet deposition is available in India. Molar concentrations of inorganic (NH₄⁺ and NO₃^-) and organic N in rainwater were monitored at three different land use sites in Indo-Gangetic Plain (IGP) during the monsoon period (June-September) of 2017. It has been observed that dissolved organic N (DON) contributed significantly to the total dissolved N (TDN) ranging from 5 to 60%. Dissolved inorganic N (DIN = NH₄⁺ + NO₃^-) concentration was recorded as high as 221.0 μmol L^-1 at urban site to as low as 65.9 μmol L^-1 at the rural site. A similar pattern was also observed for DON. NH₄⁺ contribution to TDN had the order urban megacity (65%) > urban (70%) > rural (75%). Agriculture and animal husbandry are the primary sources of NH₄⁺ emissions in the rural site. However, NO₃^- has shown a contrasting trend at these sites (25%, 15%, and 8%, respectively). Wet deposition fluxes of atmospheric TDN were observed to be higher at urban sites. This can be attributed to a variety of local sources such as vehicular emission, microbial emissions, biomass burning, human excreta due to higher population density, and transportation from surrounding areas, as observed from concentration weighted trajectories (CWT) model and cluster analysis. Upwind region of IGP has experienced major influence of air mass transported from agriculturally rich northwest part of India. However, both the downwind sites have experienced by-and-large the influence of south-westerly air masses originated over the Arabian Sea. This study has found that the DON contributes significantly to TDN, and therefore, its inclusion for nitrogen budget assessment in South Asia is emphasized.

Transport routes and potential source areas of PM10 in Kirklareli, Turkey

In this study, the seasonal variation, transport routes, and potential source areas of PM₁₀ in the central district of Kirklareli (Turkey) were investigated. It was determined that PM₁₀ concentrations had the highest seasonal average value in autumn and the lowest seasonal average value in spring. Cumulative distributions of PM₁₀ concentrations data set were examined. In order to determine the air mass source and transport routes, the backward trajectories of the air masses obtained by using the hybrid single-particle Lagrangian integrated trajectory (HYSPLIT) model were run and cluster analysis, which is one of the multivariate statistical analyses, was performed. Cluster analysis results revealed that there are five main clusters affecting the receptor site in all four seasons. By defining the PM₁₀ concentrations data as an input to the potential source contribution function (PSCF) model, the probable locations of potential source areas were identified. It has been observed that there are obvious seasonal differences in the potential source areas of PM₁₀. High PSCF values were observed especially in Greece and the Mediterranean during the winter and especially in Albania and Greece during the spring. While high PSCF values were observed especially in the Anatolian side of Istanbul, Kocaeli, Sakarya, and the Black Sea coasts of these regions during the summer, they were observed especially in İzmir and Balikesir during the autumn.

Exposure to long-range transported particulate matter and modeling age-related particle deposition

Exposure to particulate matter (PM) is known to cause cardiovascular disease and increase mortality and morbidity. Asian dust (AD) is a meteorological phenomenon which affects much of East Asia year-round but especially during the spring months. Here, we have characterized concentrations of PM₁₀ and classified synoptic air flow trajectories using HYSPLIT model for Asian dust events (from March to April) in Jeju island, Korea. The ADE is a phenomenon in which sand and dust in the deserts of China or Mongolia rise mainly in spring and are blown away by western winds and gradually subside. The calculated inhaled PM₁₀ doses from specific microenvironments (home, work or school, and transportation) were from 5.28 to 101.48 μg depending on age group and different microenvironments while the calculated PM₁₀ inhaled doses for ADE ranged within 67.92 -769.27 μg. Also, we have evaluated the contribution of specific microenvironments to the exposure for different age groups using time-activity patterns and calculated inhaled PM₁₀ doses and deposited mass/mass flux so as to estimate exposure using multiple-path particle dosimetry (MPPD) model. The monthly average outdoor PM₁₀ concentration range was 29.3-65.4 μg/m³, whereas the monthly PM₁₀ concentration for ADE was 127.0-342.0 μg/m³. Air masses from clusters 1 and 2 were 24% and 29% (in 2017), clusters 2 and 3 were 24% and 32% (in 2018), and clusters 1 and 3 were 28% and 26% (in 2019) for ADE. In the aerosol deposition based on MPPD model, the corresponding values for daily particle deposited mass for two age groups ranged from 8.64 ×10^-5 μg (age 8) to 8.64 ×10^-4 μg (age 21). We assessed the PM_2.5 exposure considering time-activity patterns, age groups, and ADE exposure evaluation caused by long-range transport airflow; this could be helpful for assessing PM₁₀ exposure-related health evaluation.

Persistent pollution episodes, transport pathways, and potential sources of air pollution during the heating season of 2016-2017 in Lanzhou, China

As one of the most important industrial cities in Northwest China, Lanzhou currently suffers from serious air pollution. This study analyzed the formation mechanism and potential source areas of persistent air pollution in Lanzhou during the heating period from November 1, 2016 to March 31, 2017 based on the air pollutant concentrations and relevant meteorological data. Our findings indicate that particulate pollution was extremely severe during the study period. The daily PM_2.5 and PM₁₀ concentrations had significantly negative correlations with daily temperature, wind speed, maximum daily boundary layer height, while the daily PM_2.5 and PM₁₀ concentrations showed significantly positive correlations with daily relative humidity. Five persistent pollution episodes were identified and classified as either stagnant accumulation or explosive growth types according to the mechanism of pollution formation and evolution. The PM_2.5 and PM₁₀ concentrations and PM_2.5/PM₁₀ ratio followed a growing "saw-tooth cycle" pattern during the stagnant accumulation type event. Dust storms caused abrupt peaks in PM₁₀ and a sharp decrease in the PM_2.5/PM₁₀ ratio in explosive growth type events. The potential sources of PM₁₀ were mainly distributed in the Kumtag Desert in Xinjiang Uygur Autonomous Region, the Qaidam Basin and Hehuang Valley in Qinghai Province, and the western and eastern Hexi Corridor in Gansu Province. The contributions to PM₁₀ were more than 120 μg/m³. The important potential sources of PM_2.5 were located in Hehuang Valley in Qinghai and Linxia Hui Autonomous Prefecture in Gansu; the concentrations of PM_2.5 were more than 60 μg/m³.

Spatial Characteristics and Regional Transmission Analysis of PM2.5 Pollution in Northeast China, 2016-2020

Northeast China is an essential industrial development base in China and the regional air quality is severely affected by PM_2.5 pollution. In this paper, spatial autocorrelation, trajectory clustering, hotspot analysis, PSCF and CWT analysis are used to explore the spatial pollution characteristics of PM_2.5 and determine the atmospheric regional transmission pattern for 40 cities in Northeast China from 2016 to 2020. Analysis of PM_2.5 concentration characteristics in the northeast indicates that the annual average value and total exceedance days of PM_2.5 concentration in Northeast China showed a U-shaped change, with the lowest annual average PM_2.5 concentration (31 μg/m³) in 2018, decreasing by 12.1% year-on-year, and the hourly PM_2.5 concentration exploding during the epidemic lockdown period in 2020. A stable PM_2.5 pollution band emerges spatially from the southwest to Northeast China. Spatially, the PM_2.5 in Northeast China has a high degree of autocorrelation and a south-hot-north-cool characteristic, with all hotspots concentrated in the most polluted Liaoning province, which exhibits the H-H cluster pattern and hotspot per year. Analysis of the air mass trajectories, potential source contributions and concentration weight trajectories in Northeast China indicates that more than 74% of the air mass trajectories were transmitted to each other between the three heavily polluted cities, with the highest mean value of PM_2.5 pollution trajectories reaching 222.4 μg/m³, and the contribution of daily average PM_2.5 concentrations exceeding 60 μg/m³ within Northeast China. Pollution of PM_2.5 throughout the Northeast is mainly influenced by short-range intra-regional transport_, with long-range transport between regions also being an essential factor; organized integration is the only fundamental solution to air pollution.

Abundance of Ganoderma sp. in Europe and SW Asia: modelling the pathogen infection levels in local trees using the proxy of airborne fungal spore concentrations

Ganoderma comprises a common bracket fungal genus that causes basal stem rot in deciduous and coniferous trees and palms, thus having a large economic impact on forestry production. We estimated pathogen abundance using long-term, daily spore concentration data collected in five biogeographic regions in Europe and SW Asia. We hypothesized that pathogen abundance in the air depends on the density of potential hosts (trees) in the surrounding area, and that its spores originate locally. We tested this hypothesis by (1) calculating tree cover density, (2) assessing the impact of local meteorological variables on spore concentration, (3) computing back trajectories, (4) developing random forest models predicting daily spore concentration. The area covered by trees was calculated based on Tree Density Datasets within a 30 km radius from sampling sites. Variations in daily and seasonal spore concentrations were cross-examined between sites using a selection of statistical tools including HYSPLIT and random forest models. Our results showed that spore concentrations were higher in Northern and Central Europe than in South Europe and SW Asia. High and unusually high spore concentrations (> 90th and > 98th percentile, respectively) were partially associated with long distance transported spores: at least 33% of Ganoderma spores recorded in Madeira during days with high concentrations originated from the Iberian Peninsula located >900 km away. Random forest models developed on local meteorological data performed better in sites where the contribution of long distance transported spores was lower. We found that high concentrations were recorded in sites with low host density (Leicester, Worcester), and low concentrations in Kastamonu with high host density. This suggests that south European and SW Asian forests may be less severely affected by Ganoderma. This study highlights the effectiveness of monitoring airborne Ganoderma spore concentrations as a tool for assessing local Ganoderma pathogen infection levels.

Chemical and isotopic characteristics of PM2.5 over New Delhi from September 2014 to May 2015: Evidences for synergy between air-pollution and meteorological changes

The capital city of India, New Delhi, is experiencing serious PM_2.5 pollution in the form of recurrent hazy skies and smoky fog (SMOG) episodes in recent years. Besides source-emission strengths, frequency and time-spans of these air-pollution episodes are uncertain due to variable urban meteorological influences, preventing the formation of a cohesive policy to tackle air-quality degradation. About 70% mass of PM_2.5 particle is composed of Carbon (C), Nitrogen (N), and Sulphur (S) and, hence, their mass concentrations along with their stable isotopic imprints (viz. δ¹³C_PM2.5, δ¹⁵N_PM2.5 and δ³⁴S_PM2.5) provide powerful tools to gain insights into complex aerosol chemistry. This study presents the aforementioned data generated for PM_2.5 collected from New Delhi covering full post-monsoon, winter, and summer months of 2014-15. Temporal variability in the generated dataset was analyzed with variabilities in atmospheric concentrations of key gaseous species (NH₃, NO_x, and SO₂) and meteorological indices. The highest PM_2.5 concentrations were observed in winter months with enhanced aerosol N and S concentrations. Active biomass (crop-residue) burning in the northwest Indo-Gangetic Plains (IGP) appears to be the major source of aerosol TC for post-monsoon and winter months in addition to emission sources from the combustion of bio- and fossil- fuels. Aerosol TN contents appear to be largely impacted by ambient ammonia emissions, especially during winter. Aerosol TS contents could be manifested by emissions from coal combustion, road dust, and biogenic sulphur. Total C + N + S contents of PM_2.5 showed significant negative correlations with surface solar radiation and air-visibility. Both δ¹⁵N_PM2.5 and δ³⁴S_PM2.5 values show remarkable correlations with air-quality and meteorological parameters during winter months demonstrating considerable secondary cycling. Cluster analysis and concentrated weighted wind trajectories over New Delhi for the study-period showed ~64% and ~58% of air mass trajectories from the northwest (Punjab-Haryana) region during post-monsoon and winter months respectively.

Air pollutant emission characteristics and HYSPLIT model analysis during heating period in Shenyang, China

To find out the characteristics and sources of atmospheric pollutants during heating period in Shenyang, the study investigated the temporal and spatial distribution of pollutants, using data of six typical atmospheric pollutants (SO₂, NO₂, PM₁₀, PM_2.5, O₃, and CO) from November 2017 to March 2018 in 11 monitoring stations in Shenyang. These features were combined with the HYSPLIT model for backward trajectory simulation of heavily polluted weather. PM₁₀ and PM_2.5 are the main pollutants during heating period in Shenyang, with average concentrations of 90.26 μg/m³ and 56.92 μg/m³, respectively. The concentrations of various types of contaminants at the Taiyuan Street station were relatively high. PM₁₀ and PM_2.5 were relatively high in the southwestern area of Shenyang, gradually decreasing to the northeast. Only one heavy pollution event occurred during heating period in 2018. The results of the backward trajectory analysis of this heavy pollution event using HYSPLIT show that air masses from inland areas such as the southwest and northwest brought some particulate matter and atmospheric pollutants, which exacerbated Shenyang Air pollution in the city.

Identification of Long-Range Transport Pathways and Potential Source Regions of PM2.5 and PM10 at Akedala Station, Central Asia

Cluster analyses, potential source contribution function (PSCF) and concentration-weight trajectory (CWT) were used to identify the main transport pathways and potential source regions with hourly PM2.5 and PM10 concentrations in different seasons from January 2017 to December 2019 at Akedala Station, located in northwest China (Central Asia). The annual mean concentrations of PM2.5 and PM10 were 11.63 ± 9.31 and 19.99 ± 14.39 µg/m3, respectively. The air pollution was most polluted in winter, and the dominant part of PM10 (between 54 to 76%) constituted PM2.5 aerosols in Akedala. Particulate pollution in Akedala can be traced back to eastern Kazakhstan, northern Xinjiang, and western Mongolia. The cluster analyses showed that the Akedala atmosphere was mainly affected by air masses transported from the northwest. The PM2.5 and PM10 mainly came with air masses from the central and eastern regions of Kazakhstan, which are characterized by highly industrialized and semi-arid desert areas. In addition, the analyses of the pressure profile of back-trajectories showed that air mass distribution were mainly distributed above 840 hPa. This indicates that PM2.5 and PM10 concentrations were strongly affected by high altitude air masses. According to the results of the PSCF and CWT methods, the main potential source areas of PM2.5 were very similar to those of PM10. In winter and autumn, the main potential source areas with high weighted PSCF values were located in the eastern regions of Kazakhstan, northern Xinjiang, and western Mongolia. These areas contributed the highest PM2.5 concentrations from 25 to 40 µg/m3 and PM10 concentrations from 30 to 60 µg/m3 in these seasons. In spring and summer, the potential source areas with the high weighted PSCF values were distributed in eastern Kazakhstan, northern Xinjiang, the border between northeast Kazakhstan, and southern Russia. These areas contributed the highest PM2.5 concentrations from 10 to 20 µg/m3 and PM10 concentrations from 20 to 60 µg/m3 in these seasons.

Long-term (2003-2018) trends in aerosol chemical components at a high-altitude background station in the western North Pacific: Impact of long-range transport from continental Asia

This study examined the long-term trends in chemical components in PM_2.5 (particulate matter with aerodynamic diameter ≤2.5 μm) samples collected at Lulin Atmospheric Background Station (LABS) located on the summit of Mt. Lulin (2862 m above mean sea level) in Taiwan in the western North Pacific during 2003-2018. High ambient concentrations of PM_2.5 and its chemical components were observed during March and April every year. This enhancement was primarily associated with the long-range transport of biomass burning (BB) smoke emissions from Indochina, as revealed from cluster analysis of backward air mass trajectories. The decreasing trends in ambient concentrations of organic carbon (-0.67% yr^-1; p = 0.01), elemental carbon (-0.48% yr^-1; p = 0.18), and non-sea-salt (nss) K⁺ (-0.71% yr^-1; p = 0.04) during 2003-2018 indicated a declining effect of transported BB aerosol over the western North Pacific. These findings were supported by the decreasing trend in levoglucosan (-0.26% yr^-1; p = 0.20) during the period affected by the long-range transport of BB aerosol. However, NO₃^- displayed an increasing trend (0.71% yr^-1; p = 0.003) with considerable enhancement resulting from the air masses transported from the Asian continent. Given that the decreasing trends were for the majority of the chemical components, the columnar aerosol optical depth (AOD) also demonstrated a decreasing trend (-1.04% yr^-1; p = 0.0001) during 2006-2018. Overall decreasing trends in ambient (carbonaceous aerosol and nss-K⁺) as well as columnar (e.g., AOD) aerosol loadings at the LABS may influence the regional climate, which warrants further investigations. This study provides an improved understanding of the long-term trends in PM_2.5 chemical components over the western North Pacific, and the results would be highly useful in model simulations for evaluating the effects of BB transport on an area.

Transport Pathways and Potential Source Region Contributions of PM2.5 in Weifang: Seasonal Variations

As air pollution becomes progressively more serious, accurate identification of urban air pollution characteristics and associated pollutant transport mechanisms helps to effectively control and alleviate air pollution. This paper investigates the pollution characteristics, transport pathways, and potential sources of PM2.5 in Weifang based on PM2.5 monitoring data from 2015 to 2016 using three methods: Hybrid Single-Particle Lagrangian Integrated Trajectory (HYSPLIT), the potential source contribution function (PSCF), and concentration weighted trajectory (CWT). The results show the following: (1) Air pollution in Weifang was severe from 2015 to 2016, and the annual average PM2.5 concentration was more than twice the national air quality second-level standard (35 μg/m3). (2) Seasonal transport pathways of PM2.5 vary significantly: in winter, spring and autumn, airflow from the northwest and north directions accounts for a large proportion; in contrast, in summer, warm-humid airflows from the ocean in the southeastern direction dominate with scattered characteristics. (3) The PSCF and CWT results share generally similar characteristics in the seasonal distributions of source areas, which demonstrate the credibility and accuracy of the analysis results. (4) More attention should be paid to short-distance transport from the surrounding areas of Weifang, and a joint pollution prevention and control mechanism is critical for controlling regional pollution.

Detecting distant sources of airborne pollen for Poland: Integrating back-trajectory and dispersion modelling with a satellite-based phenology

Airborne pollen might be transported over thousands of kilometres, which has important ecological, evolutionary and clinical consequences. The long-distance transport (LDT) of birch (Betula sp.) pollen has been described in detail for northern Europe. However, a comprehensive analysis of this transport from other European regions is lacking. This study focused on the post-seasonal LDT of birch pollen to Poland (central Europe), with special attention paid to determining potential source areas of pollen and describing the causal mechanism favouring LDT episodes. Pollen monitoring (1997-2016) was conducted in Poznań and Rzeszów (500 km away from each other) using volumetric traps. The LDT episodes were characterized by analysing the (1) bi-hourly backward air mass trajectories using the Hybrid Single Particle Lagrangian Integrated Trajectory model (HYSPLIT); (2) sea level pressure (SLP) and 500 hPa geopotential height (z500) anomalies; and (3) patterns of the Enhanced Vegetation Index to determine the birch flowering time along the moving air mass trajectories. The potential locations of birch populations within broadleaved forests were estimated with GLOBCOVER data. Finally, the movement of pollen emitted from potential source areas was simulated using the HYSPLIT dispersion model. LDT episodes were mainly recorded in the first fortnight of May. The main source areas of pollen to Poland were western Russia, Belarus and to a lesser extent the eastern Baltic republics and the Scandinavian Peninsula. In most cases, a high-pressure centre located over Scandinavia and an elevated z500 over Germany-Denmark-Sweden favoured pollen transport. On average, the post-seasonal LDT episodes of birch pollen to Poland occur almost every year (Poznań) or every second year (Rzeszów). The episodes are highly variable in time; thus, the pollen concentration may unexpectedly cause allergy symptoms in sensitized patients. In some cases, these episodes may be extremely severe, thereby prolonging and strengthening the exposure to birch pollen allergens.

Characteristics and formation mechanism of persistent extreme haze pollution events in Chengdu, southwestern China

Extreme PM_2.5 and nonmethane hydrocarbon (NMHC) pollution often occurs simultaneously during the winter. To study the formation mechanism of two pollution events in Chengdu from 23 December 2016 to 31 January 2017, we explored the weather conditions, chemical composition, secondary pollutant conversion, aerosol hygroscopic growth, and potential source contribution function (PSCF) during this period. During the study period, the humidity was high (67.9%), the wind speed was low (1.0 m s^-1), the height of the planetary boundary layer was low (463.4 m), and the atmosphere remained stationary. The potential source regions of PM_2.5 and NMHCs were locally polluted sites in the southwestern and southern regions of Chengdu, affected by the southwesterly air mass trajectories. PM_2.5 and sulfur oxidation ratios (SOR), nitrogen oxidation ratios (NOR) and secondary organic aerosol formation potential (SOAP) showed a strong positive correlation. As pollution increased, the conversion from SO₂, NO_x and NMHCs to sulfate, nitrate and SOAs increased, resulting in an increase in the secondary aerosol concentration. As the relative humidity increases, aerosols begin to undergo rapid hygroscopic growth, which seriously affects the visibility of the atmosphere. In general, pollutant emissions, static weather, and secondary conversion, among other factors, lead to the occurrence of this persistent extreme haze pollution.

Transport Pathways and Potential Source Regions of PM2.5 on the West Coast of Bohai Bay during 2009–2018

Mass concentration data for particulate matter with an aerodynamic diameter less than or equal to 2.50 μm (PM2.5) combined with backward trajectory cluster analysis, potential source contribution function (PSCF), and concentration weighted trajectory (CWT) methods were used to investigate the transport pathways and potential source regions of PM2.5 on the west coast of Bohai Bay from 2009 to 2018. Two pathways responsible for the transportation of high PM2.5 levels were identified, namely a southerly pathway and a northwesterly pathway. The southerly pathway represented the major transport pathway of PM2.5 for all seasons. As a regional transport pathway, it had the greatest impact in winter, followed by autumn. The southerly transport pathway passed over the Shandong and Hebei provinces before reaching Tianjin: Air masses were transported within the boundary layer (below 925 hPa), representing a slow-moving air flow. The northwesterly pathway mostly occurred in winter and autumn and passed over desert and semidesert regions in Outer Mongolia, the sand lands of Inner Mongolia, and Hebei. The air masses associated with the northwesterly pathway represented fast-moving airflows responsible for long-range transportation of PM2.5. Two potential source regions that contributed to high PM2.5 loadings on the west coast of Bohai Bay were identified, “southerly source regions” and “northwesterly source regions”. The southerly source regions, with weighted CWT (WCWT) values in winter greater than 140.00 μg/m3, were anthropogenic source regions, including southern Hebei, western Shandong, eastern Henan, northern Anhui, and northern Jiangsu. The northwesterly source regions, with WCWT values in winter of 80.00–140.00 μg/m3, were natural source regions, encompassing central Inner Mongolia and southern Mongolia. In addition, the southerly transport pathway passed though anthropogenic source regions, while the northwesterly transport pathway passed though natural source regions. The impacts of anthropogenic source regions on PM2.5 loadings on the west coast of Bohai Bay were greater than those of natural source regions.

Characterization and Source Identification of Polybrominated Diphenyl Ethers (PBDEs) in Air in Xi'an: Based on a Five-Year Study

In order to assess polybrominated diphenyl ether (PBDE) atmospheric pollution levels in Xi’an, air samples were collected using a large flow air sampler from July 2008 to April 2013. In total, 134 samples were collected and 12 PBDE congeners were detected. Total PBDE concentrations (both gaseous and particulate phase) were 36.38–1054 pg/m³, with an average of 253.2 ± 198.4 pg/m³. BDE-209 was identified as the main PBDE component, with a corresponding concentration of 0.00–1041 pg/m³, accounting for 89.4% of total PBDEs. Principal component analysis results showed that PBDEs in Xi’an’s atmosphere mainly originated from commercial products containing penta-BDE, octa-BDE, and deca-BDE. The relative natural logarithm for partial pressure (RP) of PBDEs (gaseous phase) was calculated using the Clausius–Clapeyron equation. The gas flow trajectories at high, middle, and low RP values were analyzed by applying the backward trajectory model. These data indicated that the difference between trajectory distribution and concentration load on trajectories was huge under different RP values. PBDE concentrations (gaseous phase) weighted trajectory showed that the central and southwestern parts of Henan Province and the northwestern area of Hubei Province exhibited the darkest colors, and the daily average concentration contribution of PBDEs to the receiving point was >9 pg/m³, which indicates that these areas might be the main potential source areas of PBDEs in Xi’an’s atmosphere.

Pollution characteristics in a dusty season based on highly time-resolved online measurements in northwest China

To investigate the pollution characteristics and potential sources in a dusty season, an online analyzer was used to measure trace gases and major water-soluble ions in PM₁₀ from April 1st to May 29th, 2011 in Lanzhou. The average concentrations of HONO, HNO₃, HCl, SO₂ and NH₃ were 0.93, 1.16, 0.48, 9.29 and 5.54 μg/m³, respectively, and 2.8, 2.76, 8.28 and 2.48 μg/m³ for Cl^-, NO₃^-, SO₄^2- and NH₄⁺. In the non-dust period, diurnal variations of SO₄^2-, NO₃^- and their gaseous precursors showed similar change trend. NH₄⁺ showed unimodal pattern whereas NH₃ illustrated a bimodal pattern. HCl and Cl^- showed an opposite diurnal pattern. In the dust event, temporal profiles of HCl and Cl^-, SO₂ and SO₄^2- all presented similar change trend, and SO₄^2- and Cl^- preceded dust ions (Ca²⁺ and Mg²⁺) 13 h. The ratios of NO₃^- to SO₄^2- were 0.65 in the non-dust period and 0.31 in the dust event. In the dust event, the sulfur oxidation ratio (SOR) was a factor of 1.33 greater than that in the non-dust period, and [SO₄^2-]/[SO₂] was 2.31 times of that in the non-dust period. The source apportionment using Probabilistic Matrix Factorization (PMF) suggested that fugitive dust (58.09%), secondary aerosols (33.98%), and biomass burning (7.93%) were the major sources in the non-dust period whereas dust (67.01%), salt lake (29.68%), biomass burning (0.8%), and motor vehicle (2.51%) were the primary sources in the dust event. Concentration weighted trajectory (CWT) model indicated that NO₃^-, Cl^- and K⁺ could be regarded as local source species, the potential sources of Na⁺, Mg²⁺ and Ca²⁺ concentrated in the two large areas with the one covered in the junction areas of Xinjiang, Qinghai and Gansu and another one covered the places around in Lanzhou, the potential sources of SO₄^2- were mainly localized in the areas adjacent to Lanzhou.

Atmospheric Moisture Pathways to the Highlands of the Tropical Andes: Analyzing the Effects of Spectral Nudging on Different Driving Fields for Regional Climate Modeling

Atmospheric moisture pathways to the highlands of the tropical Andes Mountains were investigated using the Weather Research and Forecasting (WRF) model, as well as back-trajectory analysis. To assess model uncertainties according to the initial and lateral boundary conditions (ILBCs), the effects of spectral nudging and different driving fields on regional climate modeling were tested. Based on the spatio-temporal patterns of the large-scale atmospheric features over South America, the results demonstrated that spectral nudging compared to traditional long-term integration generally produced greater consistency with the reference data (ERA5). These WRF simulations further revealed that the location of the inter-tropical convergence zone (ITCZ), as well as the precipitation over the Andes Mountains were better reproduced. To investigate the air mass pathways, the most accurate WRF simulation was used as atmospheric conditions for the back-trajectory calculations. Three subregions along the tropical Andean chain were considered. Based on mean cluster trajectories and the water vapor mixing ratio along the pathways, the contributions of eastern and western water sources were analyzed. In particular, the southernmost subregion illustrated a clear frequency of occurrences of Pacific trajectories mostly during September–November (40%) when the ITCZ is shifted to the Northern Hemisphere and the Bolivian high pressure system is weakened. In the northernmost subregion, Pacific air masses as well reached the Andes highlands with rather low frequencies regardless of the season (2–12%), but with a moisture contribution comparable to the eastern trajectories. Cross-sections of the equivalent-potential temperature as an indicator of the moisture and energy content of the atmosphere revealed a downward mixing of the moisture aloft, which was stronger in the southern subregion. Additionally, low-level onshore breezes, which developed in both subregions, indicated the transport of warm-moist marine air masses to the highlands, highlighting the importance of the representation of the terrain and, thus, the application of dynamical downscaling using regional climate models.

Characteristics and origins of air pollutants in Wuhan, China, based on observations and hybrid receptor models

To identify the characteristics of air pollutants and factors attributing to the formation of haze in Wuhan, this study analyzed the hourly observations of air pollutants (PM_2.5, PM₁₀, NO₂, SO₂, O₃, and CO) from March 1, 2013, to February 28, 2014, and used hybrid receptor models for a case study. The results showed that the annual average concentrations for PM_2.5, PM₁₀, NO₂, SO₂, O₃, and CO during the whole period were 89.6 μg m^-3, 134.9 μg m^-3, 54.9 μg m^-3, 32.4 μg m^-3, 62.3 μg m^-3, and 1.1 mg m^-3, respectively. The monthly variations revealed that the peak values of PM_2.5, PM₁₀, NO₂, SO₂, and CO occurred in December because of increased local emissions and severe weather conditions, while the lowest values occurred in July mainly due to larger precipitation. The maximum O₃ concentrations occurred in warm seasons from May to August, which may be partly due to the high temperature and solar radiation. Diurnal analysis showed that hourly PM_2.5, PM₁₀, NO₂, and CO concentrations had two ascending stages accompanying by the two traffic peaks. However, the O₃ concentration variations were different with the highest concentration in the afternoon. A case study utilizing hybrid receptor models showed the significant impact of regional transport on the haze formation in Wuhan and revealed that the mainly potential polluted sources were located in the north and south of Wuhan, such as Baoding and Handan in Hebei province, and Changsha in Hunan province.

IMPLICATIONS

Wuhan city requires a 5% reduction of the annual mean of PM_2.5 concentration by the end of 2017. In order to accomplish this goal, Wuhan has adopted some measures to improve its air quality. This work has determined the main pollution sources that affect the formation of haze in Wuhan by transport. We showed that apart from the local emissions, north and south of Wuhan were the potential sources contributing to the high PM_2.5 concentrations in Wuhan, such as Baoding and Handan in Hebei province, Zhumadian and Jiaozuo in Henan province, and Changsha and Zhuzhou in Hunan province.

Identification of long-range transport pathways and potential sources of PM2.5 and PM10 in Beijing from 2014 to 2015

Trajectory clustering, potential source contribution function (PSCF) and concentration-weighted trajectory (CWT) methods were applied to investigate the transport pathways and identify potential sources of PM_2.5 and PM₁₀ in different seasons from June 2014 to May 2015 in Beijing. The cluster analyses showed that Beijing was affected by trajectories from the south and southeast in summer and autumn. In winter and spring, Beijing was not only affected by the trajectories from the south and southeast, but was also affected by trajectories from the north and northwest. In addition, the analyses of the pressure profile of backward trajectories showed that backward trajectories, which have important influence on Beijing, were mainly distributed above 970hPa in summer and autumn and below 950hPa in spring and winter. This indicates that PM_2.5 and PM₁₀ were strongly affected by the near surface air masses in summer and autumn and by high altitude air masses in winter and spring. Results of PSCF and CWT analyses showed that the largest potential source areas were identified in spring, followed by winter and autumn, then summer. In addition, potential source regions of PM₁₀ were similar to those of PM_2.5. There were a clear seasonal and spatial variation of the potential source areas of Beijing and the airflow in the horizontal and vertical directions. Therefore, more effective regional emission reduction measures in Beijing's surrounding provinces should be implemented to reduce emissions of regional sources in different seasons.

Long-range atmospheric transport Beryllium-7 to region the Sea of Japan

Concentrations of cosmogenic beryllium-7((7)Be) and atmospheric aerosols were measured in the atmosphere of the coastal zone of Vladivostok in 2013-2014. The (7)Be concentrations ranged from 0.5 to 4.1 mBq/m(3), with the lowest values in summer and the highest in spring and autumn; the mean value was 2.2 mBq/m(3). Analysis of meteorological data in the synoptic scale showed an inverse correlation with wet deposition rates R = -0.55 (p = 0.0001) and H2O mixing ratio R = -0.49 (p = 0.0001) and a positive with an average maximum height of 120-h backward trajectories of air masses R = 0.65 (p = 0.0001). Angular cluster analysis showed the (7)Be concentration to be dependent on the north-western (R = 0.53, p = 0.001) and eastern winds (R = -0.7, p = 0.0001 for 2013 and R = -0.49, p = 0.002 for 2014). The multiple regression analysis identified five factors in (7)Be concentration: altitudes (b = 0.44), air temperature (b = 0.36), a portion of trajectories in the pacific (North-East direction) cluster (b = -0.32), aerosol concentrations (b = 0.28) and wet precipitation rates (b = -0.24). The model has a good correlation with the data (adjusted R(2) = 0.55). It was found that the direction and height of the air masses trajectories in the lower troposphere strongly influence the concentration of (7)Be.

The role of precursor gases and meteorology on temporal evolution of O₃ at a tropical location in northeast India

South Asia, particularly the Indo-Gangetic Plains and foothills of the Himalayas, has been found to be a major source of pollutant gases and particles affecting the regional as well as the global climate. Inventories of greenhouse gases for the South Asian region, particularly the sub-Himalayan region, have been inadequate. Hence, measurements of the gases are important from effective characterization of the gases and their climate effects. The diurnal, seasonal, and annual variation of surface level O3 measured for the first time in northeast India at Dibrugarh (27.4° N, 94.9° E, 111 m amsl), a sub-Himalayan location in the Brahmaputra basin, from November 2009 to May 2013 is presented. The effect of the precursor gases NO x and CO measured simultaneously during January 2012-May 2013 and the prevailing meteorology on the growth and decay of O3 has been studied. The O3 concentration starts to increase gradually after sunrise attaining a peak level around 1500 hours LT and then decreases from evening till sunrise next day. The highest and lowest monthly maximum concentration of O3 is observed in March (42.9 ± 10.3 ppb) and July (17.3 ± 7.0 ppb), respectively. The peak in O3 concentration is preceded by the peaks in NO x and CO concentrations which maximize during the period November to March with peak values of 25.2 ± 21.0 ppb and 1.0 ± 0.4 ppm, respectively, in January. Significant nonlinear correlation is observed between O3 and NO, NO2, and CO. National Atmospheric and Oceanic Administration Hybrid Single-Particle Lagrangian Integrated Trajectory back-trajectory and concentration weighted trajectory analysis carried out to delineate the possible airmass trajectory and to identify the potential source region of NO x and O3 concentrations show that in post-monsoon and winter, majority of the trajectories are confined locally while in pre-monsoon and monsoon, these are originated at the Indo-Gangetic plains, Bangladesh, and Bay of Bengal.

Radioactive isotopes in atmospheric aerosols over Russia and the Sea of Japan following nuclear accident at Fukushima Nr. 1 Daiichi Nuclear Power Station in March 2011

Artificial radionuclides, such as iodine-131 ((131)I), cesium-134 ((134)Cs), and cesium-137 ((137)Cs), as well as natural isotopes of beryllium-7 ((7)Be) and potassium-40 ((40)K) have been registered in atmospheric aerosols over Vladivostok selected from 11 March to 17 June 2011. Additionally, (134)Cs and (137)Cs were detected in atmospheric aerosols over Tomsk selected from 16 March to 17 June 2011. Artificial radionuclides were also discovered in atmospheric wet depositions sampled in Vladivostok from 3 to 17 May 2011. Moreover, these radionuclides have been registered in atmospheric aerosols over the sea surface of the Sea of Japan selected from 3 to 31 May 2011 during an expedition of the "Nadezhda" sailing ship. From 18 March to 15 April, an increase in concentrations of atmospheric aerosols over Vladivostok from 108.8 to 321.5 μg/m(3) has been registered. It was accompanied by increased activity concentrations of (134)Cs, (137)Cs, and the (131)I. During the period from 18 March to 15 April, activity concentrations of (137)Cs and (134)Cs in atmospheric aerosols increased 100 times compared with the minimum detectable concentration (MDC) level and peaked in the weekly sample gathered from 8 to 15 April (145.0 and 105.3 μBq/m(3), respectively). Variability of concentrations of natural isotopes of (7)Be and (40)K was not greater than 1 order of magnitude throughout the sampling period. Maximal values of (137)Cs and (134)Cs concentrations (1,281.5 ± 141 and 384.4 ± 42.3 μBq/m(3), respectively) in Tomsk were reached in samples taken from 1 to 2 April. For the atmospheric aerosol samples from the Sea of Japan, the largest concentration of (131)I (392.3 ± 215.7 μBq/m(3)) was detected from 13 to 19 May, while all other samples had much lower concentration values. Synoptic analysis of back trajectories movement of air masses showed that the radioactive cloud came to Vladivostok from the regions of Siberia and northeastern part of China. Synoptic analysis for Tomsk showed that during the period of maximal activity concentrations (1-9 April), air masses were arriving from the European part of Russia and north of Kazakhstan.

Analysis of the transport pathways and potential sources of PM10 in Shanghai based on three methods

In this study, we investigated the transport pathways and potential sources of PM(10) in Shanghai based on PM(10) monitoring data recorded from 2006 to 2009 using three methods: backward trajectory cluster analysis, trajectory sector analysis (TSA) and potential source contribution function (PSCF). Seven clusters were generated from the backward trajectory cluster, and two potential sources were identified from the PSCF method. Among the seven clusters, three northerly clusters corresponded to the winter monsoon. The northerly air flow transported high-concentration PM(10) that had been emitted from northwestern sources, including Hebei, Shandong, Anhui and Jiangsu to Shanghai in winter and spring. The other three southerly clusters were associated with the summer monsoon caused by the Indian low and the Subtropical high over the western Pacific Ocean controlling the weather patterns of the eastern coastal area in summer. Corresponding to the southerly path, the PSCF method also identified a southwestern source including Zhejiang, Jiangxi and Fujian. The remaining eastern cluster, which represented the transition of monsoons, did not contribute much to the PM(10) concentration in Shanghai. According to the results of TSA, the relative PM(10) contribution to Shanghai of the northwestern source was approximately twice that of the southwestern source.

The contribution from distant dust sources to the atmospheric particulate matter loadings at XiAn, China during spring

Mass concentration data for PM(10) (particulate matter, PM, less than 10 mum) combined with an air mass back-trajectory clustering technique, a potential source contribution function (PSCF) model, and a concentration-weighted trajectory (CWT) method were used to evaluate the transport pathways and sources of XiAn PM(10) in spring 2001 to 2003. Three dust source areas: "Northwesterly Sources," "Northerly Sources," and a "Loess Plateau Source" and an anthropogenic "Southerly Source" contributing to the high particulate matter concentrations at XiAn were identified using these methods. The CWT method provided more compelling information on dust sources than the PSCF model, but there are clear advantages to using multiple interpretive tools. A comparison of the major dust transport pathways shows differences for XiAn versus Beijing, with "Northwesterly Sources" more important for XiAn and arid and semi-arid regions in Mongolia more important for Beijing.

Peroxyacetyl nitrate in eastern Scotland

Peroxyacetyl nitrate (PAN) concentrations in air were sampled hourly from 1994 to 1998 at a rural site 15 km south-west of Edinburgh, in eastern Scotland. Annual average concentrations were between 0.1 and 0.15 nl l(-1), with episodes up to 3 nl l(-1) in long-range transported polluted air. PAN concentrations were approximately log-normally distributed. The concentrations measured are the result of a balance between photochemical production rates and removal by thermal decomposition and dry deposition. In general, there was a poor correlation between PAN and ozone concentrations at this rural site except during episodes of photochemical pollution, when the PAN/O(3) volume ratio exceeded 0.01. The PAN/NO(x) volume ratio had a median value of 0.015 but ranged up to 0.25. There was a pronounced seasonal maximum in PAN concentrations in late spring, and a strong diurnal cycle only in April-June, with a maximum at 1700 h. Individual episodes, with concentrations up to 3 nl l(-1), could be traced over distances of ca. 1000 km, with rapid changes in concentration as the prevailing winds advected polluted air masses across the site.

METHODS FOR ATTRIBUTING AMBIENT AIR POLLUTANTS TO EMISSION SOURCES

▪ Abstract  Six methods for attributing ambient pollutants to emission sources are reviewed: emissions analysis, trend analysis, tracer studies, trajectory analysis, receptor modeling, and dispersion modeling. The ranges of applicability, types of information provided, limitations, performance capabilities, and areas of active research of the different methods are compared. For primary, nonreactive pollutants whose effects of concern occur on a global scale, an accounting of emissions rates by source type and location largely characterizes source contributions. For other pollutants or smaller spatial scales, accurate estimates of emissions are needed for identifying the emissions reduction potentials of possible control measures and as inputs to dispersion models. Emission levels are frequently known with factor-of-two accuracy or worse, and improved estimates are needed for dispersion modeling. The analysis of regional or urban-scale trends in emissions and ambient pollutant concentrations can provide qualitative information on source contributions, but quantitative results are limited by the confounding influence of variations in meteorology and uncertainties in the areas over which emissions affect concentrations. Tracer studies are useful for quantifying dispersion characteristics of plumes, qualitatively characterizing transport directions, and providing empirical data for evaluating trajectory and dispersion models. Data are usually temporally limited to a short study period, typically do not provide information on vertical pollutant distributions, and are most applicable to the transport of primary, nonreactive pollutants. Trajectory analyses are routinely used to estimate atmospheric transport directions. Trajectory errors of about 20% of travel distance are considered typical of the better models and data sets. Receptor models use measurements of ambient pollutant concentrations to quantify the contributions of different source types to primary particulate matter or volatile organic compounds, or to characterize source-region contributions to a single pollutant. Accuracy rates of ∼30% are often achieved when quantifying the contributions from different types of emission sources. Dispersion models are well-suited for estimating quantitative source-receptor relationships, as the effects of individual emission sources or source regions can be studied. Lagrangian and Gaussian dispersion models are computationally efficient and can simulate the transport of nonreactive primary or linear secondary species. Eulerian models are computationally intensive but lend themselves to the simulation of nonlinear chemistry. Careful evaluation of modeling accuracy is needed for a model application to fulfill its potential for source attribution. Accuracy can be evaluated through a combination of performance evaluation, sensitivity analysis, diagnostic evaluation, and corroborating analyses.