The observation of atmospheric HONO by wet-rotating-denuder ion chromatograph in a coastal city: Performance and influencing factors.

Due to the significance of atmospheric HONO as a reservoir for radicals and the presence of substantial unknown sources of HONO, there is a pressing need for accurate and consistent measurement of its concentration. In this study, we compared the measurements obtained from the monitor for aerosols and gases in ambient air (MARGA) based on wet chemical method with those from the incoherent broadband cavity-enhanced absorption spectroscopy (IBBCEAS) based on optical method to assess the suitability of the MARGA instrument for accurate HONO detection. The diurnal patterns obtained by the two instruments are similar, with peaks at 8 a.m. and lows at 5 p.m. Over the course of the observation period, it was often observed that HONO concentrations recorded by the MARGA instrument consistently exceeded those obtained through the IBBCEAS technique, accounting for approximately 91.33% of the total observation time. Throughout the entire observation period, the R2 value between the two instruments was 0.49, indicating relatively good correlation. However, with a slope of only 0.27, it suggests poor agreement between the two instruments. Furthermore, the R2 and slopes between the two instruments vary with the seasons and day-night. The larger the quartile values of NO2, NH3, and BC, the greater the slopes of both MARGA and IBBCEAS instruments, and the higher the concentrations of NO2, NH3, and BC (indicator of semivolatile oxidizable hydrocarbons), the greater the differences between the two instruments, all indicating that NH3 may promote the reaction of NO2 with semivolatile oxidizable hydrocarbons to produce HONO. The O3 with its strong oxidizing properties may cause underestimation in the MARGA instrument by oxidizing NO2- to NO3- in the absorbing solution. It is challenging to derive a universal correction formula due to the interference of various chemical substances. Hence, MARGA should not be used for HONO research in the future.

Comparative in vitro toxicological effects of water-soluble and insoluble components of atmospheric PM2.5 on human lung cells.

Fine particulates in city air significantly impact human health, but the hazardous compositional mechanisms are still unclear. Besides the toxicity of environmental PM2.5 to in vitro human lung epithelial cells (A549), the independent cytotoxicity of PM2.5-bound water-soluble (WS-PM2.5) and water-insoluble (WIS-PM2.5) fractions were also compared by cell viability, oxidative stress (reactive oxygen species, ROS), and inflammatory injury (IL-6 and TNF-α). The cytotoxicity of PM2.5 varied significantly by sampling season and place, with degrees greater in winter and spring than in summer and autumn, related to corresponding trend of air PM2.5 level, and also higher in industrial than urban site, although their PM2.5 pollution levels were comparable. The PM2.5 bound metals (Ni, Cr, Fe, and Mn) may contribute to cellular injury. Both WS-PM2.5 and WIS-PM2.5 posed significant cytotoxicity, that WS-PM2.5 was more harmful than WIS-PM2.5 in terms of decreasing cell viability and increasing inflammatory cytokines production. In particular, industrial samples were usually more toxic than urban samples, and those from summer were generally less toxic than other seasons. Hence, in order to mitigate the health risks of PM2.5 pollution, the crucial targets might be components of heavy metals and soluble fractions, and sources in industrial areas, especially during the cold seasons.

Meteorological impacts on the unexpected ozone pollution in coastal cities of China during the unprecedented hot summer of 2022.

Surface ozone pollution under climate warming has become a serious environmental issue. In the summer of 2022, abnormal warming spread over most of the Northern Hemisphere and resulted in the abnormal increase in O3 concentrations. In this study, we focused on the coastal cities in China and investigated the O3 trends in July during 2015 to 2022. Four regions with different locations and emission levels were selected for comparison. A significant increase of O3 concentration in July 2022 were observed in the southern coastal cities (16.7-22.8 µg m-3) while the opposite characteristics were found in the northern coastal cities (decrease of 0.26-2.18 µg m-3). The results indicated various distribution patterns of the O3 concentrations responded to heat wave across China. The weakening of East Asian summer monsoon, extension of the western Pacific subtropical high, significant warming, stronger solar radiation, lower relative humidity, less rainfall and sinking motion of atmosphere in 2022 were beneficial for O3 generation and accumulation in the southern coastal areas. Meteorological changes in July 2022 could lead to an increase of 15.6 % in O3 concentrations in southern coastal cities compared to that in 2015-2021, based on the analysis of machine learning. Air temperature was the main contributor to high O3 concentrations in the coast of Fujian province, while other coastal cities depended on relative humidity. This study indicated the challenge of O3 pollution control in coastal areas under global warming, especially in extreme heat wave events.

Sources appointment and health risks of PM2.5-bound trace elements in a coastal city of southeastern China.

To gain a comprehensive understanding of sources and health risks of trace elements in an area of China with high population densities and low PM2.5 concentrations, 15 trace elements (Al, K, Ca, Ti, V, Cr, Mn, Fe, Ni, Cu, Zn, As, Sn, Ba, Pb) in PM2.5 were monitored from December 2020 to November 2021 in a representative city, Xiamen. The concentrations of trace elements in Xiamen displayed an obvious seasonal variation and were dominated by K, Fe, Al, Ca and Zn. Based on Positive Matrix Factorization analysis, source appointment revealed that the major sources of trace elements in Xiamen were traffic, dust, biomass and firework combustion, industrial manufacture and shipping emission. According to health risk assessment combined with the source appointment results, it indicated that the average noncarcinogenic risk was below the threshold and cancer risk of four hazardous metals (Cr, Ni, As, Pb) exceeded the threshold (10-6). Traffic-related source had almost half amount of contribution to the health risk induced by PM2.5-bound trace elements. During the dust transport period or Spring Festival period, the health risks exceeded an acceptable threshold even an order of magnitude higher, suggesting that the serious health risks still existed in low PM2.5 environment at certain times. Health risk assessment reminded that the health risk reduction in PM2.5 at southeastern China should prioritize traffic-related hazardous trace elements and highlighted the importance of controlling vehicles emissions in the future.

New Insights on the Formation of Nucleation Mode Particles in a Coastal City Based on a Machine Learning Approach.

Atmospheric particles have profound implications for the global climate and human health. Among them, ultrafine particles dominate in terms of the number concentration and exhibit enhanced toxic effects as a result of their large total surface area. Therefore, understanding the driving factors behind ultrafine particle behavior is crucial. Machine learning (ML) provides a promising approach for handling complex relationships. In this study, three ML models were constructed on the basis of field observations to simulate the particle number concentration of nucleation mode (PNCN). All three models exhibited robust PNCN reproduction (R2 > 0.80), with the random forest (RF) model excelling on the test data (R2 = 0.89). Multiple methods of feature importance analysis revealed that ultraviolet (UV), H2SO4, low-volatility oxygenated organic molecules (LOOMs), temperature, and O3 were the primary factors influencing PNCN. Bivariate partial dependency plots (PDPs) indicated that during nighttime and overcast conditions, the presence of H2SO4 and LOOMs may play a crucial role in influencing PNCN. Additionally, integrating additional detailed information related to emissions or meteorology would further enhance the model performance. This pilot study shows that ML can be a novel approach for simulating atmospheric pollutants and contributes to a better understanding of the formation and growth mechanisms of nucleation mode particles.

Molecular Composition of Anthropogenic Oxygenated Organic Molecules and Their Contribution to Organic Aerosol in a Coastal City.

Organic aerosols (OA) have gained attention as a substantial component of atmospheric aerosols owing to their impact on atmospheric visibility, climate, and human health. Although oxygenated organic molecules (OOMs) are essential contributors to OA formation, the sources, transformations, and fates of the OOMs are not fully understood. Herein, anthropogenic OOMs (AOOMs), anthropogenic volatile organic compounds (AVOCs), and OA were concurrently measured in Xiamen, a coastal city in southeastern China. Our results show that the AOOMs exhibited a high nitrogen content (76%) and a low oxidation degree. Strong photochemical processes of aromatic VOCs were the predominant sources of AOOMs. Also, NOx concentrations and the occurrence of multigeneration OH radical oxidations were the critical factors that might influence the formation of AOOMs. Finally, the newly developed aerosol dynamic model's results show that more than 35% of the OA mass growth rate is attributed to the gas-particle partitioning of AOOMs. Further sensitivity testing demonstrates that the contribution of AOOMs to OA growth is significantly enhanced during high-particulate-concentration periods, especially under low-temperature conditions. This study emphasizes the vital role of photochemically produced AOOMs derived from AVOCs in OA growth in a coastal urban atmosphere.

Photochemistry in the urban agglomeration along the coastline of southeastern China: Pollution mechanism and control implication.

The concentrations of ground-level ozone (O3) in China have undergone a rapid increase in recent years, resulting in adverse impacts on the air quality and climate change. However, limited research has been conducted on the coastal urban agglomerations with increasingly serious O3 pollution. Therefore, in order to better understand in situ photochemistry, comprehensive field observations of O3 and its precursors, coupled with the model simulation, were conducted in autumn of 2019 at six sites in an urban agglomeration along the coastline of southeastern China. Results indicated that O3 pollution in the southern part of the urban agglomeration was more severe than that in the northern part, due to higher levels of O3 precursors and stronger atmospheric oxidation capacity (AOC) in the southern regions. Oxygenated volatile organic compounds (OVOCs), NO2, and CO dominated the total OH reactivity, and the site-average daytime Ox (O3 + NO2) increments correlated well (R2 = 0.94) with the total OH reactivity of CO and VOCs at these sites except for Quanzhou, where industrial emissions (35.1 %) and solvent usages (33.7 %) dominated the VOC sources. However, vehicle exhausts (31.1 %) were the most predominant contributors to the VOC sources at other sites. The results of model simulations showed that net O3 formation rates were larger at the southern sites. Furthermore, O3 production was mainly controlled by VOCs at most sites, but co-limited by VOCs and NOx at Quanzhou. The most significant VOC groups contributing to O3 formation were aromatics and alkenes, with m/p-xylene, toluene, propene, and ethene being the main contributors at these sites. This study offers a more comprehensive understanding of the characteristics and formation of photochemical pollutions on the scale of the urban areas, indicating the critical need to reduce VOC emissions as a means of mitigating their photochemical effects.

The effect of nitrous acid (HONO) on ozone formation during pollution episodes in southeastern China: Results from model improvement and mechanism insights.

Two ozone (O3) processes, summer episode dominated by local production and autumn episode dominated by regional transport, were chosen to investigate the role of HONO in different pollution processes. Meteorological conditions, diurnal variation of O3, potential source contribution factor (PSCF) analysis, concentration weighted trajectory (CWT) models, and the distribution of the eight-hour maximum values of O3 on mainland China all prove that summer O3 was mainly locally generated while autumn O3 episode was more susceptible to regional transport. The gaps between observations and simulation results with the default HONO chemistry in Master Chemical Mechanism (MCM) of Observation Based Model (OBM) were higher in summer episode (0.58 ppb) than autumn episode (0.37 ppb). Although we implemented nine additional sources in the model to revise the HONO chemistry, the simulated values were still lower than the observed values. HONO promoted O3 production by accelerating the reaction of HO2 + NO and RO2 + NO, and promoted loss of O3 by the reaction of OH + NO2 and RO2 + NO2. The net production rate of O3 with HONO constraint increased by 28.50 % in summer and 22.43 % in autumn, which also indicated that HONO played more important role in the O3 production in summer. The difference of NOx of daily RIR between the cases with and without HONO constraint was higher in summer O3 episode (0.15 %/%) than that in autumn O3 episode (0.09 %/%), the same as to VOCs with -0.20 %/% in summer O3 episode and - 0.14 %/% in autumn O3 episode, which indicated that the presence or absence of the HONO constraint has a greater impact on the RIR value in the case of dominant local generation. In brief, the O3 sensitivity would be more favorable for VOCs without HONO constrained in the model, which would inevitably mislead policy makers to develop efficient policies to control O3 pollution.

Pollution mechanisms and photochemical effects of atmospheric HCHO in a coastal city of southeast China.

Formaldehyde (HCHO) is a vital reactive carbonyl compound, which plays an important role in the photochemical process and atmospheric oxidation capacity. However, the current studies on the quantification of HCHO impacts on atmospheric photochemistry in southeast coastal areas of China with an obvious upward trend of ozone remain scarce and unclear, thus limiting the full understanding of formation mechanism and control strategy of photochemical pollution. Here, systematic field campaigns were conducted at a typical coastal urban site with good air quality to reveal HCHO mechanism and effects on O3 pollution mechanism during spring and autumn, when photochemical pollution events still frequently appeared. Positive Matrix Factorization model results showed that secondary photochemical formation made the largest contributions to HCHO (69 %) in this study. Based on the photochemical model, the HCHO loss rates in autumn were significantly higher than those in spring (P < 0.05), indicating that strong photochemical conditions constrain high HCHO levels in certain situations. HCHO mechanism increased the ROx concentrations by 36 %, and increased net O3 production rates by 31 %, manifesting that the reduction of HCHO and its precursors' emissions would effectively mitigate O3 pollution. Therefore, the pollution characteristics and photochemical effects of HCHO provided significant guidance for future photochemical pollution control in relatively clean areas.

Distinct responses of airborne abundant and rare microbial communities to atmospheric changes associated with Chinese New Year.

Airborne microorganisms, including pathogens, would change with surrounding environments and become issues of global concern due to their threats to human health. Microbial communities typically contain a few abundant but many rare species. However, how the airborne abundant and rare microbial communities respond to environmental changes is still unclear, especially at hour scale. Here, we used a sequencing approach based on bacterial 16S rRNA genes and fungal ITS2 regions to investigate the high time-resolved dynamics of airborne bacteria and fungi and to explore the responses of abundant and rare microbes to the atmospheric changes. Our results showed that air pollutants and microbial communities were significantly affected by human activities related to the Chinese New Year (CNY). Before CNY, significant hour-scale changes in both abundant and rare subcommunities were observed, while only abundant bacterial subcommunity changed with hour time series during CNY. Air pollutants and meteorological parameters explained 61.5%-74.2% variations of abundant community but only 13.3%-21.6% variations of rare communities. These results suggested that abundant species were more sensitive to environmental changes than rare taxa. Stochastic processes predominated in the assembly of abundant communities, but deterministic processes determined the assembly of rare communities. Potential bacterial pathogens during CNY were the highest, suggesting an increased health risk of airborne microbes during CNY. Overall, our findings highlighted the "holiday effect" of CNY on airborne microbes and expanded the current understanding of the ecological mechanisms and health risks of microbes in a changing atmosphere.

Particle number size distribution and new particle formation in Xiamen, the coastal city of Southeast China in wintertime.

New particle formation (NPF) has a great impact on regional and global climate, air quality and human health. This study uses a Scanning Mobility Particle Sizer (SMPS) for simultaneous measurement of particle number size distribution (PNSD) in wintertime to investigate NPF in the coastal city of Xiamen. The mean particle number concentration, surface area concentration and volume concentration were 7.25 × 103 cm-3, 152.54 µm2 cm-3, and 4.03 µm3 cm-3, respectively. Particle number concentration was mainly influenced by the nucleation mode and the Aitken mode, whereas the main contributor to particle surface area concentration and volume concentration was accumulation mode particles. The frequency of NPF events occurred was around 41.4% in December 2019. The typical growth rates of new formed particles were 1.41-2.54 nm h-1, and the observed formation rates were 0.49-1.43 cm-3 s-1. A comparative analysis of conditions between event and non-event days was performed. The results emphasized that air temperature, UV radiation and relative humidity were the most decisive meteorological factors, and NPF events usually occurred under clean atmospheric conditions with low PM concentrations. Although condensation sink was high when NPF event occurred, the level of SO2 and O3 concentration was also high.

A Camel Nose-Inspired Highly Durable Neuromorphic Humidity Sensor with Water Source Locating Capability.

Numerous emerging applications in modern society require humidity sensors that are not only sensitive and specific but also durable and intelligent. However, conventional humidity sensors do not have all of these simultaneously because they require very different or even contradictory design principles. Here, inspired by camel noses, we develop a porous zwitterionic capacitive humidity sensor. Relying on the synergistic effect of a porous structure and good chemical and thermal stabilities of hygroscopic zwitterions, this sensor simultaneously exhibits high sensitivity, discriminability, excellent durability, and, in particular, the highest respond speed among reported capacitive humidity sensors, with demonstrated applications in the fast discrimination between fresh, stale, and dry leaves, high-resolution touchless human-machine interactive input devices, and the real-time monitoring humidity level of a hot industrial exhaust. More importantly, this sensor exhibits typical synapse behaviors such as paired-pulse facilitation due to the strong binding interactions between water and zwitterions. This leads to learning and forgetting features with a tunable memory, thus giving the sensor artificial intelligence and enabling the location of water sources. This work offers a general design principle expected to be applied to develop other high-performance biochemical sensors and the next-generation intelligent sensors with much broader applications.

Source apportionment of PM2.5 and sulfate formation during the COVID-19 lockdown in a coastal city of southeast China.

Revealing the changes in chemical compositions and sources of PM2.5 is important for understanding aerosol chemistry and emission control strategies. High time-resolved characterization of water-soluble inorganic ions, elements, organic carbon (OC), and elemental carbon (EC) in PM2.5 was conducted in a coastal city of southeast China during the COVID-19 pandemic. The results showed that the average concentration of PM2.5 during the city lockdown (CLD) decreased from 46.2 µg m-3 to 24.4 µg m-3, lower than the same period in 2019 (PM2.5: 37.1 µg m-3). Concentrations of other air pollutants, such as SO2, NO2, PM10, OC, EC, and BC, were also decreased by 27.3%-67.8% during the CLD, whereas O3 increased by 28.1%. Although SO2 decreased from 4.94 µg m-3to 1.59 µg m-3 during the CLD, the concentration of SO42- (6.63 µg m-3) was comparable to that (5.47 µg m-3) during the non-lockdown period, which were attributed to the increase (16.0%) of sulfate oxidation rate (SOR). Ox (O3+NO2) was positively correlated with SO42-, suggesting the impacts of photochemical oxidation. A good correlation (R2 = 0.557) of SO42- and Fe and Mn was found, indicating the transition-metal ion catalyzed oxidation. Based on positive matrix factorization (PMF) analysis, the contribution of secondary formation to PM2.5 increased during the epidemic period, consisting with the increase of secondary organic carbon (SOC), while other primary sources including traffic, dust, and industry significantly decreased by 9%, 8.5%, and 8%, respectively. This study highlighted the comprehensive and nonlinear response of chemical compositions and formation mechanisms of PM2.5 to anthropogenic emissions control under relatively clean conditions.

Seasonal and areal variability in PM2.5 poses differential degranulation and pro-inflammatory effects on RBL-2H3 cells.

PM2.5 pollution is a widespread environmental and health problem, particularly in China. Besides leading to well-known diseases in the respiratory system, PM2.5 can also alter immune function to induce or aggravate allergic diseases. To determine whether there are temporal and spatial differences in the allergic responses to PM2.5, monthly samples were collected from four regions (urban, industrial, suburban, and rural areas) through a whole year in Nanjing city, China. Inorganic chemical components (metals and water-soluble ions) of PM2.5 were analyzed, and the rat basophil cells (RBL-2H3) exposed to PM2.5 were assessed through quantitative measures of degranulation (ß-hex and histamine) and pro-inflammation cytokine (IL-4 and TNF-α) expression. The highest levels of ß-hex were measured in winter and spring PM2.5 from urban and industrial areas, or autumn PM2.5 from suburban and rural areas. With respect to histamine, autumn PM2.5 samples were most potent irrespective of the location. Autumn and winter PM2.5 induced higher levels of IL-4 than spring and summer samples. However, spring and autumn PM2.5 caused higher levels of TNF-α. The concentrations of water-soluble ions (NH4+, K+ and Cl-), as well as heavy metals (Pb and Cr), were directly and statistically correlated to the inflammation observed in vitro. In general, the differences between regional and seasonal PM2.5 in stimulating cell degranulation may depend on endotoxin and airborne allergen content of PM2.5. The heavy metals and water-soluble ions in PM2.5 were mostly anthropogenic, which increased the particles' mass-based cellular inflammatory potential, therefore, their health risks, e.g. from vehicular exhaust, coal, and biomass combustion, cannot be ignored.

Air pollution increases human health risks of PM2.5-bound PAHs and nitro-PAHs in the Yangtze River Delta, China.

Identifying the nature and extent of atmospheric PM2.5-bound toxic organic pollutants is beneficial to evaluate human health risks of air pollution. Seasonal observations of PM2.5-bound polycyclic aromatic hydrocarbons (PAHs) and nitro-PAHs (NPAHs) in the Yangtze River Delta (YRD) were investigated, along with criteria air pollutants and meteorological parameters. With the elevated PM2.5 level, the percentage of 4-ring PAHs and typical NPAH including 3-Nitrobiphenyl (3-NBP) and 2-Nitrofluoranthene (2-NFLT) increased by 19-40%. PM2.5-bound 2-NFLT was positively correlated with O3 and NO2, suggesting the contribution of atmospheric oxidation capacity to enhance the secondary formation of NPAHs in the atmosphere. Positive matrix factorization (PMF) analysis indicated that traffic emissions (44.9-48.7%), coal and biomass combustion (27.6-36.0%) and natural gas and volatilization (15.3-27.5%) were major sources of PAHs, and secondary formation (39.8-53.8%) was a predominant contributor to total NPAH concentrations. Backward trajectory analysis showed that air masses from North China transported to the YRD region increased PAH and NPAH concentrations. Compare to clean days, the BaP equivalent concentrations of total PAHs and NPAHs during haze pollution days were enhanced by 10-25 and 2-6 times, respectively. The Incremental Lifetime Cancer Risks (ILCRs) of PAHs by inhalation exposure also indicated high potential health risks in the YRD region. The results implied that the health risks of PM2.5-bound PAHs and NPAHs could be sharply enhanced with the increase of PM2.5 concentrations.

Long-term wet precipitation of PM2.5 disturbed the gut microbiome and inhibited the growth of marine medaka Oryzias melastigma.

Wet precipitation, as an important process of geochemical cycling and the most effective way of cleaning fine atmospheric particles (PM2.5), can introduce the toxic substances in the atmosphere into the water environment. The adverse effect of wet precipitation of PM2.5 on marine fish is still unclear. In this study, PM2.5 samples were collected from six locations along coastal areas of the south China sea for 30 days and used to simulate the impacts of multiday discontinuity wet precipitation of PM2.5 on marine medaka (Oryzias melastigma) in the case of 30 days discontinuity heavy rain (rainfall ≥ 7.6 mm/h and persist 1 h each day). Results showed that wet precipitation of PM2.5 significantly inhibited the body weight gain of fish. In accordance, the size and number of lipid droplets in liver of the exposed groups were lower than those in normal control (NC) group. The expressions of genes involving in lipid degradation including lipoprotein lipase gene (LPL) and carnitine palmitoyltransferase gene (CPT) were up-regulated after exposure. The composition, diversity and function of gut microbiome were affected by wet precipitation of PM2.5. PM2.5 from industrial areas that have higher concentrations of metal profiles show more obvious impacts than PM2.5 from agricultural leisure areas that possessed lower concentrations. All together, the results indicated that wet precipitation of PM2.5 can decrease the diversity of gut microbiome, affect the lipid metabolism, and finally suppress the growth of marine medaka. It confirmed the potential ecological risks of long-term rainfall in air pollution areas to the aquatic organisms.

In-vitro human lung cell injuries induced by urban PM2.5 during a severe air pollution episode: Variations associated with particle components.

Environmental air pollutants pose significant threats to public health, especially the toxicity and diseases caused by the atmospheric fine particulate matters (PM2.5). Since the health risks vary with both the concentrations and compositions of PM2.5 which are determined by aerosol sources, how are their toxic effects relevant to the pollution level becomes an important issue, such as the haze episodes covering clean and polluted days. With the transition from non-pollution to pollution stage, daily PM2.5 samples were collected from both the urban and industrial areas of Nanjing city, eastern China, covering a typical haze event in autumn-winter. Their unpropitious effects on human lung epithelial cells (A549) were compared by in vitro toxicity assays and chemical component analysis. Both air levels and cytotoxic effects of PM2.5 varied with the transition of haze event. Although the concentration of PM2.5 in air is of course the highest in pollution stage driven by local stable meteorological condition, unit mass of them posed higher toxicity (lower cell viability and higher IL-6) but induced lower cell oxidative (evidences of ROS and NQO1 mRNA expression) and inflammatory cytokine TNF-α responses than those particles during non-pollution stage. These patterns were explained by the metals and water-soluble components decreased with the haze development. Non-soluble particulate carbonaceous aerosol compositions might play a significant role in inducing cytotoxicity. Moreover, the regional pattern of episode pollution weakened the spatial variation within a city scale. Since the haze development intensified both the quantity and toxicity of PM2.5 in air, the health risks of overall aerosol exposure were synthetically amplified during haze weather, so the increased air particles with higher toxic components from fuel combustion sources should be key targets of pollution control.

Chemical composition and sources of submicron aerosol in a coastal city of China: Results from the 2017 BRICS summit study.

Chemical compositions of non-refractory submicron aerosol (NR-PM1) were measured via an Aerodyne Aerosol Chemical Speciation Monitor at the coastal city Xiamen during the 2017 BRICS summit from August 10 to September 10. Mean hourly concentration of NR-PM1 was 13.55 ± 8.83 µg m-3 during the study period, decreasing from 18.83 µg m-3 before-BRICS to 13.02 µg m-3 in BRCIS I and 8.42 µg m-3 in BRICS II. Positive matrix factor analyses resolved four organic aerosols (OA): a hydrocarbon-like OA (HOA, 14.78%), a cooking-related OA (COA, 28.21%), a biomass burning OA (BBOA, 18.00%), and an oxygenated OA (OOA, 39.22%). The contributions of local pollutants like nitrate and HOA reduced, while the proportions of sulfate and OOA increased during the control episodes. The diurnal patterns of NR-PM1 species and OA components in each episode were characterized. The results showed that BC, nitrate, COA, and HOA had peaks in the morning and evening, which became less obvious under the emission control. Moreover, the diurnal variations of all species in Ep 3 with emission control were much flatter due to the effect of transport. Backward trajectories analysis confirmed the long-range transport of air masses from the continent, which resulted in the high proportions of sulfate (43.69%) and OOA (50.28%) in Ep 3. Our study implies the significant effect of emission control on reducing primary pollutants, but the formation of particles during the long-range transport need to be paid more attention when set the air quality control strategies in coastal cities.

The cytotoxicity and genotoxicity of PM2.5 during a snowfall event in different functional areas of a megacity.

Atmospheric fine particulate matter (PM2.5) can harm human health, but the chemical composition and toxicity of PM2.5 pollution might vary with weather conditions. In order to investigate the impacts of snowfall weather on aerosol characteristics and toxicity by changing particle sources and components, the daily PM2.5 samples were collected before, during, and after a snowfall event in urban, industrial, suburban, and rural areas of Nanjing city in eastern China, for both chemical composition analysis and cytotoxicity tests. After 24 h exposure to these PM2.5, the cell activity, oxidative stress indicators and inflammatory factor expression levels of human lung epithelial cells A549 were measured by ELISA, and DNA damage was determined by comet assay. Although the concentrations of PM2.5 in the air were reduced during snowfall, they posed stronger cytotoxicity, genetic toxicity and inflammatory responses to A549 cells. Related to the elevated mass concentrations of some components accumulated in PM2.5 during snowfall, As, Co, Cr, Sr, V, water-soluble Na+ and Ca2+ showed positive correlations with toxicity indicators. Therefore, snowfall will clean air by deposition, but also make the PM2.5 components remaining in air mostly anthropogenic by covering ground soil/dust, thus increase the particle's mass-based cytotoxicity and their health risks still cannot be ignored, such as the heavy metals and water-soluble ions from automobile exhaust and coal combustion.

Characteristics of peroxyacetyl nitrate (PAN) in a coastal city of southeastern China: Photochemical mechanism and pollution process.

Peroxyacetyl nitrate (PAN) can effectively indicate photochemical pollution, and also plays a vital role in regional oxidant balance. One-year continuous monitoring of PAN in a coastal city of southeastern China was investigated. The mean concentration of PAN in winter (0.64 ppb) was close to that in autumn (0.73 ppb), indicating that photochemical pollution was still non-negligible in the cold season. The peak occurrence time between O3 and PAN had a delay of 1-2 h in four seasons, due to the rapid decomposition rate of PAN in midday. Emission sources of the precursors are located to the south of the monitoring site, so high concentrations of PAN and O3 are frequently observed under southerly wind conditions. The air mass with low concentration of PAN (0.22-0.34 ppb) and O3 (18.17-23.67 ppb) originated from the ocean with less anthropogenic air pollutants. Continental air mass with high PAN concentration might be related to the contribution of heterogeneous reactions of PM2.5 to the promotion of PAN formation. In the polluted case, PAN concentration was often higher than 1.0 ppb and reached the peak of 4.2 ppb, suggesting the influence of photochemical reactions and local accumulation. High concentrations of HONO and sufficient ultraviolet radiation might be the main factors for rapid photochemical production of PAN. Besides, the lifetime of PAN in winter under the condition of high PM2.5 concentration (≥35 µg·m-3) was up to 3.246 days. This study provided insights into photochemical mechanism and pollution process in a coastal city of southeastern China.