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Due to the local emissions and transportations of air pollution from the most polluted regions such as the North China Plain and Yangtze Delta metropolitan, Xuzhou is becoming one of the most polluted cities in East China. The sources and formation processes of nitrogen-containing aerosols are therefore very complex. Two continuous aerosol measurement campaigns were conducted in this industrial city during the wintertime and summertime of 2016, to investigate the chemical compositions and potential sources of total nitrogen (TN, including 89% inorganic nitrogen and 11% organic nitrogen) in PM2.5. Abrupt enhancements of nitrogen-containing aerosols (e.g., NO3− and NH4+) were found in the winter, and nitrate became as a dominant contributor in high pollution days (e.g., PM2.5 > 150 μg m−3). Nitrogen oxidation ratios (NOR) correlated significantly with aerosol liquid water content (ALWC), which was estimated by ISORPROPIA-II model. This suggested heterogeneous process might be an important pathway in nitrate formation during the high PM2.5 days. The nitrogen isotope composition (δ15N) in TN varied from −1.3 to +13.2‰ with a mean value of 6.9 ± 3.6‰ during the wintertime. An isotope-based source apportionment approach was then developed using a Bayesian isotope mixing model (SIAR) with chemical compositions as an important constrain, which improved accuracy and reduced the overall uncertainties in estimations of TN sources. From this optimized model, we identified six major sources including NH3 from combustion-related emissions (49%), NH3 derived from animal wastes (6%), NH3 from urban volatilization (3%), NOx derived from coal combustion (33%), NOx from biomass burning (5%) and NOx from vehicles (3%). Our results demonstrated that ambient NOx was dominated by coal combustion. Since NOx and NH3 are important precursors for ammonium nitrate aerosols, controlling of combustion related NOx and NH3 emissions might be an important way to reduce PM2.5 levels in this region.

Recently atmospheric brown carbon (BrC) is recognized as an important contributor to light absorption and positive climate forcing. In this work, daily fine particulate matter (PM2.5) samples were collected over a full year (May 2015–May 2016) in Nanjing, and seasonal light absorption properties of water-soluble BrC were investigated. We found that winter samples had the strongest light absorption among four seasons. The light absorption at 365 nm (Abs365) for all seasons linked closely with secondary organic carbon (SOC), indicating a dominant contribution from secondary sources to BrC. However primary biomass burning might also contribute to BrC as revealed by the good correlations of Abs365 versus levoglucosan fragments and/or K+, and such influence was more evident during summer. Furthermore, an Aerodyne soot-particle aerosol mass spectrometer (SP-AMS) was employed to determine the elemental ratios of BrC. We found that except in winter, the Abs365 in general positively correlated with the average oxidation states (OSc) of BrC, suggesting more BrC were produced at higher OSc. The mass absorption efficiency at 365 nm (MAE365) showed no clear dependences on OSc during spring, summer and fall, but decreased against OSc during winter, indicating chemical aging may lead to photo-bleaching of BrC in winter. Moreover, positive responses of Abs365 and MAE365 to N/C ratios were found during all seasons, indicating nitrogen-containing organics can be important BrC chromophores. Potential source areas of BrC were further discussed to improve our understanding of BrC sources in this region.

Ammonium (NH4+) is a well-known alkaline species for haze formation and possesses potential impacts on human health and biological diversity. To date, regional source apportionments of NH4+ have been poorly understood in Northern China Plain (NCP). In this study, daily PM2.5 samples were synchronously collected in eight cities over the NCP region. In addition to water-soluble ions, the nitrogen isotopic composition of NH4+ (δ15N–NH4+) was also analyzed. The average concentrations of NH4+, a targeted species, varied from 0.9 μg/m³ to 42.5 μg/m³. Note that the significant enhancements of NH4+ coincided with increasing PM2.5 masses, suggesting that NH4+ was one of the contributing species for haze formation. The δ15N–NH4+averaged 12.4 ± 6.9‰ and the average δ15N–NH3 were further calculated to be −9.0 ± 6.7‰ over the NCP region. Both δ15N–NH4+ and δ15N–NH3 showed negative correlations with PM2.5 mass and there were no obvious differences among those 8 cities. Combining air-mass backward trajectories and quantifying contributions of potential sources, we pointed out that non-agricultural sources (fossil fuel related and NH3 slip) were dominant sources (totally contributed 42%–85%) not only on extreme haze phase but also on haze accumulation/dissipation phase in all 8 cities of NCP region in winter, the heating season in North China. However, the contribution of fossil fuel related source reduced to only 20%–35% while livestock breeding source rose to about 15%–32% and NH3 slip source kept contributing about 30% on the extreme haze phase. Thus, we considered that volatilization-related agricultural sources (especially livestock breeding) could discharge considerable NH3 to form SIA-led haze event in urban cities of the NCP region, even though non-agricultural sources were the foremost sources.

To fully identify the formation and source characteristics of aerosol nitrate during winter which accompanied by frequent haze in Northeast China, the nitrate concentrations, δ15N–NO3- and δ18O–NO3- characteristics of PM2.5 samples from four sites of different types including the (a) urban area, (b) suburban area, (c) suburban-rural transition area and (d) rural area in Northeast China were analyzed in this work. δ15N isotope fractionation (eN) during the conversion of atmospheric NOX (δ15N-NOX) to nitrate (δ15N–NO3-) was discussed on the basis of the estimated contributions of the gas phase oxidation pathway of OH radical (·OH) (γOH) and the heterogeneous hydrolysis pathway of N2O5 (γN2O5) to nitrate formation. Besides, the contribution of biological soil, coal combustion, biomass burning and motor vehicles to NOX emissions had also been analyzed using Bayesian isotope mixing model. Results showed that different types of sites had inconsistent source contributions. Obviously, coal combustion plays an absolutely indispensable role in the production of NOX in all the sites, especially in rural areas (d), where coal combustion contributed up to 89.8%. In addition, biomass burning still has a great effect on NOX emissions in the Northeast, showing a contribution of 5.2%–35.8%. It is worth noting that in urban site (a) where the tropospheric O3 concentration (34±9 μg m−3) was significantly lower than the other regions ((b): 54 ± 16 μg m−3, (c): 101 ± 21 μg m−3, (d): 98 ± 17 μg m−3), the contribution of the ·OH pathway to nitrate was as high as 69.4%, which was very different from the other three sites. The different formation mechanisms of nitrate in urban and non-urban may be due to different O3. Haze not only affects the sources of nitrate, but also changes the contribution of nitrate formation. Except for rural site (d), the contribution of the heterogeneous reaction (N2O5 pathway) of the other three sites during the haze period was greater (a: 35.1%, b: 60.0%, c: 59.0%, d: 60.8%) than in the non-haze period (a: 22.5%, b: 44.7%, c: 41.9%, d: 64.2%).

Taxi drivers and passengers are exposed to high levels of traffic-related air pollutants, but their exposures to fine (PM2.5) and ultrafine particles (UFPs) and related mitigation strategies are rarely explored. In this study, UFP and PM2.5 concentrations were monitored concurrently inside and outside of 22 taxis under different ventilation and mitigation conditions. Under realistic working conditions (no mitigation; NM), the average UFP and PM2.5 levels inside taxis were 1.46 × 104 particles/cm3 and 26 μg/m3, respectively. When the taxi ventilation was set to outside air mode and the windows kept closed, in-cabin UFP and PM2.5 concentrations are significantly associated with on-road concentrations, driving speed, and cabin air filter usage. The average in-cabin to on-roadway (I/O) ratios for UFP and PM2.5 were reduced from 0.60 to 0.75 under NM, to 0.47 and 0.52 under the most stringent mitigation strategy of keeping the windows closed and operating a high efficiency cabin air filter (WC + HECA). Among all tested taxi models, Toyota Prius exhibited the lowest UFP and PM2.5 I/O ratios under WC + HECA. Switching cabin air filters from the originally equipped manufacturer filter (OEM) to a HECA filter reduced the UFP and PM2.5 I/O ratios most effectively in Toyota Prius taxis as well.

Chiang Mai suffers from adverse haze associated with heavy biomass burning (BB) during almost every dry season (February to April). As an important source of light-absorbing carbonaceous aerosols (black carbon and brown carbon), BB can have strong radiative effects on local and regional climate. However, studies on characterizing the impacts of BB aerosols on climate in Chiang Mai are quite limited. In this study, we use a global chemical transport model (GEOS-Chem) coupled with the rapid radiative transfer model for GCMs (RRTMG) to estimate the radiative forcing (RF) of BB aerosols in Chiang Mai. Brown carbon (BrC) is included as an absorber and treated as an individual tracer in the model. To our best knowledge, this is the first study to estimate the BrC RF in Chiang Mai. As evaluated, our simulations that were assigned with medium- and high-absorbing kBrC (BrC imaginary refractive index) well reproduces the absorption coefficient of ambient BrC in Chiang Mai. Based on our estimations, 33–40% of total carbonaceous aerosol absorption at 440 nm is attributed to BrC and 60–67% to BC during dry season. As estimated, BrC contributes 14 ± 3% to the instantaneous RF of total carbonaceous aerosol (IRFCAs) at the top of atmosphere (TOA) and 16 ± 3% to IRFCAs at surface. Moreover, including BrC in model strengthens (reduces) the surface (TOA) cooling effect of total organic carbon by 9 ± 5% (9 ± 3%), indicating the warming effect of BrC in the atmosphere in Chiang Mai.

Haze pollution occurs frequently over northern China Plain (NCP) during winter, resulting in great threats to human health. So far, limited studies have linked between emission sources and health risks from ambient field measurements. In this work, PM2.5 samples were collected in Beijing in the 2018 winter; 23 metallic elements were determined to assess the health risks induced by PM-bound metals. During the sampling period, metallic elements constituted a minor fraction (5%) in PM2.5, but exhibited significant threats to human health. The cancer risk (CR) value induced by PM-bound metals was 1.41 × 10−4 for adults and 2.59 × 10−4 for children while non-cancer risk (NCR) was 2.59 for adults and 3.37 for children. Nickel (Ni), As and Cr(IV) were the major contributing elements to carcinogenic risk. Arsenic (As) contributed a major (57%) of NCR for children, and Mn (30%), Ni (27%) and As (24%) were the major contributing species to NCR for adults. Using positive matrix factorization (PMF) model, traffic-related emission (25% for children and 30% for adults) and heavy oil combustion (39% for children and 28% for adults) were the dominant sources of CR values. Moreover, the CR value induced by local emissions was higher than that by long-range transported air pollution. Local traffic emission and long-range transported heavy oil combustion enhanced CR values, threatening the human health. As results, we highlighted that control of traffic emissions and heavy oil combustion on local and regional scales should be seriously considered by the Chinese government in reduction of health risk in Beijing.

Radiocarbon ( 14 C) analysis is a unique tool that can be used to directly apportion organic carbon (OC) and elemental carbon (EC) into fossil and non-fossil fractions. In this study, a coupled carbon analyzer and high-vacuum setup was established to collect atmospheric OC and EC. We thoroughly investigated the correlations between 14 C levels and mass recoveries of OC and EC using urban PM 2.5 samples collected from a city in central China and found that: (1) the 14 C signal of the OC fraction collected in the helium phase of the EUSSAR_2 protocol (200 °C for 120 s, 300 °C for 150 s, 450 °C for 180 s, and 650 °C for 180 s) was representative of the entire OC fraction, with a relative error of approximately 6%, and (2) after thermal treatments of 120 s at 200 °C, 150 s at 300 °C, and 180 s at 475 °C in an oxidative atmosphere (10% oxygen, 90% helium) and 180 s at 650 °C in helium, the remaining EC fraction sufficiently represented the 14 C level of the entire EC, with a relative error of 14 C analysis was 64± 7% (n = 5) and 87 ± 5% (n = 5), respectively. The fraction of modern carbon in the OC and EC of reference material (RM) 8785 was 0.564 ± 0.013 and 0.238 ± 0.006, respectively. Analysis of 14 C levels in four selected PM 2.5 samples in Xinxiang, China revealed that the relative contribution of fossil sources in OC and EC in the PM 2.5 samples were 50.5± 5.8% and 81.4± 2.6%, respectively, which are comparable to findings in previous studies conducted in other Chinese cities. We confirmed that most urban EC derives from fossil fuel combustion processes, whereas both fossil and non-fossil sources have comparable and important impacts on OC. Our results suggested that water-soluble organic carbon (WSOC) and its pyrolytic carbon can be completely removed before EC collection via the method employed in this study.

To determine the causes of a severe haze episode in January 2013 in China, a source apportionment of different carbonaceous aerosols (CAs) was conducted in a megacity in central China (Wuhan, Hubei Province) by using the measurements of radiocarbon and molecular organic tracers. Non-fossil sources (e.g., domestic biofuel combustion and biogenic emissions) were found to be responsible for 62% ± 5% and 26% ± 8% of organic carbon (OC) and elemental carbon (EC) components by mass, respectively. Non-fossil sources contributed 57% ± 4% to total CAs in this large-scale haze event, whereas fossil-fuel sources were less dominant (43% ± 4%). The CAs were composed of secondary organic carbon (SOC; 46% ± 10%), primary fossil-fuel carbon (29% ± 4%) and primary biomass-burning carbon (25% ± 10%). Although SOC was formed mainly from non-fossil sources (70% ± 4%), the role of fossil precursors was substantial (30% ± 4%), much higher than at the global scale. Combined measurement of organic tracers and radiocarbon showed that most non-fossil SOC was probably derived from biomass burning during this long-lasting haze episode in central China.

Nitrated polycyclic aromatic hydrocarbons (NPAHs) are strong environmental mutagens and carcinogens originating from both primary emissions and secondary reactions in the atmosphere. The sources and the toxicity of different NPAH species could vary greatly; therefore a specie-specific source apportionment is essential to evaluate their health risks and to formulate controlling regulations. However, few studies have reported source apportionment of NPAHs species to date. In this study, we developed an easy-to-perform method for the apportionment of primary versus secondary sources of airborne NPAHs based on the relationship between NPAHs and NO 2 . After log-transformation of both NPAHs and NO 2 concentrations, a slope of β between these two variables was obtained by the linear regression. When β is significantly smaller than 1, it indicates primary emissions while β significantly greater than 1 suggests secondary formation. We have validated this method with data previously collected in Beijing. A good correlation, with R value of 0.57, was observed between results produced by this new method and by Positive Matrix Factorization (PMF). The correlation could be further improved (R = 0.71) if the gas/particle partition of NPAHs is taken into consideration. This developed method enables the source apportionment for individual NPAHs species and could be used to validate the results of other receptor models.

In recent years, there are still huge amounts of NOx emissions in the Northeast, and this inevitably increases the concentration of aerosol nitrate (NO3−), which plays an important role in atmospheric pollution. Because of the mixed complicated sources of atmospheric NO3−, it is difficult to quantify their contribution, and the use of certain means to identify their sources and pathways is critical to developing effective control measures. Since different sources of NOX have different ranges of δ15N values, δ15N is considered to be a useful tool for identifying the source of aerosol NO3−. But isotope fractionation is produced during the conversion of NOX to NO3−, and δ18O can be used to estimate its isotope fractionation value. In this study, daily PM2.5 samples were collected in four seasons from Northeast China, and their water-soluble ionic components (WSIs), δ15N–NO3- and δ18O–NO3- were analyzed. The isotope fractionation value of δ15N in which NOX was converted to NO3− was estimated and the contribution of different sources was quantified in combination with the Bayesian model. The results showed that NO3− was the most important inorganic ion component in the WSIs with the highest annual average ratio of 21.1%. Both δ15N and δ18O showed higher in winter (δ15N: 13.79‰±2.17‰; δ18O: 70.50‰±10.02‰) than in summer (δ15N: 2.69‰±2.95‰; δ18O: 58.67‰±4.52‰). The daytime OH pathway was considered to play a leading role in nitrate formation, with the annual average contribution of 61.0 ± 18.8%. NOx was mainly from the contribution of coal combustion (34.5%) and biomass burning (34.3%) followed by traffic (19.5%) and biological soil (11.7%). During heating periods, NOx was dominated by coal combustion with the average contribution of 46.9% whereas biomass burning was the most important contributor during non-heating periods (39.5%). Therefore, controlling coal consumption and biomass burning can drastically reduce concentration of aerosol NO3− in Northeast China.

We examined the characteristics and source apportionment of organic aerosols in ambient PM2.5 samples collected during the late autumn in Changchun, Northeast China. 8 compound classes (>90 individual species) were detected in the aerosol samples, including biomass burning tracers, aliphatic lipids (fatty acids and fatty alcohols), secondary oxidation products, polycyclic aromatic hydrocarbons (PAHs), sugar compounds, hopanes and biogenic secondary organic aerosol (SOA) tracers. The concentrations of total quantified organic species ranged from 138.2 to 6.8 × 103 ng m−3, among which levoglucosan was the most abundant compound. Biomass burning tracers (anhydrosugars, lignin and resin acids) were the most abundant compounds, followed by fatty acids, secondary oxidation products, PAHs, sugar compounds and fatty alcohols. Biogenic SOA tracers and hopanes were less abundant. The homohopane index [defined as 31abS/(31abS + 31abR)] was 0.5, indicating a potential contribution of traffic emission. PAHs showed a dominance of benzo(b)fluoranthene (BbF), and the diagnostic ratios implicated a substantial contribution of petroleum combustion as well as coal combustion. 2-methylglyceric acid to 2-methyltetrols ratio (2.2) indicated that NOx influence isoprene oxidation products formation. Furthermore, the average ratio of cis-pinonic acid plus pinic acid to 3-hydroxyglutaric acid (31.4) revealed the much fresher α/β-pinene oxidation products to some extent. A good correlation was found between β-caryophyllinic acid and levoglucosan (r = 0.61), suggesting that β-caryophyllene can mainly be generated by biomass burning. The biogenic secondary organic carbon (SOC) was underestimated by the tracer-based method, which only occupied 0.4% of the organic carbon (OC). In contrast, PMF model indicated that emissions from fossil fuel combustion and biomass burning were most important, accounting for 42.4% and 33.6%, respectively, followed by biogenic SOA emission (17.0%) and fungal spore derived source (7.0%), suggesting biogenic aerosol is a nonnegative contributor. Capsule Fossil fuel combustion (42.4%) as well as biomass burning (33.6%) were most important contributors of organic aerosols in a typical city in Northeast China.

In urban China, human excreta are mostly stored in septic tanks beneath various buildings, and the generated NH3 are emitted to the atmosphere through ceiling ducts on rooftops. Here we performed highly time-resolved measurements of NH3 concentrations and auxiliary parameters in the ceiling duct of a typical building complex during different seasons with varying temperature and population, allowing an in-depth investigation of the driving forces in terms of governing NH3 emissions. Extremely high levels of NH3 concentration (1013 ± 793 μg m−3) were observed throughout the campaign. Seasonally, the NH3 concentration during summer vacation (1377 ± 1072 μg m−3) was significantly higher than during school time in fall (796 ± 432 μg m−3) and winter (661 ± 267 μg m−3). Moreover, the diurnal variation of NH3 during summertime was highly correlated with temperature (R2 = 0.95, p m e a n m i n m a x ) ‰ to − 35.6 ‰ − 39.8 ‰ − 31.9 ‰ . These results support that temperature is the key factor in controlling NH3 emissions from human excreta and demonstrate the importance of using human excreta emitted δ15N–NH3 to quantify excreta NH3 contribution in urban atmospheres. Our findings highlight opportunities to limit NH3 emissions from human excreta that will bring co-benefits to the air quality and human health in urban China.

Residential solid fuel combustion (RSFC) is a major contributor to polycyclic aromatic hydrocarbons (PAHs) in the atmosphere, which are strongly related to negative health impacts. During RSFC, the variations of PAH emission factors (EFs) and size-resolved profiles are known to be highly affected by fuel type and combustion temperature. In this study, to investigate the behavior of emitted PAH, combustion experiments were performed using three wood and three coal types under different temperatures (500 °C and 800 °C) in a quartz tube furnace. The results show that the average EFs of PAH (17-EPA-PAHs) from low temperature coal combustion were nearly three times higher than those from low temperature wood combustion. However, with high temperature, PAH emissions from wood combustion increased two-fold and that from coal combustion decreased by two orders. Furthermore, And the proportion of high-molecular-weight PAHs (HPAHs) increased with increasing temperature in wood combustion, but decreased in coal combustion. This indicates that PAH synthesis was the dominant process during wood combustion, while pyrolysis of coal supramolecular structure was the main formation pathway of PAH during coal combustion. In addition, more low-molecular-weight PAHs (LPAHs) were emitted, with 0.006 μm–0.050 μm and 0.223 μm–1 μm particles in the early burning stage, while more HPAHs were emitted in the later burning stage, with larger particles in the size range of 0.050 μm–0.223 μm. This means that the PAH formations were different during each burning stage.

Secondary inorganic aerosols, including sulfate, nitrate, and ammonium (SNA), are the predominant components of fine particles (PM2.5). Reasonable representations of SNA formation in numerical models can largely improve the predictions of PM2.5 concentrations and effectively help implement emission control strategies. Despite the Atmospheric Pollution Prevention and Control Action Plan has been implemented since 2013, PM2.5 concentration during 2017 in Nanjing, one of the megacities in China, still exceeded the World Health Organization-recommended safe level (35 μg m−3). In this study, WRF-Chem model was applied to simulate aerosol chemical components in PM2.5 during April 2016 and January 2017 in Nanjing, and the simulations are evaluated with in-situ observations. Our results show that the model can reasonably reproduce the temporal variability of PM2.5 in two seasons, but significantly underestimate the sulfate concentrations by 71% (84%) in April (January), and overestimate the nitrate concentrations by 67% (45%) in April (January). The simulated ammonium is overall consistent with the observations. Meanwhile, the model tends to overestimate SO2 concentrations by 20% (74%) in April (January). Several sensitivity studies are conducted to explore the mechanisms for underestimation of sulfate and overestimation of nitrate, and found that the conversion rate of SO2 to sulfate is significantly underestimated in the model. Tripling the gas-phase oxidation rate of SO2 by OH only enhances sulfate by 67% (72%) in April (January), indicating gas-phase oxidation is not the main causes for the underestimations in the model. However, inclusion of SO2 heterogeneous oxidation in aerosol water can largely increase the simulated sulfate by 84% (196%) in April (January), and also better reproduce the diurnal variations of sulfate compared to the reference run. It should be noted that the simulated sulfate is still 47% (53%) lower than the observations in April (January), though inclusion of heterogeneous reaction can substantially improve the simulation performance of SNA.

A loading dock is a common functional component of modern commercial and institutional buildings where substantial amount of air pollutants might be emitted by diesel trucks. This study aims to determine whether pollutants in a loading dock could infiltrate into nearby indoor environments through mechanic ventilation systems. We measured the levels of fine particulate matter (PM2.5) and black carbon (BC), and particle size distributions at a loading dock and inside three offices of a nearby building. We observed increased levels of PM2.5 and BC both at the loading dock and in the offices due to trucking activities. The infiltration factors (Fin), defined as the equilibrium fraction of outdoor particles that penetrates indoors, were greater for BC (range: 0.20–0.24) as compared with PM2.5 (range: 0.02–0.13) and were greater for larger particles in the size range of 7.64–289 nm. To reduce human exposures to those particles, an anti-idling policy was implemented at the loading dock as part of the study. As a result, the levels of PM2.5 and BC were significantly (p

Radiocarbon ( 14 C) measurement of water-soluble organic carbon (WSOC) in ambient aerosols is a quantitative tool for unambiguously distinguishing fossil and non-fossil sources. In this study, a fast and reliable method for measuring 14 C in micro-scale (mg) WSOC aerosol samples is successfully developed, which includes three steps: (1) extraction (2) freeze drying, and (3) online 14 C analysis of CO2 from WSOC combustion. Procedure blanks are carefully assessed by measuring high-purity water and reference materials. Accurate 14 C results could be obtained for WSOC with only 10 mg C, and thus the potential applications are substantially broadened because much less filter material is needed compared to pre- vious reported methods. This method is applied to aerosols samples collected during winter from Switzerland and China. The results demonstrate that non-fossil sources are important if not dominant contributors of WSOC. These non-fossil components are consistently enriched in WSOC compared to bulk OC and water-insoluble OC for all samples, due to high water solubility of primary and secondary biomass burning aerosols. However, the presence of fossil WSOC is still considerable indicating a sub- stantial contribution of secondary OC (SOC) formed from precursors emitted by fossil emissions. Larger fossil contributions to WSOC is found in China than in Switzerland and previously reported values in Europe, USA and South Asia, which may be attributed to higher fossil-derived SOC formation in China. © 2014 Published by Elsevier Ltd.

Air samples were collected from Jan 16 to Mar 14, 2008 onboard the Oceanic II- The Scholar Ship which navigated an east–west transect from Shanghai to Cape Verde, and polybrominated diphenyl ethers (PBDEs) were analyzed in these samples. PBDE concentrations in the atmosphere over the open seas were influenced by proximity to source areas and land, and air mass origins. The concentrations of Σ21PBDEs over the East and South China Seas, the Bay of Bengal and the Andaman Sea, the Indian Ocean, and the Atlantic Ocean were 10.8 ± 6.13, 3.22 ± 1.57, 5.12 ± 3.56, and 2.87 ± 1.81 pg m−3, respectively. BDE-47 and -99 were the dominant congeners in all the samples, suggesting that the widely used commercial penta-BDE products were the original sources. Over some parts of Atlantic and Indian Ocean, daytime concentrations of BDE-47 and BDE-99 were higher than the concentrations at night. The strong atmospheric variability does not always coincide with a diurnal cycle, but the variability in air concentrations in such remote areas of the ocean remains strong. No significant trends were found for each of PBDE congener with latitude.

In order to investigate the chemical characteristics and sources of organic acids in precipitation in Southwest China, 105 rainwater samples were collected at a semi-urban site in Anshun from June 2007 to June 2008. Organic acids and major anions were analyzed along with pH and electrical conductivity. The pH values varied from 3.57 to 7.09 for all the rainfall events sampled, with an average of 4.67 which was typical acidic value. Formic, acetic and oxalic acids were found to be the predominant carboxylic acids and their volume weighted average (VWA) concentrations were 8.77, 6.93 and 2.84 μmol l −1 , respectively. These organic acids were estimated to account for 8.1% to the total free acidity (TFA) in precipitation. The concentrations of the majority organic acids at studied site had a clear seasonal pattern, reaching higher levels during the non-growing season than those in growing season, which was attributed to dilution effect of heavy rainfall during the growing season. The seasonal variation of wet deposition flux of these organic acids confirmed higher source strength of biogenic emissions from vegetation during the growing season. Formic-to-acetic acids ratio (F/A), an indicator of primary versus secondary sources of these organic acids, suggested that primary sources from vehicular emission, biomass burning, soil and vegetation emissions were dominant sources. In addition, the lowest concentrations of organic acids were found under type S, when air masses originated from the marine (South China Sea) during Southern Asian Monsoon period. And the highest concentrations were observed in precipitation events from Northeast China (type NE), prevailing mostly during winter with the lowest rainfall.