Search

Source apportionment of organic carbon (OC) and elemental carbon (EC) from PM 1 (particulate matter with a diameter equal to or smaller than 1 μm) in Beijing, China was carried out using radiocarbon ( 14 C) measurement. Despite a dominant fossil-fuel contribution to EC due to large emissions from traffic and coal combustion, nonfossil sources are dominant contributors of OC in Beijing throughout the year except during the winter. Primary emission was the most important contributor to fossil-fuel derived OC for all seasons. A clear seasonal trend was found for biomass-burning contribution to OC with the highest in autumn and spring, followed by winter and summer. 14 C results were also integrated with those from positive matrix factorization (PMF) of organic aerosols from aerosol mass spectrometer (AMS) measurements during winter and spring. The results suggest that the fossil-derived primary OC was dominated by coal combustion emissions whereas secondary OC was mostly from fossil-fuel emissions. Taken together with previous 14 C studies in Asia, Europe and USA, a ubiquity and dominance of nonfossil contribution to OC aerosols is identified not only in rural/background/remote regions but also in urban regions, which may be explained by cooking contributions, regional transportation or local emissions of seasonal-dependent biomass burning emission. In addition, biogenic and biomass burning derived SOA may be further enhanced by unresolved atmospheric processes.

To better characterize the chemical compositions and sources of fine particulate matter (i.e. PM 2.5 ) in Sanjiang Plain, Northeast China, total carbon (TC), organic carbon (OC), elemental carbon (EC), water-soluble organic carbon (WSOC), and inorganic ions as well as stable carbon isotopic composition (δ 13 C) were measured in this study. Intensively open biomass burning episodes are identified from late September to early October by satellite fire and aerosol optical depth maps. During the biomass-burning episode, concentrations of PM 2.5 , OC, EC, and WSOC are increased by a factor of 4-12 compared to those during the non-biomass-burning period. Non-sea-salt potassium is strongly correlated with PM 2.5 , OC, EC and WSOC, demonstrating an important contribution from biomass-burning emissions. The enrichment in both the non-sea-salt potassium and chlorine is significantly larger than other inorganic species, suggesting that biomass-burning aerosols in Sanjiang Plain are mostly fresh and less aged. In addition, the WSOC-to-OC ratio is lower than that reported in biomass-burning aerosols in tropical regions, further supporting that biomass-burning aerosols in Sanjiang Plain are mostly primary and secondary organic aerosols may be not significant. A lower average δ 13 C value (-26.2‰) is observed during the biomass-burning period, indicating a dominant contribution from combustion of C3 plants in the studied region., (Copyright © 2015. Published by Elsevier B.V.)

To study the role of biomass burning (BB) in air pollution at upper‐northern Thailand, the source apportionment of size‐resolved carbonaceous aerosols from Chiang Mai was carried out based on the radiocarbon (14C) analysis. The fraction of modern carbon (F14C) was generally decreased with particle size increasing and with the highest and lowest values of 0.90 ± 0.04 and 0.61 ± 0.04, respectively. Elemental carbon, regardless of emission sources, and BB‐derived organic carbon (OCbb) showed unimodal size distribution patterns with peaks at 0.43–0.65 μm. Fossil‐fuel derived‐OC (OCf) displayed a bimodal mode with the major peak at 2.1–10 μm, and the minor one at 0.43–0.65 μm. The biogenic secondary organic aerosols (BSOA) showed a typical fine‐mode unimodal size distribution pattern during the high BB (HBB) season, and a bimodal mode during the low BB season. The BSOA concentration increased by 189% ± 80% due to the interaction with open BB plums during HBB season, which was quantified by a 14C‐involved random forest model. Besides, the concentration of biogenic primary organic aerosols also showed a significant increment during the HBB season, especially in sub‐microns. Our results highlight the critical importance of controlling open fires to reduce air pollutants and the potential exposure risk. Plain Language Summary: Large‐scale biomass burning (BB) activities take place annually in Southeast Asia. BB can emit large amounts of carbonaceous aerosols (CA) thus affecting human health and causing climate change. The particle size, directly affects how deep the particle can penetrate the human body, can be significantly changed by BB. In this study, BB‐derived CA contributed the most to the total concentration of CA. The concentration of BB‐derived CA in PM10 (particles with an aerodynamic diameter of less than 10 μm) was 12 times higher in high BB (HBB) season than in low BB (LBB) season. More specifically, BB‐derived CA in fine (PM1.1) and coarse (PM1.1–10) particles increased by roughly 13 and 5 times in HBB season compared to LBB season, respectively. Besides, BB enhanced the concentration of biogenic secondary organic aerosols by 180%, wherein 65% of the increment was allocated in PM1.1. Our results indicated that BB can not only emit particles or precursors of aerosol particles but also promote the generation of biogenic aerosols. And BB significantly enhanced the loading of CA, particularly in fine particles. Key Points: Fossil‐derived carbonaceous aerosols (CA) showed a bimodal mode size distribution patternNon‐fossil‐derived CA showed a typical fine‐mode unimodal size distribution patternBiomass burning greatly enhanced the production of biogenic secondary organic aerosols particularly in fine aerosols [ABSTRACT FROM AUTHOR]

The influence of continental emissions on the origin and formation mechanisms of atmospheric particulate nitrate (ρ‐NO3−) aerosols in the marine boundary layer remains unclear. Here, synchronous observations of nitrogen isotope ratios (δ15N–NO3−) and oxygen isotope anomaly (Δ17O–NO3−) in ρ‐NO3− were conducted across the Yellow Sea and Bohai Sea in Eastern China. Nitrate concentrations, δ15N–NO3− and Δ17O–NO3− exhibited a pronounced north‐to‐south latitudinal gradient. Combined with backward air mass trajectory analysis, the high nitrate concentration and isotopic characteristics in the northern sea area were found to be affected by the continental outflow near China while the low values in the southern sea area were more related to the oceanic inflow. Stable isotope analysis in R (SIAR) indicated that near the northern sea area, the nitrate radicals (NO3) reacted with hydrocarbons (HC) or dimethyl sulfides (DMS) pathway (NO3 + HC/DMS) played a leading role in nitrate production, whereas the NO2 + OH pathway dominated near the southern sea area. Nitrate in the northern seas originated mainly from nitrogen oxides (NOx = NO + NO2, the gaseous precursor of nitrate) emitted from continental sources, especially coal combustion and biomass burning. While closer to the southern seas, the proportion of NOx generated in the marine environment (from ship and biogenic emissions) increased. Overall, the differential relative contributions of continental and marine atmospheric chemistry and NOx sources lead to the spatial distribution characteristics of atmospheric nitrate concentrations and isotopic values over the Yellow and Bohai Seas. Plain Language Summary: This study investigated the impact of emissions from land sources on the formation of nitrate particles in the air above the marine boundary layer. The researchers conducted observations of nitrogen and oxygen isotopes in nitrate particles across the Yellow Sea and Bohai Sea in Eastern China. They found that nitrate concentrations and isotopic ratios showed a clear gradient from north to south. By analyzing the trajectory of air masses, they determined that high nitrate concentrations in the northern sea area were influenced by emissions from the nearby continent, while lower values in the southern sea area were more related to the ocean. The analysis also revealed that different chemical pathways were responsible for nitrate production in these regions. In the northern seas, nitrate production was primarily driven by the reaction of nitrate radicals with hydrocarbons or dimethyl sulfides, while in the southern seas, the dominant pathway involved the reaction of nitrogen dioxide with hydroxyl radicals. The study further showed that nitrate in the northern seas mainly originated from nitrogen oxides emitted by continental sources such as coal combustion and biomass burning, whereas closer to the southern seas, a larger proportion of nitrogen oxides were generated within the marine environment. Key Points: Continental outflow significantly affects the sources and formation mechanisms of atmospheric nitrate in nearshore marine areasAs continental outflow diminishes, local chemistry and marine‐generated NOx become pivotal in producing atmospheric NO3− in the open ocean. In polluted marine boundary layers, NO3 radical‐related chemistry may play a significant role in the formation of nitrate [ABSTRACT FROM AUTHOR]

Oxygen isotope anomaly of nitrate aerosol (∆17O-NO3−) contributes to understanding the atmospheric nitrogen chemistry in the polar oceans. Here, ∆17O-NO3− of the aerosol samples was analyzed based on a cruise from East Asia to the Arctic Ocean to explore the nitrate formation mechanisms. ∆17O-NO3− decreased with the increase of latitude, especially when after entering the Arctic Circle. ∆17O-NO3− (e.g., 11.5‰–21.2‰) was extremely low while crossing the sea ice-covered Arctic Ocean. This is most likely influenced by the combined enhancement of hydroxyl (OH) and peroxy (HO2 + RO2) radicals derived by sea ice under permanent sunlight period. In addition, the obvious increase in the ∆17O-NO3− of return trip with shortened daytime indicated the advantage of nocturnal pathways (NO3 related) with the higher ∆17O endmembers. The mutation of ∆17O-NO3− can reflect the change of NOx conversion pathways to nitrate, and it can be more sensitive to the change of radical chemistry related to atmospheric oxidation. [ABSTRACT FROM AUTHOR]

Inorganic nitrate (NO3−) is a crucial component of fine particulate matter (PM2.5) in haze events in China. Understanding the formation mechanisms of nitrate and the sources of NOx was critical to control the air pollution. In this study, measurements of multiple isotope compositions of nitrate (δ18O‐NO3−, δ17O‐NO3−, and δ15N‐NO3−) in PM2.5 were conducted in Hangzhou from 9 October 2015 to 24 August 2016. Our results showed that oxygen anomaly of nitrate (Δ17O‐NO3−: 20.0‰–37.9‰) and nitrogen isotope of nitrate (δ15N‐NO3−: −2.9‰ to 18.1‰) values were higher in winter and lower in summer. Based on Δ17O‐NO3− observation and a Bayesian model, NO3 radical chemistry was found to dominate the nitrate formation in winter, while photochemical reaction (NO2 + OH) was the main pathway in summer. After considering the nitrogen isotopic fractionation in the NOx(g)‐NO3−(p) conversion, the average contributions of coal combustion, vehicle exhausts, biomass burning, and soil emission were 50% ± 9%, 19% ± 12%, 26% ± 15%, and 5% ± 4%, respectively, to nitrate aerosols during the whole sampling period. Coal combustion was the most important nitrate source in Hangzhou, especially in winter (∼56%). The contribution of soil emission increased significantly in summer due to active soil microbial processes under high temperature environment. Plain Language Summary: Inorganic nitrate is a crucial component of fine particulate matter in haze events in China. Understanding the formation mechanisms and sources of nitrate was critical to control the air pollution. In this study, measurements of multiple isotope compositions of nitrate showed that oxygen anomaly and nitrogen isotope of nitrate are distinct in winter and summer. Then, nitrate radical chemistry was found to dominate the nitrate formation in winter, while photochemical reaction (nitrogen dioxide with hydroxyl radical) was the main pathway in summer. After considering the nitrogen isotopic fractionation in the conversion from nitrogen oxides to nitrate particle, coal combustion was the most important nitrate source in Hangzhou, especially in winter (56%) and the contribution of soil emission increased significantly in summer under high temperature environment. Key Points: NO3 radical chemistry was dominant in nitrate production in the polluted atmosphere in HangzhouThe isotopic fractionation effect in the NOx(g)‐NO3−(p) conversion showed a greater impact on the source apportionment of nitrate aerosolsCoal combustion was the main source of nitrate aerosols in Hangzhou [ABSTRACT FROM AUTHOR]

Excessive reactive oxygen species (ROS) in the human body is an important factor leading to diseases. Therefore, research on the content of reactive oxygen species in atmospheric particles is necessary. In recent years, the online detection technology of ROS has been developed. However, there are few technical studies on online detection of ROS based on the dithiothreitol (DTT) method. Here, to modify the instrument, a DTT experimental module is added that is protected from light and filled with nitrogen at the end based on the Monitor for AeRosols and Gases in ambient Air (MARGA). The experimental study found that the detection limit of the modified instrument is 0.024 nmol min -1. The DTT consumption rate of blank sample (ultrapure water) is reduced by 44 %, which eliminates the influence of outside air and light in the experiment. And the accuracy of the online instrument is determined by comparing the online and offline levels of the samples, which yielded good consistency (slope 0.97, R2=0.95). It shows that the performance of the instrument is indeed optimized, the instrument is stable, and the characterization of ROS is accurate. The instrument not only realizes online detection conveniently and quickly, but also achieves the hour-by-hour detection of ROS based on the DTT method. Meanwhile, reactive oxygen and inorganic ions in atmospheric particles are quantified using the online technique in the northern suburbs of Nanjing. It is found that the content of ROS during the day is higher than that at night, especially after it rains; ROS peaks appear in the two time periods of 08:00–10:00 and 16:00–18:00 (China Standard Time, UTC + 8:00; expressed here in local time – LT). In addition, examination of the online ROS, water-soluble ion (SO42- , NO3- , NH4+ , Na+ , Ca2+ , K+), BC, and polluting gas (SO2 , CO, O3 , NO, NOx) measurements revealed that photo-oxidation and secondary formation processes could be important sources of aerosol ROS. This breakthrough enables the quantitative assessment of atmospheric particulate matter ROS at the diurnal scale, providing an effective tool to study sources and environmental impacts of ROS. [ABSTRACT FROM AUTHOR]

Inorganic nitrate production is critical in atmospheric chemistry that reflects the oxidation capacity and the acidity of the atmosphere. Here we use the oxygen anomaly of nitrate (Δ17O( NO 3 − )) in high-time-resolved (3 h) aerosols to explore the chemical mechanisms of nitrate evolution in fine particles during the winter in Nanjing, a megacity of China. The continuous Δ17O( NO 3 − ) observation suggested the dominance of nocturnal chemistry (NO3 + HC/H2O and N2O5 + H2O/Cl−) in nitrate formation in the wintertime. Significant diurnal variations of nitrate formation pathways were found. The contribution of nocturnal chemistry increased at night and peaked (72%) at midnight. Particularly, nocturnal pathways became more important for the formation of nitrate in the process of air pollution aggravation. In contrast, the contribution of daytime chemistry (NO2 + OH/H2O) increased with the sunrise and showed a highest fraction (48%) around noon. The hydrolysis of N2O5 on particle surfaces played an important role in the daytime nitrate production on haze days. In addition, the reaction of NO2 with OH radicals was found to dominate the nitrate production after nitrate chemistry was reset by the precipitation events. These results suggest the importance of high-time-resolved observations of Δ17O( NO 3 − ) for exploring dynamic variations in reactive nitrogen chemistry. [ABSTRACT FROM AUTHOR]

Oxalate is the product of the precursors that can eventually be oxidized into oxalate by atmospheric oxidants (O3, etc.) and then redistributed to the particle phase, which has an impact on acid rain, and even the climate. However, we are still unclear about the influence of typical atmospheric oxidants in different phases with different RH and pH on oxalates. Here, we analyzed the effects of typical oxidants at RH ≤ 30%, 30% < RH ≤ 80% of the atmosphere on oxalates in atmospheric particulates based on high‐resolution online observation in Nanjing: the chemical processes of O3, OX (=O3 + NO2), and Cl− in different RH all have an important influence on the oxalate level, especially at 30% < RH ≤ 80% with high humidity have greater influence. NO2 only affects the particulate oxalate at RH ≤ 30%; HONO shows a greater effect at RH ≤ 30%, and 30% < RH ≤ 80% in winter and summer, the atmospheric oxidants that dust participates in have little effect. At the same time, we also found the difference between the influence of pH on atmospheric oxalate in winter and summer at RH > 80%, among which high pH is beneficial to the formation of oxalate in summer, while in winter has a greater influence on oxalate at RH ≤ 30%. These results help us to systematically understand the influence and distribution of oxalate in the atmosphere by RH, pH, and typical atmospheric oxidants. Key Points: O3, OX, and Cl− at different humidity ranges in winter and summer have a great influence on atmospheric oxalateDust in winter and summer have similar effects on atmospheric oxalate levelsHigh pH is beneficial to the formation of oxalate at RH > 80% in summer and at RH ≤ 30% in winter [ABSTRACT FROM AUTHOR]

To understand the influences of continental emissions on marine aerosols from East Asia, the total suspended particle (TSP) samples were collected from the Yellow Sea (YS) and Bohai Sea (BS) of China through a cruise campaign during the spring of 2018. >100 individual organic compounds were identified and determined in the samples, and they were classified into 6 major groups according to the functionality and sources. The mass concentrations of total quantified organic compounds in BS (307.6 ± 268.3 ng m−3) was approximately 3 times those of YS (111.0 ± 97.3 ng m−3). Organic compounds from biomass burning (23.2 ± 34.2 ng m−3), marine/microbial source (23.1 ± 6.2 ng m−3) and fossil fuel combustion (21.4 ± 11.3 ng m−3) were the most abundant in the YS samples, whereas primary biological origins (90.0 ± 107.1 ng m−3), biomass burning (52.1 ± 39.1 ng m−3) and fossil fuel combustion (41.9 ± 20.1 ng m−3) were the most important organic species in BS marine aerosols. The concentrations of total biogenic secondary organic aerosol (BSOA) tracers including six isoprene SOA (SOA I), three monoterpene SOA (SOA M), and one β -caryophyllene SOA (SOA C) were 2.4 ± 1.5 ng m−3 and 7.3 ± 4.4 ng m−3 in the YS and BS samples, respectively. A strong correlation between BSOA tracers and levoglucosan was shown in the marine aerosol samples, indicating that biomass burning emissions could also promote BSOA formations. The spatial distribution of chemical and source characteristics suggests a relatively large impacts of continental emissions to the BS aerosols. Based on the tracer-based method, the biomass burning (YS: 4.9 ± 6.8%; BS: 8.8 ± 8.0%) was the largest contributor to OC, followed by primary biogenic OC (YS: 0.59 ± 0.44%; BS: 2.9 ± 3.0%) and biogenic secondary OC (YS: 0.45 ± 0.23%; BS: 1.0 ± 0.59%). This study suggests important contributions of biomass burning emissions to organic aerosols in the YS and BS marine atmosphere, although marine source, fossil fuel combustion and secondary formation was also substantial. [Display omitted] • Chemical and source characteristics of marine organic aerosols over the Bohai Sea and Yellow Sea were studied. • Biomass burning is a major contributor of marine organic aerosols over the Bohai Sea and Yellow Sea. • Biogenic primary emission contribution to organic carbon is higher than biogenic-derived secondary formation. • The Bohai Sea is more receptive to the input of continental emissions than the Yellow Sea. [ABSTRACT FROM AUTHOR]

The North China Plain (NCP) is becoming one of the most polluted areas characterized by a high frequency of haze pollution. However, the spatial and temporal evolutions of aerosol chemical compositions in such a highly polluted region are not well understood due to the lack of a long-term and comprehensive observation-based network. China's National Aerosol Composition Monitoring Network (NACMON) has conducted comprehensive offline and online measurements of compositions and optical properties of airborne aerosols in order to systematically investigate the formation process, source apportionments of haze, and interactions between haze pollution and climate change. The objective of the observations is to provide information for policy makers to make strategies for the alleviation of haze occurrence. In this paper, we present instrumentations and methodologies as well as the preliminary results of the offline observations in NACMON stations over the NCP region. The implications and future perspectives of the network are also summarized. Benefiting from simultaneous observations from this network, we found that secondary aerosols were the dominant component in haze pollution. High anthropogenic emissions, low wind speed, and high relative humidity (RH) facilitated gas-to-particle transformation and resulted in high PM2.5 formation (PM2.5 is particulate matter that is smaller than 2.5 μm in diameter). Sulfate-dominant or nitrate-dominant aerosols during the haze period were driven by ambient RH. Moreover, the contributions of coal combustion and biomass burning to PM2.5 revealed downward trends, whereas secondary aerosols showed upward trends over the last decade. Thus, we highlighted that strict control of anthropogenic emissions of precursor gases, such as NOx, NH3, and volatile organic compounds (VOCs), will be an important way to decrease PM2.5 pollution in the NCP region. [ABSTRACT FROM AUTHOR]

Water-soluble organic carbon (WSOC) is a significant fraction of organic carbon (OC) in atmospheric aerosols. WSOC is of great interest due to its significant effects on atmospheric chemistry, the Earth's climate and human health. The stable carbon isotope (δ13C) can be used to track the potential sources and investigate atmospheric processes of organic aerosols. However, the previous methods measuring the δ13C values of WSOC in ambient aerosols require a large amount of carbon content, are time-consuming and require labor-intensive preprocessing. In this study, a method of simultaneously measuring the mass concentration and the δ13C values of WSOC from aerosol samples is established by coupling the GasBench II preparation device with isotopic ratio mass spectrometry. The precision and accuracy of isotope determination is better than 0.17 ‰ and 0.5 ‰, respectively, for samples containing WSOC amounts larger than 5 µg. This method is then applied for the aerosol samples collected every 3 h during a severe wintertime haze period in Nanjing, eastern China. The WSOC values vary between 3 and 32 µg m -3 , whereas δ13C-WSOC ranges from -26.24 ‰ to -23.35 ‰. Three different episodes (Episode 1, Episode 2 and Episode 3) are identified in the sampling period, showing a different tendency of δ13C-WSOC with the accumulation process of WSOC aerosols. The increases in both the WSOC mass concentrations and the δ13C-WSOC values in Episode 1 indicate that WSOC is subject to a substantial photochemical aging during the air mass transport. In Episode 2, the decline of the δ13C-WSOC is accompanied by the increase in the WSOC mass concentrations, which is associated with regional-transported biomass burning emissions. In Episode 3, heavier isotope (13C) is exclusively enriched in total carbon (TC) in comparison to WSOC aerosols. This suggests that the non-WSOC fraction in total carbon may contain 13C -enriched components such as dust carbonate, which is supported by the enhanced Ca2+ concentrations and air mass trajectory analysis. The present study provides a novel method to determine the stable carbon isotope composition of WSOC, and it offers a great potential to better understand the source emission, the atmospheric aging and the secondary production of water-soluble organic aerosols. [ABSTRACT FROM AUTHOR]

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–NO 3 - and δ18O–NO 3 - characteristics of PM 2.5 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 (εN) during the conversion of atmospheric NO X (δ15N-NO X) to nitrate (δ15N–NO 3 -) was discussed on the basis of the estimated contributions of the gas phase oxidation pathway of OH radical (·OH) (γ OH) and the heterogeneous hydrolysis pathway of N 2 O 5 (γ N2O5) to nitrate formation. Besides, the contribution of biological soil, coal combustion, biomass burning and motor vehicles to NO X 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 NO X 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 NO X emissions in the Northeast, showing a contribution of 5.2%–35.8%. It is worth noting that in urban site (a) where the tropospheric O 3 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 O 3. 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 (N 2 O 5 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%). [Display omitted] • Nitrate sources and formation of PM 2.5 at different types of sites in Northeast China were determined by N and O isotopes. • Coal combustion dominated winter nitrate production in Northeast China, especially in rural area. • The difference in the formation of nitrate in urban and non-urban areas may be due to the different O 3 concentration. • The haze period was conducive to the heterogeneous reaction of nitrate. [ABSTRACT FROM AUTHOR]

One-hour resolution observations of stable carbon isotopes in both gaseous water-soluble organic carbon (WSOCg) and particulate water-soluble organic carbon (WSOCp) were conducted at a city site in the Yangtze River Delta. WSOCg exhibited significantly higher concentrations and lower 13C compared to WSOCp. The presence of radiation emerged as a crucial factor influencing the gas-particle partitioning mechanism of WSOC. There appeared to be distinct formation processes for WSOCp and WSOCg during nighttime, except on hazy days with elevated particulate matter concentrations. Gas-particle partitioning of WSOC may become inactive in environments with high temperatures and ozone concentrations, while it may become active in environments characterized by high relative humidity (RH) and elevated WSOCg concentrations. When addressing WSOC pollution, it's essential to focus not only on its sources but also on the suitable environmental conditions for gas-particle partitioning. Active gas-particle partitioning of WSOC may coincide with the formation of secondary inorganic ions (NH 4 +, NO 3 − and SO 4 2−). Thus, in targeting WSOC sources, it's imperative to implement coordinated strategies to control the sources of secondary inorganic ions. • Photochemical production is a critical mechanism of WSOC gas-particle partitioning during the wintertime. • δ13C–WSOC is influenced by both WSOC source compositions, meteorological conditions and gaseous pollutants concentrations. • Secondary inorganic ions are formed synergistically during gas-particle partitioning of WSOC. [ABSTRACT FROM AUTHOR]

Air quality in China is tending to improve, especially in urban areas. Nevertheless, rural areas and underdeveloped cities in northern China are still suffering from severe air pollution in winter due to large usage of coal and unfavorable meteorological conditions. In this study, size-segregated aerosol samples were collected from a typical coal-combustion rural site in Linfen, China during an extreme air pollution episode in winter 2017. The polycyclic aromatic hydrocarbons (PAHs), n -alkanes, hopanes and steranes were identified to better understand the emission sources of the organic compounds and the health effects of the PAHs in the ambient air here. The PAHs showed a bimodal mode with the major peak in the Aitken mode (<0.4 μm) and the minor one in the size range of 0.7–2.1 μm. Daily PAHs level ranged from 0.5–1.6 μg m−3 (average: 1.1 ± 0.3 μg m−3) which was 1–2 orders of magnitude higher than other major cities in China. The plots of log (PAH/PM)-log(Dp) showed the slope near −1 for four-, five- and six-ring PAHs, indicating both the adsorption and absorption mechanisms controlled the size distribution. The deposition efficiency displayed a bimodal mode in alveolar region (AR), and the major peak was within the Aitken mode. The total deposition flux (DF) in AR region was 92.7 ng h−1, and the DF based lifetime cancer risk (LCR) was about 2.7 × 10−4 for adults and 2.0 × 10−4 for children which were 2 orders of magnitude higher than the acceptable level of 10−6 proposed by United States Environmental Protection Agency (US EPA). In summary, the residential coal combustion was the most important source of PAHs, especially they emitted a large amount of PAHs in Aitken mode which led to the terrible air quality and high level of health risk. Therefore, the environmental protection measures should be tightened in such rural areas of north China. • Size-segregated samples were collected to study the PM 10 -bond PAHs in a typical coal combustion rural site in north China. • More than 60% of the PM 10 -bond PAHs were concentrated on PM 0.4 and the residential coal combustion was the primary source. • Hopanes and steranes, the molecular biomarkers of coal combustion, were identified in this study. • The Lifetime cancer risk was about two orders of magnitude higher than the guideline of 10−6. [ABSTRACT FROM AUTHOR]

In recent years, there are still huge amounts of NOx emissions in the Northeast, and this inevitably increases the concentration of aerosol nitrate (NO 3 −), which plays an important role in atmospheric pollution. Because of the mixed sources of atmospheric NO 3 −, 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 NO X have different ranges of δ15N values, δ15N is considered to be a useful tool for identifying the source of aerosol NO 3 −. But isotope fractionation occurs during the conversion of NO X to NO 3 −, and δ18O can be used to estimate its isotope fractionation value. In this study, daily PM 2.5 samples were collected in four seasons from Northeast China, and their water-soluble ionic components (WSIs), δ15N–NO 3 - and δ18O–NO 3 - were analyzed. The isotope fractionation value of δ15N in which NO X was converted to NO 3 − was estimated and the contribution of different sources was quantified in combination with the Bayesian model. The results showed that NO 3 − 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 NO 3 − in Northeast China. Image 1 • Coal combustion and biomass burning dominated the production of nitrate in Northeast China. • Nitrate was formed mainly through the OH radical pathway in Northeast China. • In winter, coal combustion dominated the production of NO X , while in other seasons biomass burning dominated. • The dominant source of nitrate during heating period and non-heating period were coal combustion and biomass burning, respectively. [ABSTRACT FROM AUTHOR]

We examined the characteristics and source apportionment of organic aerosols in ambient PM 2.5 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. 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. Image 1 • The chemical and source characteristics of organic aerosols in Northeast China was studied. • 90 individual species were quantified with biomass burning tracers as most abundant compounds. • NOx influence SOA formation from isoprene. • Fossil combustion (42.4%) and biomass burning (33.6%) were most important contributors of OA. • Biogenic aerosol is a non-negligible contributor. [ABSTRACT FROM AUTHOR]

Nitrate is the major component of fine particle matter in recent years, and fog deposition is an important sink form of atmospheric nitrate aerosol. However, evidence shows that high relative humidity, and stable atmosphere condition may lead to the rapid increase of secondary aerosols, including nitrate. Therefore, whether fog event is a sink or a source of nitrate aerosol is still an open question. Simultaneous observations of concentration and isotopes of nitrate both in PM 2.5 and fog water during fog event were conducted during a heavy fog event happened in winter of 2018 in Nanjing, a megacity sited in the Yangzi River Delta, China. Based on nine 12-h time resolution fog water samples and eleven 24-h time resolution PM 2.5 samples, it was found that NO 3 − concentration in PM 2.5 increased during the fog event (from 10.4 ± 8.6 μg m−3 to 21.2 ± 11.0 μg m−3). Compared with Δ17O–NO 3 - in PM 2.5 before (28.4 ± 3.7‰) and after the fog event (28.6 ± 1.3‰), Δ17O–NO 3 - in PM 2.5 during the fog event was higher (31.6 ± 1.2‰) and Δ17O–NO 3 - in fog water was lower (24.3 ± 1.2‰). The increased NO 3 − in PM 2.5 during the fog event had a different formation pathway compared with NO 3 − in PM 2.5 when there is no fog, and NO 3 − in fog water had another formation pathway as well. Explosive growth of NO 3 − in PM 2.5 may come from active NO 3 + HC reaction, along with happen of fog event through the reaction of NO 2 with ·OH or H 2 O and hydrolysis of N 2 O 5. As the fog event finished, the fog water possibly mainly settled NO 3 − newly generated during the fog event. It seems the fog event may be a source rather than a sink of atmospheric nitrate aerosols in this case. [Display omitted] • Nitrate is the main ion in fog water in urban area, mainly come from reaction of NO 2 with ·OH/H 2 O and hydrolysis of N 2 O 5. • Plenty of nitrate particles generated by reaction of NO 3 with HC/H 2 O during the fog event, mainly came from coal burning. • Fog water mainly settled nitrate particles newly generated during the fog event rather than that before the fog event. [ABSTRACT FROM AUTHOR]

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 PM 2.5. Abrupt enhancements of nitrogen-containing aerosols (e.g., NO 3 − and NH 4 +) were found in the winter, and nitrate became as a dominant contributor in high pollution days (e.g., PM 2.5 > 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 PM 2.5 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 NH 3 from combustion-related emissions (49%), NH 3 derived from animal wastes (6%), NH 3 from urban volatilization (3%), NO x derived from coal combustion (33%), NO x from biomass burning (5%) and NO x from vehicles (3%). Our results demonstrated that ambient NO x was dominated by coal combustion. Since NO x and NH 3 are important precursors for ammonium nitrate aerosols, controlling of combustion related NO x and NH 3 emissions might be an important way to reduce PM 2.5 levels in this region. Image 1 • Nitrate was the dominant contributor of water soluble inorganic ions in high PM 2.5 pollution days. • The optimized Bayesian isotope mixing model (SIAR) improved accuracy and reduced the overall uncertainties, indicating modified SIAR improve accuracy in estimations of TN sources. • Combustion related NO x and NH 3 emissions were the most predominant sources to nitrogen-containing aerosols (TN). [ABSTRACT FROM AUTHOR]

[Display omitted] • 14C-based source apportionment of carbonaceous aerosols in Chiang Mai is reported. • Biomass burning is the dominant contributor to fine aerosols. • The fossil-derived SOC is more tended to be produced in low biomass burning season. Biomass burning (BB) is an important contributor to the air pollution in Southeast Asia (SEA), but the emission sources remain great uncertainty. In this study, PM 2.5 samples were collected from an urban (Chiang Mai University, CMU) and a rural (Nong Tao village, NT) site in Chiang Mai, Thailand from February to April (high BB season, HBB) and from June to September (low BB season, LBB) in 2018. Source apportionment of carbonaceous aerosols was carried out by Latin Hypercube Sampling (LHS) method incorporating the radiocarbon (14C) and organic markers (e.g., dehydrated sugars, aromatic acids, etc.). Thereby, carbonaceous aerosols were divided into the fossil-derived elemental carbon (EC f), BB-derived EC (EC bb), fossil-derived primary and secondary organic carbon (POC f , SOC f), BB-derived OC (OC bb) and the remaining OC (OC nf, other). The fractions of EC bb generally prevailed over EC f throughout the year. OC bb was the dominant contributor to total carbon with a clear seasonal trend (65.5 ± 5.8 % at CMU and 79.9 ± 7.6 % at NT in HBB, and 39.1 ± 7.9 % and 42.8 ± 4.6 % in LBB). The distribution of POC f showed a spatial difference with a higher contribution at CMU, while SOC f displayed a temporal variation with a greater fraction in LBB. OC nf, other was originated from biogenic secondary aerosols, cooking emissions and bioaerosols as resolved by the principal component analysis with multiple liner regression model. The OC nf, other contributed within a narrow range of 6.6 %-14.4 %, despite 34.9 ± 7.9 % at NT in LBB. Our results highlight the dominance of BB-derived fractions in carbonaceous aerosols in HBB, and call the attention to the higher production of SOC in LBB. [ABSTRACT FROM AUTHOR]

Secondary inorganic aerosols, including sulfate, nitrate, and ammonium (SNA), are the predominant components of fine particles (PM 2.5). Reasonable representations of SNA formation in numerical models can largely improve the predictions of PM 2.5 concentrations and effectively help implement emission control strategies. Despite the Atmospheric Pollution Prevention and Control Action Plan has been implemented since 2013, PM 2.5 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 PM 2.5 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 PM 2.5 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 SO 2 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 SO 2 to sulfate is significantly underestimated in the model. Tripling the gas-phase oxidation rate of SO 2 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 SO 2 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. • SO 4 underestimates by 71% (84%), while NO 3 overestimates by 45% (67%) in Apr. (Jan.). NH 4 is consistent with the observation. • Underestimated SO 4 is accompanied by overestimated SO 2 by 27% (74%) in Apr. (Jan.), indicating SO 2 oxidation rate may be low. • Compared to the reference run, tripling SO 2 gas-phase oxidation rate only increases SO 4 by 67% (72%) in Apr. (Jan.). • Incorporating SO 2 heterogeneous reaction in aerosol water can increase SO 4 y 84% (196%) in Apr. (Jan.). • Incorporating SO 2 heterogeneous reaction can also better reproduce the observed diurnal variation. [ABSTRACT FROM AUTHOR]