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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]

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]

Environmentally persistent free radicals (EPFRs) are a new type of substance with potential health risks. EPFRs are widely present in atmospheric particulates, but there is a limited understanding of the size-resolved health risks of these radicals. This study reports the exposure risks and source of EPFRs in atmospheric particulate matter (PM) of different particle sizes (<10 µm) in Linfen, a typical coal-burning city in China. The type of EPFRs in fine particles (< 2.1 µm) is different from that in coarse particles (2.1–10 µm) in both winter and summer. However, the EPFR concentration is higher in coarse particles than in fine particles in summer, and the opposite trend is found in winter. In both seasons, combustion sources are the main sources of EPFRs, with coal combustion as the major contributor in winter, while other fuels are the major source in summer. Dust contributes part of the EPFRs, and it is mainly present in coarse particles in winter and the opposite in summer. The upper respiratory tract was found to be the area with the highest risk of exposure to EPFRs of the studied aerosols, with an exposure equivalent to that of approximately 21 cigarettes per person per day. Alveolar exposure to EPFRs is equivalent to 8 cigarettes per person per day, with combustion sources contributing the most to EPFRs in the alveoli. This study helps us to better understand the potential health risks of atmospheric PM with different particle sizes. [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]

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]

Fine particulate matter samples (PM 2.5) were collected from the three megacities of the Yangtze River Delta (i.e., Shanghai, Hangzhou, and Nanjing) during November 11 to December 6, 2016. Organic carbon (OC), elemental carbon (EC), and four types of non-polar organic compounds such as polycyclic aromatic hydrocarbons (PAHs), n -alkanes, hopanes and steranes were analyzed in the samples. The average PM 2.5 mass concentrations were 47.0, 64.2 and 45.5 μg m−3 in Shanghai, Hangzhou and Nanjing, respectively. OC and EC concentrations were 4.47 and 0.78 μg m−3, 15.38 and 2.97 μg m−3, 10.35 and 2.06 μg m−3, respectively. n -Alkanes accounted for the largest abundance of the identified non-polar organic compounds, followed by PAHs, hopanes and steranes. The positive matrix factorization (PMF) analysis demonstrated that vehicular emissions, coal burning and industrial emissions were the most important sources. Vehicle exhaust was the major source of emissions in Shanghai (61.0%) and Hangzhou (45.3%), whereas coal combustion emissions was dominant (48.8%) in Nanjing. In addition, the estimated lifetime cancer risk (ILCR) values exposed to PAHs for adults (6.54 × 10−5) and children (7.32 × 10−6) suggested that PAHs levels in this region pose potential health risks. Combining the health risk model with PMF further concluded that vehicular emissions (49.0%) and coal burning (35.7%) were the two major sources that contribute to the ILCR values in these three cities. • Characteristics and source apportionment of NPOCs from three megacities in the YRD were studied. • NPOCs with unique sources were used to track the source of the aerosols. • Vehicular emissions and coal burning were most important contributors of NPOCs. • Polycyclic aromatic hydrocarbons pose a greater health risk to adult than children. • Combining the health risk model and PMF to reveal the contribution of each source to health risk. [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]

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]

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. Image 1 • Quantification of PAHs in highly size resolved particles from 0.01 μm to 10 μm. • PAHs from wood increase with temperature increasing while it is opposite from coal. • PAHs emissions have different characteristics during each combustion processes. • The formation pathway of PAHs during wood and coal combustions are different. [ABSTRACT FROM AUTHOR]