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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]

Carbonaceous aerosols have great influence on the air quality, human health and climate change. Except for organic carbon (OC) and elemental carbon (EC), brown carbon (BrC) mainly originates from biomass burning as a group of OC, with strong absorption from the visible to near-ultraviolet wavelengths, and makes a considerable contribution to global warming. Large numbers of studies have reported long-term observation of OC and EC concentrations throughout the world, but studies of BrC based on long-term observations are rather limited. In this study, we established a two-wavelength method (658 and 405 nm) applied in the Sunset thermal–optical carbon analyzer. Based on a 1-year observation, we firstly investigated the characteristics, meteorological impact and transport process of OC and EC. Since BrC absorbs light at 405 nm more effectively than 658 nm, we defined the enhanced concentrations (dEC = EC 405nm - EC 658nm) and gave the possibility of providing an indicator of BrC. The receptor model and MODIS fire information were used to identify the presence of BrC aerosols. Our results showed that the carbonaceous aerosol concentrations were the highest in winter and lowest in summer. Traffic emission was an important source of carbonaceous aerosols in Nanjing. Receptor model results showed that strong local emissions were found for OC and EC; however, dEC was significantly affected by regional or long-range transport. The dEC/OC and OC/EC ratios showed similar diurnal patterns, and the dEC/OC increased when the OC/EC ratios increased, indicating strong secondary sources or biomass burning contributions to dEC. A total of two biomass burning events both in summer and winter were analyzed, and the results showed that the dEC concentrations were obviously higher on biomass burning days; however, no similar levels of the OC and EC concentrations were found both in biomass burning days and normal days in summer, suggesting that biomass burning emissions made a great contribution to dEC, and the sources of OC and EC were more complicated. Large number of open fire counts from the northwestern and southwestern areas of the study site were observed in winter and significantly contributed to OC, EC and dEC. In addition, the nearby Yangtze River Delta area was one of the main potential source areas of dEC, suggesting that anthropogenic emissions could also be important sources of dEC. The results proved that dEC can be an indicator of BrC on biomass burning days. Our modified two-wavelength instrument provided more information than the traditional single-wavelength thermal–optical carbon analyzer and gave a new idea about the measurement of BrC; the application of dEC data needs to be further investigated. [ABSTRACT FROM AUTHOR]

Ammonia (NH3) is an important agent involved in atmospheric chemistry and nitrogen cycling. Current estimates of NH3 emissions from biomass burning (BB) differ by more than a factor of 2, impeding a reliable assessment of their environmental consequences. Combining high-resolution satellite observations of NH3 columns with network measurements of the concentration and stable nitrogen isotope composition (δ15N) of NH3 , we present coherent estimates of the amount of NH3 derived from BB in the heartland of Southeast Asia, a tropical monsoon environment. Our results reveal a strong variability in atmospheric NH3 levels in time and space across different landscapes. All of the evidence on hand suggests that anthropogenic activities are the most important modulating control with respect to the observed patterns of NH3 distribution in the study area. N-isotope balance considerations revealed that during the intensive fire period, the atmospheric input from BB accounts for no more than 21±5 % (1σ) of the ambient NH3 , even at the rural sites and in the proximity of burning areas. Our N-isotope-based assessment of the variation in the relative contribution of BB-derived NH3 is further validated independently through the measurements of particulate K+ , a chemical tracer of BB. Our findings underscore that BB-induced NH3 emissions in tropical monsoon environments can be much lower than previously anticipated, with important implications for future modeling studies to better constrain the climate and air quality effects of wildfires. [ABSTRACT FROM AUTHOR]

Carbonaceous aerosols have great influence on the air quality, human health and climate change. Except for organic carbon (OC) and elemental carbon (EC), brown carbon (BrC), mainly originates from biomass burning, as a group of OC with strong absorption from the visible to near ultraviolet wavelengths, makes a considerable contribution to global warming. Large amounts of studies have reported long-term observation of OC and EC concentrations throughout the word, but studies of BrC based on long-term observations are rather limited. In this study, we established two-wavelength method (658 nm and 405 nm) applied in the Sunset thermo/optical carbon analyzer. Based on one-year observation, we firstly investigated the characteristics, meteorological impact and transport process of OC and EC. Due to BrC absorbs light at 405 nm more effectively than 658 nm, we defined the enhanced concentrations (dEC =EC405 nm—EC658 nm) and gave the possibility to provide an indicator of BrC. The receptor model and MODIS fire information were used to identify the presence of BrC aerosols. Our results showed that the carbonaceous aerosols concentrations were highest in winter and lowest in summer. Traffic emission was an important source of carbonaceous aerosols in Nanjing. Receptor model results showed that strong local emissions were found in OC and EC aerosols, however dEC aerosols were significantly affected by regional or long-range transport. The dEC/OC and OC/EC ratios showed similar diurnal patterns and the dEC/OC increased when the OC/EC ratios increased, indicating strong secondary sources or biomass burning contributions to dEC. Two biomass burning events both in summer and winter were analyzed and the results showed that the dEC concentrations were obvious higher in biomass burning days, however, no similar levels of the OC and EC concentrations were found both in biomass burning days and normal days in summer, suggesting that biomass burning emission made a great contribution to dEC and the sources of OC and EC were more complicated. Large number of open fire counts from the northwest and southwest areas of the study site were monitored in winter, significantly contributed to OC, EC and dEC. In addition, the near-by YRD area was one of the main potential source areas of dEC, suggesting that anthropogenic emissions could also be important sources of dEC. The results proved that dEC can be an indicator of BrC in biomass burning days. Our modified two-wavelength instrument provided more information than traditional single-wavelength thermo/optical carbon analyzer and gave a new idea about the measurement of BrC, the application of dEC data need to be further investigated. [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]

Predicting tropospheric cloud formation and subsequent nutrient deposition relies on understanding the sources and processes affecting aerosol constituents of the atmosphere that are preserved in cloud water. However, this challenge is difficult to address quantitatively based on the sole use of bulk chemical properties. Nitrogenous aerosols, mainly ammonium (NH4+) and nitrate (NO3-), play a particularly important role in tropospheric cloud formation. While dry and wet (mainly rainfall) deposition of NH4+ and NO3- are regularly assessed, cloud water deposition is often underappreciated. Here we collected cloud water samples at the summit of Mt. Tai (1545 m above sea level) in eastern China during a long-lasting biomass burning (BB) event and simultaneously measured for the first time the isotopic compositions (mean ±1σ) of cloud water nitrogen species (δ15N-NH4+ = - 6.53 ‰ ± 4.96 ‰, δ15N-NO3- = - 2.35 ‰ ± 2.00 ‰, δ18O-NO3- = 57.80 ‰ ± 4.23 ‰), allowing insights into their sources and potential transformation mechanism within the clouds. Large contributions of BB to the cloud water NH4+ (32.9 % ± 4.6 %) and NO3- (28.2 % ± 2.7 %) inventories were confirmed through a Bayesian isotopic mixing model, coupled with our newly developed computational quantum chemistry module. Despite an overall reduction in total anthropogenic NOx emission due to effective emission control actions and stricter emission standards for vehicles, the observed cloud δ15N-NO3- values suggest that NOx emissions from transportation may have exceeded emissions from coal combustion. δ18O-NO3- values imply that the reaction of OH with NO2 is the dominant pathway of NO3- formation (57 % ± 11 %), yet the contribution of heterogeneous hydrolysis of dinitrogen pentoxide was almost as important (43 % ± 11 %). Although the limited sample set used here results in a relatively large uncertainty with regards to the origin of cloud-associated nitrogen deposition, the high concentrations of inorganic nitrogen imply that clouds represent an important source of nitrogen, especially for nitrogen-limited ecosystems in remote areas. Further simultaneous and long-term sampling of aerosol, rainfall, and cloud water is vital for understanding the anthropogenic influence on nitrogen deposition in the study region. [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]

Biomass burning can significantly impact the chemical and optical properties of carbonaceous aerosols. Here, the biomass burning impacts were studied during wintertime in a megacity of Nanjing, eastern China. The high abundance of biomass burning tracers such as levoglucosan (lev), mannosan (man), galactosan (gal) and non-sea-salt potassium (nss- K+) was found during the studied period with the concentration ranges of 22.4–1476 ng m -3 , 2.1–56.2 ng m -3 , 1.4–32.2 ng m -3 and 0.2–3.8 µ g m -3 , respectively. The significant contribution of biomass burning to water-soluble organic carbon (WSOC; 22.3±9.9 %) and organic carbon (OC; 20.9±9.3 %) was observed in this study. Backward air mass origin analysis, potential emission sensitivity of elemental carbon (EC) and MODIS fire spot information indicated that the elevations of the carbonaceous aerosols were due to the transported biomass-burning aerosols from southeastern China. The characteristic mass ratio maps of lev/man and lev/nss - K+ suggested that the biomass fuels were mainly crop residuals. Furthermore, the strong correlation (p<0.01) between biomass burning tracers (such as lev) and light absorption coefficient (babs) for water-soluble brown carbon (BrC) revealed that biomass burning emissions played a significant role in the light-absorption properties of carbonaceous aerosols. The solar energy absorption due to water-soluble brown carbon and EC was estimated by a calculation based on measured light-absorbing parameters and a simulation based on a radiative transfer model (RRTMG_SW). The solar energy absorption of water-soluble BrC in short wavelengths (300–400 nm) was 0.8±0.4 (0.2–2.3) W m -2 (figures in parentheses represent the variation range of each parameter) from the calculation and 1.2±0.5 (0.3–1.9) W m -2 from the RRTMG_SW model. The absorption capacity of water-soluble BrC accounted for about 20 %–30 % of the total absorption of EC aerosols. The solar energy absorption of water-soluble BrC due to biomass burning was estimated as 0.2±0.1 (0.0–0.9) W m -2 , considering the biomass burning contribution to carbonaceous aerosols. Potential source contribution function model simulations showed that the solar energy absorption induced by water-soluble BrC and EC aerosols was mostly due to the regionally transported carbonaceous aerosols from source regions such as southeastern China. Our results illustrate the importance of the absorbing water-soluble brown carbon aerosols in trapping additional solar energy in the low-level atmosphere, heating the surface and inhibiting the energy from escaping the atmosphere. [ABSTRACT FROM AUTHOR]

PM 2.5 aerosol samples were collected from the Chinese megacity of Nanjing (32.21 ∘ N, 118.73 ∘ E) during winter and analyzed for a total of 127 compounds from 12 organic compound classes. The most abundant classes of compounds were n -alkanes (mean concentration of 205 ng m -3), followed by fatty acids (76.3 ng m -3), polycyclic aromatic hydrocarbons (PAHs; 64.3 ng m -3), anhydrosugars (56.3 ng m -3), fatty alcohols (40.5 ng m -3) and phthalate esters (15.2 ng m -3), whereas hydroxy-/polyacids (8.33 ng m -3), aromatic acids (7.35 ng m -3), hopanes (4.19 ng m -3), primary sugars and sugar alcohols (4.15 ng m -3), lignin and resin products (2.94 ng m -3), and steranes (2.46 ng m -3) were less abundant. The carbon preference index of n -alkanes (0.83–1.38) indicated that they had a strong fossil fuel combustion origin. Diagnostic concentration ratios of organic tracers suggested that PAHs and hopanes originated mostly from coal burning and traffic emissions, respectively, in the Nanjing urban area. Positive matrix factorization analysis demonstrated that fossil fuel combustion was the major pollution source (28.7 %), followed by emissions from biomass burning (17.1 %), soil dust (14.5 %) and plastic burning (6.83 %) for Nanjing winter aerosols, although the contribution of secondary oxidation products (32.9 %) was the most abundant. Most of the compounds generally showed higher concentrations at nighttime compared with daytime; this was due to the accumulation process associated with inversion layers and the enhancement of emissions from heavy trucks at night. We conclude that fossil fuel combustion largely influences the winter organic aerosols in urban Nanjing. Based on the comparison of this study's results with previous research, we found that pollution levels in organic aerosols have decreased in the urban Nanjing atmosphere over the last decade. [ABSTRACT FROM AUTHOR]

Carbonaceous aerosol (total carbon, TC p) was source apportioned at nine European rural background sites, as part of the European Measurement and Evaluation Programme (EMEP) Intensive Measurement Periods in fall 2008 and winter/spring 2009. Five predefined fractions were apportioned based on ambient measurements: elemental and organic carbon, from combustion of biomass (EC bb and OC bb) and from fossil-fuel (EC ff and OC ff) sources, and remaining non-fossil organic carbon (OC rnf), dominated by natural sources. OC rnf made a larger contribution to TC p than anthropogenic sources (EC bb , OC bb , EC ff , and OC ff) at four out of nine sites in fall, reflecting the vegetative season, whereas anthropogenic sources dominated at all but one site in winter/spring. Biomass burning (OC bb + EC bb) was the major anthropogenic source at the central European sites in fall, whereas fossil-fuel (OC ff + EC ff) sources dominated at the southernmost and the two northernmost sites. Residential wood burning emissions explained 30 %–50 % of TC p at most sites in the first week of sampling in fall, showing that this source can be the dominant one, even outside the heating season. In winter/spring, biomass burning was the major anthropogenic source at all but two sites, reflecting increased residential wood burning emissions in the heating season. Fossil-fuel sources dominated EC at all sites in fall, whereas there was a shift towards biomass burning for the southernmost sites in winter/spring. Model calculations based on base-case emissions (mainly officially reported national emissions) strongly underpredicted observational derived levels of OC bb and EC bb outside Scandinavia. Emissions based on a consistent bottom-up inventory for residential wood burning (and including intermediate volatility compounds, IVOCs) improved model results compared to the base-case emissions, but modeled levels were still substantially underestimated compared to observational derived OC bb and EC bb levels at the southernmost sites. Our study shows that natural sources are a major contributor to carbonaceous aerosol in Europe, even in fall and in winter/spring, and that residential wood burning emissions are equally as large as or larger than that of fossil-fuel sources, depending on season and region. The poorly constrained residential wood burning emissions for large parts of Europe show the obvious need to improve emission inventories, with harmonization of emission factors between countries likely being the most important step to improve model calculations for biomass burning emissions, and European PM 2.5 concentrations in general. [ABSTRACT FROM AUTHOR]

Arsenic (As) has long been recognized as a toxic element of mainly anthropogenic origins, having adverse effects on human health. However, there is insufficient understanding regarding As released into atmosphere from biomass burning (BB). To this end, daily airborne As concentrations in total particulate matter (TSP) were determined at Mount Hehuan (24.16° N, 121.29° E, 3001ma.s.l.), Taiwan from September 2011 to September 2012. During the sampling period, As concentrations varied from 0.02 to 5.9 ngm-3 with a mean value of 0.5±.0 ngm-3. Significantly seasonal variations of As were found over the subtropical free troposphere, and higher As concentrations were observed in the southern (S) and southeastern (SE) Asian BB seasons (from January to May). Principal component analysis (PCA) results showed that BB activities seemed to be a major source of As during the S and SE Asian BB periods, which were very distinct from the major source of coal-fired power plant during the periods between July and December. Based on backward trajectory analyses and WRF-Chem model simulations, we found that the high As concentrations during the BB periods were attributed to the biomass burning activities over S Asia where groundwater, soil and crops are severely contaminated by arsenic. A strong correlation (r = 0:73 p < 0:05) between As and potassium ion (KC, a chemical tracer of BB activities) in S Asian BB events also supported this hypothesis. During the S Asian BB events, the high As = Pb ratios (> 0:2) were also observed, indicating that burning crops contaminated by lead arsenate might be a crucial candidate for high As concentrations at Mount Hehuan. Nevertheless, the net influence of S Asian BB activities on airborne As concentrations has been estimated by comparing the differences of As concentrations on BB and non-BB days. On average, the difference in As concentrations was 1.0 ngm-3, which accounted for 63% of the average As concentration on BB days. Moreover, a ratio of 1As=1CO (~ 0:00001) in the S Asian BB events was obtained. Using this value, arsenic emissions from S Asian BB activities were estimated to be 0.17 tons yr-1 , resulting in high airborne As concentrations over the subtropical free troposphere and impacting As cycles on a regional scale in the S and SE Asian BB seasons. [ABSTRACT FROM AUTHOR]

Fine particulate matter (PM2.5) samples were collected using a high-volume air sampler and pre-combusted quartz filters during May 2013 to January 2014 at a background rural site (47 ∘ 35 N, 133 ∘ 31 E) in Sanjiang Plain, Northeast China. A homologous series of dicarboxylic acids (C 2 -C 11 ) and related compounds (oxoacids, α-dicarbonyls and fatty acids) were analyzed by using a gas chromatography (GC) and GC-MS method employing a dibutyl ester derivatization technique. Intensively open biomass-burning (BB) episodes during the harvest season in fall were characterized by high mass concentrations of PM2.5, dicarboxylic acids and levoglucosan. During the BB period, mass concentrations of dicarboxylic acids and related compounds were increased by up to >20 times with different factors for different organic compounds (i.e., succinic (C 4 ) acid > oxalic (C 2 ) acid > malonic (C 3 ) acid). High concentrations were also found for their possible precursors such as glyoxylic acid ( ω C 2 ), 4-oxobutanoic acid, pyruvic acid, glyoxal, and methylglyoxal as well as fatty acids. Levoglucosan showed strong correlations with carbonaceous aerosols (OC, EC, WSOC) and dicarboxylic acids although such good correlations were not observed during non-biomass-burning seasons. Our results clearly demonstrate biomass burning emissions are very important contributors to dicarboxylic acids and related compounds. The selected ratios (e.g., C 3 /C 4 , maleic acid/fumaric acid, C 2 / ω C 2 , and C 2 /levoglucosan) were used as tracers for secondary formation of organic aerosols and their aging process. Our results indicate that organic aerosols from biomass burning in this study are fresh without substantial aging or secondary production. The present chemical characteristics of organic compounds in biomass-burning emissions are very important for better understanding the impacts of biomass burning on the atmosphere aerosols. [ABSTRACT FROM AUTHOR]

From 2013, a significant decline in fine particulate matter (PM 2.5) occurred in most Chinese cities. In Nanjing, a capital city in the central of the Yangtze River Delta (YRD) region, the mass concentrations of total carbon (TC) in PM 2.5 decreased by approximately 48% during wintertime from 2014 to 2019. To provide detailed information in this trend, source apportionment of TC was carried out using a radiocarbon-(14C-) based method. In general, the average mass concentrations (and fossil fuel proportions) of TC, organic carbon (OC) and elemental carbon (EC) in six winters were 16.3 ± 8.5 μg m−3 (51%), 14.4 ± 7.8 μg m−3 (48%) and 2.0 ± 1.2 μg m−3 (65%), respectively. From 2014 to 2019, the reduction in TC was mainly attributed to the decline in non-fossil sources (6.4, 6.3–6.5 μg m−3) rather than fossil-fuel sources (3.6, 3.4–3.7 μg m−3) (medians, 10th-90th percentiles). The reduction of OC (9.1 μg m−3) was mainly attributed to OC from biomass burning (5.3, 4.6–6.1 μg m−3) and secondary formation from fossil-fuel sources (3.3, 2.6–3.9 μg m−3). Although the inter-annual variations for EC were less obvious, the reduction was dominated by the variations in non-fossil emissions (i.e., biomass burning). This study highlights the important role of non-fossil source control in the reduction of TC mass concentration in the YRD. Strategies of future emission control may pay more attention to both biomass burning emissions and secondary organic aerosols from precursors originating from fossil sources. [Display omitted] •Source apportionment was carried out using a14C-based method for six winters. •Nearly 2/3 of the declined TC was attributed to the decrease of non-fossil emissions. •Reduction of SOC ff should be considered more in the future. [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]

Radiocarbon ( 14 C) measurements of both organic carbon (OC) and elemental carbon (EC) allow a more detailed source apportionment, leading to a full and unambiguous distinction and quantification of the contributions from non-fossil and fossil sources. A thermal-optical method with a commercial OC/EC analyzer to isolate water-insoluble OC (WIOC) and EC for their subsequent 14 C measurement was applied for the first time to filtered precipitation samples collected at a costal site in Portugal and at a continental site in Switzerland. Our results show that WIOC in precipitation is dominated by non-fossil sources such as biogenic and biomass-burning emissions regardless of rain origins and seasons, whereas EC sources are shared by fossil-fuel combustion and biomass burning. In addition, monthly variation of WIOC in Switzerland was characterized by higher abundance in warm than in cold seasons, highlighting the importance of biogenic emissions to particulate carbon in rainwater. Samples with high particulate carbon concentrations in Portugal were found to be associated with increased biogenic input. Despite the importance of non-fossil sources, fossil emissions account for approximately 20% of particulate carbon in wet deposition for our study, which is in line with fossil contribution in bulk rainwater dissolved organic carbon as well as aerosol WIOC and EC estimated by the 14 C approach from other studies. [ABSTRACT FROM AUTHOR]

Elemental carbon (EC) or black carbon (BC) in the atmosphere has a strong influence on both climate and human health. In this study, radiocarbon (14C) based source apportionment is used to distinguish between fossil fuel and biomass burning sources of EC isolated from aerosol filter samples collected in Beijing from June 2010 to May 2011. The 14C results demonstrate that EC is consistently dominated by fossil-fuel combustion throughout the whole year with a mean contribution of 79% ± 6% (ranging from 70% to 91%), though EC has a higher mean and peak concentrations in the cold season. The seasonal molecular pattern of hopanes (i.e., a class of organic markers mainly emitted during the combustion of different fossil fuels) indicates that traffic-related emissions are the most important fossil source in the warm period and coal combustion emissions are significantly increased in the cold season. By combining 14C based source apportionment results and picene (i.e., an organic marker for coal emissions) concentrations, relative contributions from coal (mainly from residential bituminous coal) and vehicle to EC in the cold period were estimated as 25 ± 4% and 50 ± 7%, respectively, whereas the coal combustion contribution was negligible or very small in the warm period. [ABSTRACT FROM AUTHOR]

Radiocarbon (14C) 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 14C in micro-scale (μg) WSOC aerosol samples is successfully developed, which includes three steps: (1) extraction (2) freeze drying, and (3) online 14C analysis of CO2 from WSOC combustion. Procedure blanks are carefully assessed by measuring high-purity water and reference materials. Accurate 14C results could be obtained for WSOC with only 10 μg C, and thus the potential applications are substantially broadened because much less filter material is needed compared to previous 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 substantial 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. [ABSTRACT FROM AUTHOR]

Humic-like substances (HULIS), as important components of brown carbon (BrC), play an important role in climate change. In this study, one-year PM 2.5 samples from 2017 to 2018 were collected at Nanjing, China and the water soluble HULIS and other chemical species were analyzed to investigate the seasonal variations, optical properties and possible sources. The HULIS concentrations exhibited highest in winter and lowest in summer. The annual averaged HULIS concentration was 2.61 ± 1.79 μg m−3, accounting for 45 ± 13% of water-soluble organic carbon (WSOC). The HULIS light absorption coefficient at 365 nm (Abs 365, HULIS) averagely accounted for 71 ± 19% of that of WSOC, suggesting that HULIS are the main light-absorbing components in WSOC. The annual averaged Ångström absorption exponent and mass absorption efficiency of HULIS at 365 nm were 5.22 ± 0.77 and 1.71 ± 0.70 m2 g−1. Good correlations between HULIS with levoglucosan and K+ suggested biomass burning (BB) influence on HULIS. High concentrations of HULIS and secondary species (e.g., NO 3 −, SO 4 2−, NH 4 +, C 2 O 4 2−) were found in present of high relative humidity, indicating strong aqueous phase secondary HULIS formation. Secondary HULIS produced from anthropogenic and biogenic precursors were quantified based on the positive matrix factorization (PMF) model and the results showed that both fossil (55%) and biogenic (45%) emission sources made great contributions to HULIS. Fossil fuel combustion significantly contributed to HULIS formation throughout the whole year, which were enriched with more secondary HULIS (30%) than primary HULIS (25%). Strongest BB contribution (39%) was found in winter and biogenic SOA contribution (32%) was found in summer. A multiple linear regression (MLR) method was further applied to obtain specific source contributions to Abs 365, HULIS and the results showed that strong light-absorbing chromophores were produced from anthropogenic precursors. Our results highlight the anthropogenic SOA and fossil fuels combustion contributions to HULIS in addition to the biggest contributor, BB, in urban area in China. • Optical properties and sources of HULIS in PM 2.5 at Nanjing, China were explored. • High HULIS and secondary species levels were observed under high relative humidity. • Secondary HULIS from anthropogenic and biogenic precursors were quantified. • Both fossil (55%) and biogenic (45%) sources made great contributions to HULIS. • HULIS produced from anthropogenic precursors showed stronger UV absorption. [ABSTRACT FROM AUTHOR]

An increase in haze days has been observed in China over the past two decades due to the rapid industrialization, urbanization and energy consumptions. To address this server issue, Chinese central government has recently released the Action Plan on Prevention and Control of Air Pollution, which mainly focuses on regulation of indusial and transport-related emissions with major energy consumption from fossil fuels. This comprehensive and toughest plan is definitely a major step in the right direction aiming at beautiful and environmental-friendly China; however, based on recent source apportionment results, we suggest that strengthening regulation emissions from biomass-burning sources in both urban and rural areas is needed to meet a rigorous reduction target. Here, household biofuel and open biomass burning are highlighted, as impacts of these emissions can cause local and regional pollution. [ABSTRACT FROM AUTHOR]

Combination of near daily 3 m red, green, blue, and near infrared (NIR) Planetscope reflectance with lower temporal resolution 10 m and 20 m red, green, blue, NIR, red-edge, and shortwave infrared (SWIR) Sentinel-2 reflectance provides potential for improved global monitoring. Sharpening the Sentinel-2 reflectance with the Planetscope reflectance may enable near-daily 3 m monitoring in the visible, red-edge, NIR, and SWIR. However, there are two major issues, namely the different and spectrally nonoverlapping bands between the two sensors and surface changes that may occur in the period between the different sensor acquisitions. They are examined in this study that considers Sentinel-2 and Planetscope imagery acquired one day apart over three sites where land surface changes due to biomass burning occurred. Two well-established sharpening methods, high pass modulation (HPM) and Model 3 (M3), were used as they are multiresolution analysis methods that preserve the spectral properties of the low spatial resolution Sentinel-2 imagery (that are better radiometrically calibrated than Planetscope) and are relatively computationally efficient so that they can be applied at large scale. The Sentinel-2 point spread function (PSF) needed for the sharpening was derived analytically from published modulation transfer function (MTF) values. Synthetic Planetscope red-edge and SWIR bands were derived by linear regression of the Planetscope visible and NIR bands with the Sentinel-2 red-edge and SWIR bands. The HPM and M3 sharpening results were evaluated visually and quantitatively using the Q2n metric that quantifies spectral and spatial distortion. The HPM and M3 sharpening methods provided visually coherent and spatially detailed visible and NIR wavelength sharpened results with low distortion (Q2n values > 0.91). The sharpened red-edge and SWIR results were also coherent but had greater distortion (Q2n values > 0.76). Detailed examination at locations where surface changes between the Sentinel-2 and the Planetscope acquisitions occurred revealed that the HPM method, unlike the M3 method, could reliably sharpen the bands affected by the change. This is because HPM sharpening uses a per-pixel reflectance ratio in the spatial detail modulation which is relatively stable to reflectance changes. The paper concludes with a discussion of the implications of this research and the recommendation that the HPM sharpening be used considering its better performance when there are surface changes. [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]

Delhi, the capital city of India, experiences severe air pollution and suffers from its adverse effects on human health and ecosystems. This pollution is characterized by high levels of pollutants, including atmospheric nitrogen in both the gaseous and particulate phases. However, there is a lack of simultaneous measurement of chemical composition, tracers and 15N data in aerosols to understand the influence of different sources on N aerosols over Delhi. Here, we measured total nitrogen (TN), water-soluble total nitrogen (WSTN), water-soluble inorganic nitrogen (WSIN), and N stable isotope compositions (δ15N) in PM 2.5 samples covering the post-monsoon, winter, and summer periods of the year 2018–19. NH 4 +-N was the major N species, accounting for an average 58% of TN and 68% of WSIN. The temporal variations of TN, WSTN, NH 4 +-N, NO 3 −-N, and WSON showed peaks in the post-monsoon and winter seasons, exhibiting seasonality similar to PM 2.5 and levoglucosan (a biomass-burning tracer) indicating their co-genetic sources. Based on the correlation analysis between δ15N and N-species, we identified two distinct secondary chemical processes: i) in an NH 4 +-poor atmosphere, the gas-to-particle (NH 3 → NH 4 +) conversion and subsequent formation of NH 4 HSO 4 was the main process controlling the 15N and nitrogen enrichments in PM 2.5 ; whereas ii) under NH 4 +-rich conditions, the formation and dissociation of NH 4 NO 3 dominated. The coupled HYSPLIT and PSCF analyses highlighted the transport and contributions of open biomass burning emissions under a northwesterly atmospheric flow during post-monsoon as well as from local biomass combustion (from cooking and heating) during winter in the city and its vicinity. Our results suggested that i) both NH 4 +-N and NO 3 −-N were mainly impacted by biomass combustion during post-monsoon and winter seasons, and ii) NO 3 −-N resulted of dust transport from the Thar Desert in the summer season, but not NH 4 +-N. Finally, we recommend that future research focuses on the study of the seasonality of atmospheric nitrogen composition using 15N data from their different sources to design tailor-made measures and policies regarding the different potential sources, combining them within a comprehensive framework to ultimately improve air quality and the living environment in Delhi. • NH 4 +-N was the major N species, accounting for an average of 58% of TN. • NH 3 to NH 4 +conversion and formation of NH 4 HSO 4 dominated in NH 4 +-poor atmosphere. • Under NH 4 +-rich conditions, the formation and dissociation of NH 4 NO 3 dominated. • NH 4 +-N was mainly impacted by biomass combustions. • NO 3 −-N was related to both biomass burning and dust transport. [ABSTRACT FROM AUTHOR]

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, PM2.5 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 (ECf), BB-derived EC (ECbb), fossil-derived primary and secondary organic carbon (POCf, SOCf), BB-derived OC (OCbb) and the remaining OC (OCnf, other). The fractions of ECbb generally prevailed over ECf throughout the year. OCbb 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 POCf showed a spatial difference with a higher contribution at CMU, while SOCf displayed a temporal variation with a greater fraction in LBB. OCnf, other was originated from biogenic secondary aerosols, cooking emissions and bioaerosols as resolved by the principal component analysis with multiple liner regression model. The OCnf, 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.

Atmospheric hazardous volatile organic compounds (HVOCs) have adverse effects on human health. Health risks derived from inhalation of HVOCs have been widely assessed in Chinese cities, however, source-specific health risk analysis has been rarely done. In this work, the five intensive campaigns for monitoring HVOCs concentrations were conducted in Nanjing between July 2018 and May 2020. These datasets were further used to assess the health risks at the receptor site. The result showed that the average HVOCs concentration was 16.7 ± 20.0 ppb with higher levels in the autumn and winter. HVOCs concentrations exhibited diurnal cycles and peaked at the daytime/nighttime rush-traffic hours. By using the observed HVOCs data, the total lifetime cancer risk (LCR T) and hazard quotient (HQ T) were estimated to be 1.23 × 10−3 and 2.3, respectively, indicating the significant cancer risk and non-cancer risk at the receptor site. 1,1,2,2-tetrachloroethane (67%) was the major species to cancer risk while 1,2-dichloropropane (40%) was the dominant compound of non-cancer risk. Positive matrix factorization (PMF) model was used to resolve the source of HVOCs into vehicle emissions (29%), chemical petroleum (19%), solvent usage (17%), biomass burning (12%), coal combustion (10%), liquefied petroleum gas (9%) and fuel evaporation (4%). By combining the health risk assessments and source apportionment results, we finally concluded that solvent usage dominated both cancer risk and non-cancer risk of exposure to HVOCs at the receptor site. Thus, how to make the control measures to reduce HVOCs emissions from solvent usage will be an important issue for decreasing health risks in this polluted city. [Display omitted] • Significant cancer risk (1.23 × 10−3) and non-cancer risk (2.3) of exposure to HVOCs were found in Nanjing. • 1,1,2,2-tetrachloroethane and 1,2-dichloropropane were the major HVOCs species to health risks in Nanjing, respectively. • Solvent usage was the dominant source to 1,1,2,2-tetrachloroethane and 1,2-dichloropropane in Nanjing. • Solvent usage was the main source to health risks in Nanjing. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Water-soluble humic-like substances (HULIS ws) are a group of heterogeneous organic compounds in the atmosphere, greatly impacting climate change and human health. As the most significant biomass burning (BB) and fossil fuel burning polluted area in China, Northeast China Plain could generate more light absorbing HULIS ws to the atmosphere. In this work, daily fine particle (PM 2.5) samples were collected in Changchun, located in Northeast China Plain, from October 17th to November 29th, 2016, to investigate the potential sources of optical properties of HULIS ws. Here, the whole sampling period was divided into three sub-periods using the density of fire spots and the timeline of the central heating: the non-heating (October 17th to October 24th), early heating (October 25th to November 13th), and normal heating (November 14th to November 29th) periods. The mean mass concentrations of HULIS ws were 4.2 ± 1.2, 8.6 ± 3.6, and 2.4 ± 1.3 μg m−3 during the non-heating, early heating, and normal heating periods, respectively. The positive matrix factorization (PMF) model results suggested that the contribution of primary BB, secondary BB, and fossil fuel burning emissions were 46%, 24%, and 19% during the non-heating period, 22%, 29%, and 17% during the early heating period, and 13%, 16%, and 50% during the normal heating period, respectively. Combining the PMF results with the random forest (RF) algorithm, the contribution of each source to the optical properties was quantified. Here, BB still dominated the optical properties of HULIS ws in Northeast China. During the study period, the primary BB and secondary BB contributed 25% and 34% in the light absorption coefficient (Abs), 22% and 33% in the mass absorption exponent (MAE), and 17% and 33% in the absorption Ångström exponent (AAE), respectively. Other sources like cooking and fossil combustion contributed 25% and 35% in Abs, 35% and 26% in MAE, and 16% and 33% in AAE, respectively. • 72% biomass burning emission contributed 40%–50% to light absorption parameters. • 4% cooking emission contributed 16%–35% to light absorption parameters. • This work provides a fast and easy way to quantify the contribution of sources to the light absorption properties. [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]

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 k BrC (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 (IRF CAs) at the top of atmosphere (TOA) and 16 ± 3% to IRF CAs 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. • Including BrC in model reduces model bias of AAOD by 5–15%. • BrC contributes 33–40% to total carbonaceous aerosol absorption. • BrC strengthens 9 ± 5% of surface cooling effect of organic aerosols. [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]