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[Display omitted] Aerosol ammonium (NH 4 +), mainly produced from the reactions of ammonia (NH 3) with acids in the atmosphere, has significant impacts on air pollution, radiative forcing, and human health. Understanding the source and formation mechanism of NH 4 + can provide scientific insights into air quality improvements. However, the sources of NH 3 in urban areas are not well understood, and few studies focus on NH 3 /NH 4 + at different heights within the atmospheric boundary layer, which hinders a comprehensive understanding of aerosol NH 4 +. In this study, we perform both field observation and modeling studies (the Community Multiscale Air Quality, CMAQ) to investigate regional NH 3 emission sources and vertically resolved NH 4 + formation mechanisms during the winter in Beijing. Both stable nitrogen isotope analyses and CMAQ model suggest that combustion-related NH 3 emissions, including fossil fuel sources, NH 3 slip, and biomass burning, are important sources of aerosol NH 4 + with more than 60% contribution occurring on heavily polluted days. In contrast, volatilization-related NH 3 sources (livestock breeding, N-fertilizer application, and human waste) are dominant on clean days. Combustion-related NH 3 is mostly local from Beijing, and biomass burning is likely an important NH 3 source (∼15%–20%) that was previously overlooked. More effective control strategies such as the two-product (e.g., reducing both SO 2 and NH 3) control policy should be considered to improve air quality. [ABSTRACT FROM AUTHOR]

Biomass burning is one of the key sources of urban aerosols in the North China Plain, especially during winter, when the impact of secondary organic aerosols (SOAs) formed from biogenic volatile organic compounds (BVOCs) is generally considered to be minor. However, little is known about the influence of biogenic SOA loading on the molecular composition of wintertime organic aerosols. Here, we investigated the water-soluble organic compounds in fine particulate matter (PM 2.5) from urban Tianjin by ultrahigh-resolution Fourier transform ion cyclotron resonanc mass spectrometry (FT-ICR MS). Our results show that most of the CHO and CHON compounds are derived from biomass burning which are poor in oxygen and contain aromatic rings that probably contribute to light-absorbing brown carbon (BrC) chromophores. Under moderate to high SOA-loading conditions, the nocturnal chemistry is more efficient than photooxidation to generate secondary CHO and CHON compounds with high oxygen content. Under low SOA loading, secondary CHO and CHON compounds with low oxygen content are mainly formed by photochemistry. Secondary CHO compounds are mainly derived from oxidation of monoterpenes. However, nocturnal chemistry may be more productive to sesquiterpene-derived CHON compounds. In contrast, the number- and intensity-weight of S-containing groups (CHOS and CHONS) increased significantly with the increase of biogenic SOA loading, which agrees with the fact that a majority of the S-containing groups are identified as organosulfates (OSs) and nitrooxy–organosulfates (nitrooxy–OSs) that are derived from the oxidation of BVOCs. Terpenes may be potential major contributors to organosulfates and nitrooxy–organosulfates. While the nocturnal chemistry is more beneficial to the formation of organosulfates and nitrooxy–organosulfates under low SOA loading. The SOA loading is an important factor that is associated with the oxidation degree, nitrate group content and chemodiversity of nitrooxy-organosulfates. Furthermore, our study suggests that the hydrolysis of nitrooxy-organosulfates is a possible pathway for the formation of organosulfates. [ABSTRACT FROM AUTHOR]

Brown carbon (BrC) aerosols exert vital impacts on climate change and atmospheric photochemistry due to their light absorption in the wavelength range from near-ultraviolet (UV) to visible light. However, the optical properties and formation mechanisms of ambient BrC remain poorly understood, limiting the estimation of their radiative forcing. In the present study, fine particles (PM 2.5) were collected during 2016–2017 on a day/night basis over urban Tianjin, a megacity in northern China. Light absorption and fluorescence properties of water extracts of PM 2.5 were investigated to obtain seasonal and diurnal patterns of atmospheric water-soluble BrC. There were obvious seasonal, but no evident diurnal, variations in the light absorption properties of BrC. In winter, BrC showed much stronger light-absorbing ability, with a mass absorption efficiency at 365 nm (MAE 365) in winter (1.54±0.33 m 2 gC -1) that was 1.8 times larger than MAE 365 in summer (0.84±0.22 m 2 gC -1). Direct radiative effects by BrC absorption relative to black carbon in the UV range were 54.3±16.9 % and 44.6±13.9 % in winter and summer, respectively. In addition, five fluorescent components in BrC, including three humic-like fluorophores and two protein-like fluorophores were identified with excitation–emission matrix fluorescence spectrometry and parallel factor (PARAFAC) analysis. The less oxygenated components contributed more to winter and nighttime samples, while more oxygenated components increased in summer and daytime samples. The higher humification index (HIX), together with lower biological index (BIX) and fluorescence index (FI), suggests that the chemical compositions of BrC were associated with a high aromaticity degree in summer and daytime due to photobleaching. Fluorescent properties indicate that wintertime BrC were predominantly affected by primary emissions and fresh secondary organic aerosol (SOA), while summer ones were more influenced by aging processes. Results of source apportionments using organic molecular compositions of the same set of aerosols reveal that fossil fuel combustion and aging processes, primary bioaerosol emission, biomass burning, and biogenic and anthropogenic SOA formation were the main sources of BrC. Biomass burning contributed much more to BrC in winter and at nighttime, while biogenic SOA contributed more in summer and during the daytime. In particular, our study highlights that primary bioaerosol emission is an important source of BrC in urban Tianjin in summer. [ABSTRACT FROM AUTHOR]

Amino acids (AAs) are involved in the global nitrogen cycle and are important components of nitrogenous organic aerosols. Protein and free amino acid (FAA) concentrations in total suspended particulate (TSP) and their major emission sources were investigated in spring and autumn at Mount Tai (Mt. Tai) on the North China Plain and the nearby city named Liaocheng. There were significant spatial and seasonal differences in protein and FAA concentrations, with rainfall producing lower concentrations. For chiral isomers of AAs, there were significant diurnal differences in D/L-Methionine (Met), which was probably due to FAA source differences caused by regional valley winds and background winds. The high D/L-aspartic acid (Asp) and D/L-glutamine (Glu) concentrations may be indicative of the important contributions of chunk and honeycomb coal combustion. Stable nitrogen isotope analyses revealed that plant debris, soil dust, and biomass burning were important sources of glycine (Gly). Biomass burning, as well as chunk and honeycomb coal combustion, produced large amounts of L-arginine (Arg). Soil dust was the dominant source of FAAs for both Mt. Tai and Liaocheng, while biomass burning contributed more in autumn, and the proportional contribution of plant debris increased in spring. [Display omitted] • Molecular compositions and sources of atmospheric free amino acids in mountainous and urban aerosols were compared. • D/L ratio and stable nitrogen isotope analyses were used together to determine the source of particulate free amino acids. • Mechanism of regional transport of particulate free amino acids in mountainous area is proposed. [ABSTRACT FROM AUTHOR]

Nitrogen-containing species are major components in atmospheric aerosols. However, little is known about the sources of N-containing aerosols over high mountainous regions, especially for organic nitrogen (ON). This study aims to reveal the emission sources of both inorganic and organic nitrogen in tropospheric aerosols atop Mt. Tai, China, and to improve our understanding of the N cycle imbalance in the North China Plain (NCP). Total suspended particle (TSP) samples were collected on a daytime/nighttime basis in spring 2017 and were investigated for the concentrations and stable N isotopic compositions of total nitrogen, NH4+, NO3− and ON. Our results show that the concentrations of N-containing compounds were higher in daytime than nighttime, mainly resulting from mountain–valley breezes and the changes of planetary boundary layer height. However, no significant day/nighttime changes were found for their corresponding δ15N values, indicating similar contributions from different N sources between day and night. The MixSIAR Bayesian stable isotope mixing model results suggest that the most important emission source of NH3 for aerosol NH4+ was agriculture, followed by fossil fuel-related sources, human waste and biomass burning. Aerosol NO3− was mainly formed from combustion and mobile emitted NOx. Interestingly, the isotopes of ON suggest that ON were very likely firstly of primary origin. Our study reveals the characteristics of reactive N emission sources and helps understand the regional transport of tropospheric N-containing aerosols in the NCP. [ABSTRACT FROM AUTHOR]

Biomass burning and primary biological aerosol particles account for an important part of urban aerosols. Floods of studies have been conducted on the chemical compositions of fine aerosols (PM 2.5) in megacities where the haze pollution is one of the severe environmental issues in China. However, little is known about their size distributions in atmospheric aerosols in the urban boundary layer. Here, size-segregated aerosol samples were collected in Beijing during haze and clear days from April 2017 to January 2018. Three anhydrosugars, six primary saccharides and four sugar alcohols in these samples were identified and quantified by gas chromatography/mass spectrometry (GC/MS). Higher concentrations of a biomass burning tracer, levoglucosan, were detected in autumn and winter than in other seasons. Sucrose, glucose, fructose, mannitol and arabitol were more abundant in the bloom and glowing seasons. A particularly high level of trehalose was found in spring, which was largely associated with the Asian dust outflows. Anhydrosugars, xylose, maltose, inositol and erythritol are mainly present in the fine mode (<2.1 µ m), while the others showed the coarse-mode preference. The concentrations of measured tracers of biomass burning particles and primary biological particles in the haze events were higher than those in the non-hazy days, with enrichment factors of 2–10. Geometric mean diameters (GMDs) of molecular markers of biomass burning and primary biological aerosols showed that there was no significant difference in the coarse mode (>2.1 µ m) between the haze and non-haze samples, while a size shift towards large particles and large GMDs in the fine fraction (<2.1 µ m) was detected during the hazy days, which highlights that the stable meteorological conditions with high relative humidity in urban Beijing may favor the condensation of organics onto coarse particles.The contributions of reconstructed primary organic carbon (POC) by tracer-based methods from plant debris, fungal spores and biomass burning to aerosol OC in the total-mode particles were in the ranges of 0.09 %–0.30 % (on average 0.21 %), 0.13 %–1.0 % (0.38 %) and 1.2 %–7.5 % (4.5 %), respectively. This study demonstrates that the contribution of biomass burning was significant in Beijing throughout the whole year with the predominance in the fine mode, while the contributions of plant debris and fungal spores dominated in spring and summer in the coarse mode, especially in sizes >5.8 µ m. Our observations demonstrate that the sources, abundance and chemical composition of urban aerosol particles are strongly size dependent in Beijing, which is important to better understand the environmental and health effects of urban aerosols and should be considered in air quality and climate models. [ABSTRACT FROM AUTHOR]

In order to better understand the molecular composition and sources of organic aerosols in Tianjin, a coastal megacity in North China, ambient fine aerosol (PM 2.5) samples were collected on a day/night basis from November to December 2016 and from May to June 2017. The organic molecular composition of PM 2.5 components, including aliphatic lipids (n -alkanes, fatty acids, and fatty alcohols), sugar compounds, and photooxidation products from isoprene, monoterpene, β -caryophyllene, naphthalene, and toluene, was analysed using gas chromatography–mass spectrometry. Fatty acids, fatty alcohols, and saccharides were identified as the most abundant organic compound classes among all of the tracers detected in this study during both seasons. High concentrations of most organics at night in winter may be attributed to intensive residential activities such as house heating as well as the low nocturnal boundary layer height. Based on tracer methods, the contributions of the sum of primary and secondary organic carbon (POC and SOC respectively) to aerosol organic carbon (OC) were 24.8 % (daytime) and 27.6 % (night-time) in winter and 38.9 % (daytime) and 32.5 % (night-time) in summer. In detail, POC derived from fungal spores, plant debris, and biomass burning accounted for 2.78 %–31.6 % (12.4 %; please note that values displayed in parentheses in the following are average values) of OC during the daytime and 4.72 %–45.9 % (16.3 %) at night in winter, and 1.28 %–9.89 % (5.24 %) during the daytime and 2.08 %–47.2 % (10.6 %) at night in summer. Biomass-burning-derived OC was the predominant source of POC in this study, especially at night (16.0±6.88 % in winter and 9.62±8.73 % in summer). Biogenic SOC from isoprene, α - /β -pinene, and β -caryophyllene exhibited obvious seasonal and diurnal patterns, contributing 2.23±1.27 % (2.30±1.35 % during the daytime and 2.18±1.19 % at night) and 8.60±4.02 % (8.98±3.67 % and 8.21±4.39 %) to OC in winter and summer respectively. Isoprene and α - /β -pinene SOC were obviously elevated in summer, especially during the daytime, mainly due to strong photooxidation. Anthropogenic SOC from toluene and naphthalene oxidation showed higher contributions to OC in summer (21.0±18.5 %) than in winter (9.58±3.68 %). In summer, toluene SOC was the dominant contributor to aerosol OC, and biomass burning OC also accounted for a high contribution to OC, especially at night-time; this indicates that land/sea breezes also play an important role in the aerosol chemistry of the coastal city of Tianjin in North China. [ABSTRACT FROM AUTHOR]

Lipids are important biogenic markers to indicate the sources and chemical process of aerosol particles in the atmosphere. To better understand the influences of biogenic and anthropogenic sources on forest aerosols, total suspended particles (TSP) were collected at Mt. Changbai, Shennongjia, and Xishuangbanna that are located at different climatic zones in northeastern, central and southwestern China. n- Alkanes, fatty acids and n- alcohols were detected in the forest aerosols based on gas chromatography-mass spectrometry. The total concentrations of aliphatic compounds ranged from 15.3 ng m−3 to 566 ng m−3, and fatty acids were the most abundant (44–95%) followed by n- alkanes and n- alcohols. Low molecular weight- (LFAs) and unsaturated fatty acids (UnFAs) showed diurnal variation with higher concentrations during the nighttime in summer, indicating the potential impact from microbial activities on forest aerosols. The differences of oleic acid (C 18:1) and linoleic acid (C 18:2) concentrations between daytime and nighttime increased at lower latitude, indicating more intense photochemical degradation occurred at lower latitude regions. High levels of n- alkanes during daytime in summer with higher values of carbon preference indexes, combining the strong odd carbon number predominance with a maximum at C 27 or C 29 , implied the high contributions of biogenic sources, e.g., higher plant waxes. In contrast, higher concentrations of low molecular weight n- alkanes were detected in winter forest aerosols. Levoglucosan showed a positive correlation (R2 > 0.57) with high- and low molecular weight aliphatic compounds in Mt. Changbai, but such a correlation was not observed in Shennongjia and Xishuangbanna. These results suggest the significant influence of biomass burning in Mt. Changbai, and fossil fuel combustion might be another important anthropogenic source of forest aerosols. This study adds useful information to the current understanding of forest organic aerosols at different geographical locations in China. [Display omitted] • Seasonal differences in impact of biogenic/anthropogenic sources on forest aerosols. • The photodegradation of unsaturated fatty acids was more severe in lower latitudes. • Both biomass burning and fossil fuel combustion contributed to the Mt. Changbai aerosols. • Different patterns of lipids in forest aerosols at different locations in China. [ABSTRACT FROM AUTHOR]

Black carbon (BC) plays a vital role in atmospheric environment and climate change. Temporal variations and transport pathways of BC in Xiamen, China with the impacts of synoptic circulation were investigated in 2014 with Aethalometer. Annual mean BC concentration was 4270 ng m−3. BC exhibited clear diurnal (seasonal) variations, with the maximum of 6182 (4755) ng m−3 at 6:00 (in spring) and minimum of 2847 (3774) ng m−3 at 13:00 (in summer). Conditional probability function analysis indicated that high BC concentrations were associated with northwesterly winds with low wind speed. Air masses originating from the East China Sea and passing along with East China Coast had the highest BC concentrations. Potential source contribution function and concentration weighted trajectory analysis suggested that major sources for BC included the surrounding region, southwestern Fujian and eastern Guangdong to the southwest, Hubei, Hunan and Jiangxi to the northwest, the East China Sea and the South China Sea. Of the nine synoptic circulation patterns, three cyclone-related patterns were associated with low BC concentrations and small biomass burning (BC bb) contributions. Of the six anticyclone-related patterns, the three cold-high circulations around winter were associated with moderate BC concentrations and large BC bb contributions. The two cold-high patterns in spring and autumn were associated with high BC concentrations and small BC bb contributions, while the warm-high pattern was associated with moderate BC concentration and small BC bb contribution. The findings provide insights into the transport mechanisms of BC with the impacts of synoptic pattern in China. • One year on-line observation of BC was conducted in Western Taiwan Strait in China. • Originations and transport pathways of BC were investigated with CPF, PSCF and CWT. • Impacts of synoptic circulations on BC from different source sectors were analyzed. [ABSTRACT FROM AUTHOR]

• Rainwater DOM along the yangtze river were characterized by optical properties and FT-ICR MS. • Natural and anthropogenic emissions and climatic conditions shaped the chemodiversity of rainwater DOM. • Biogenic secondary organic compounds widely contributed to rainwater DOM along the Yangtze River Basin. Rainwater dissolved organic matter (DOM) plays an important role in the biogeochemical cycle and evolution of organic matter in the land-atmosphere interface. To better understand their sources and molecular composition in the atmosphere, rainwater samples were collected at six different locations along the Yangtze River Basin. Based on the application of a combined approach including excitation-emission matrix (EEM) fluorescence and Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS), various sources (terrestrial, anthropogenic, and autochthonous sources) of rainwater DOM were revealed. Results show that the derivatives of biogenic volatile organic compounds were widely distributed and contributed to rainwater DOM along the Yangtze River Basin. In the up-river city Batang, rainwater DOM was affected by the long-range atmospheric transport due to the Indian summer monsoon. Lijiang, a city on the southeastern edge of Tibetan plateau, was related to strong local biomass burning. The industrial cities of Panzhihua and Luzhou showed large differences in organic composition due to distinct industrial types. Fuling, a district in Chongqing Municipality, was significantly contributed by aged organics from biomass burning. While rainwater DOM in Shanghai, a coastal megacity, contained a high fraction of sea spray organics. Further, more than 70% of rainwater DOM molecules are associated with 36 typical transformation mechanisms during rainwater-scavenging processes, e.g., oxidation reactions, dealkylation and decarboxylation. Our study demonstrates that local natural and anthropogenic emissions and climatic conditions strongly shaped the chemodiversity and possible precursor-product pairs of rainwater DOM along the Yangtze River Basin, which helps to better understand the biogeochemical cycles of organic matter in a large-scale watershed under the influence of human activities. [Display omitted] [ABSTRACT FROM AUTHOR]