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Secondary organic aerosol (SOA) plays a significant role in atmospheric chemistry. However, little is known about the vertical profiles of SOA in the urban boundary layer (UBL). This knowledge gap constrains the SOA simulation in chemical transport models. Here, the aerosol samples were synchronously collected at 8, 120, and 260 m based on a 325 m meteorological tower in Beijing from 15 August to 10 September 2015. Strict emission controls were implemented during this period for the 2015 China Victory Day parade. Here, we observed that the total concentration of biogenic SOA tracers increased with height. The fraction of SOA from isoprene oxidation increased with height, whereas the fractions of SOA from monoterpenes and sesquiterpenes decreased, and 2,3-dihydroxy-4-oxopentanoic acid (DHOPA), a tracer of anthropogenic SOA from toluene oxidation, also increased with height. The complicated vertical profiles of SOA tracers highlighted the need to characterize SOA within the UBL. The mass concentration of estimated secondary organic carbon (SOC) ranged from 341 to 673 ng C m−3. The increase in the estimated SOC fractions from isoprene and toluene with height was found to be more related to regional transport, whereas the decrease in the estimated SOC from monoterpenes and sesquiterpene with height was more subject to local emissions. Emission controls during the parade reduced SOC by 4 %–35 %, with toluene SOC decreasing more than the other SOC. This study demonstrates that vertical distributions of SOA within the UBL are complex, and the vertical profiles of SOA concentrations and sources should be considered in field and modeling studies in the future.

Little is known about the formation processes of nitrooxy organosulfates (OSs) by nighttime chemistry. Here we characterize nitrooxy OSs at a molecular level in firework-related aerosols in urban Beijing during Chinese New Year. High-molecular-weight nitrooxy OSs with relatively low H / C and O / C ratios and high unsaturation are potentially aromatic-like nitrooxy OSs. They considerably increased during New Year's Eve, affected by the firework emissions. We find that large quantities of carboxylic-rich alicyclic molecules possibly formed by nighttime reactions. The sufficient abundance of aliphatic-like and aromatic-like nitrooxy OSs in firework-related aerosols demonstrates that anthropogenic volatile organic compounds are important precursors of urban secondary organic aerosols (SOAs). In addition, more than 98 % of those nitrooxy OSs are extremely low-volatility organic compounds that can easily partition into and consist in the particle phase and affect the volatility, hygroscopicity, and even toxicity of urban aerosols. Our study provides new insights into the formation of nitrooxy organosulfates from anthropogenic emissions through nighttime chemistry in the urban atmosphere.

Cold formed steel (CFS) built-up members are increasingly used in buildings because of their better mechanical performance. In this paper, the elastic buckling behaviors of the composite plates extracted from CFS back-to-back built-up columns were investigated using a combination of tests and finite element (FE) analyses. A total of 18 CFS back-to-back built-up columns were tested in this study. The built-up sections were fabricated from two identical C-section components and were assembled with self-drilling screws at their webs. The effects of screw number and screw spacing on the critical buckling loads and buckling modes of the built-up column were investigated in this paper. Moreover, extensive parametric studies were conducted in detail by developing CFS FE models based on the validation process with available experimental results. In addition, both the critical buckling loads as well as the buckling modes predicted from the FE analyses were in good agreement with the laboratory test results.

In this paper, a new fractional-order complex chaotic system (FOCCS) is proposed and studied. Firstly, the dissipativity and stability are discussed. Secondly, the dynamical characteristics of the system with parameters and order changes are analyzed by using phase diagrams, Lyapunov exponent (LEs) and bifurcation diagrams, respectively. In addition, the dynamical behavior is discussed for q of integer and fractional orders. In particular, the attractor coexistence is found, such as the coexistence of chaotic attractor and chaotic attractor, and chaotic attractor and periodic attractor. Interestingly, the multiple attractors coexistence is found by changing the initial conditions with fixed parameters. Finally, it is implemented on the analog circuit and DSP platform. The study provide a reference for the research and application of chaos.

Measurements of OH, HO2, complex RO2 (alkene- and aromatic-related RO2) and total RO2 radicals taken during the integrated Study of AIR Pollution PROcesses in Beijing (AIRPRO) campaign in central Beijing in the summer of 2017, alongside observations of OH reactivity, are presented. The concentrations of radicals were elevated, with OH reaching up to 2.8×107moleculecm-3, HO2 peaking at 1×109moleculecm-3 and the total RO2 concentration reaching 5.5×109moleculecm-3. OH reactivity (k(OH)) peaked at 89 s−1 during the night, with a minimum during the afternoon of ≈22s-1 on average. An experimental budget analysis, in which the rates of production and destruction of the radicals are compared, highlighted that although the sources and sinks of OH were balanced under high NO concentrations, the OH sinks exceeded the known sources (by 15 ppbv h−1) under the very low NO conditions (

Biological aerosol particles play a crucial role in the Earth system, particularly in the land/ocean-atmosphere interactions. This paper aims to summarize the up-to-date research progresses on the characteristics, biomarkers as well as the health-related, climatic and ecological effects of biological aerosol particles in polluted regions, especially in East Asia and South Asia. The atmospheric abundance, size distribution, and community structure of microorganisms show differences during haze and non-haze conditions. The long-distance transportation of dust-associated microorganisms influences the abundance and community structure of airborne microbes in downwind areas. Wildfire smoke or biomass burning potentially impacts the release, transport and dispersal of microorganisms in the atmosphere. Meteorological conditions and air pollutants likely interact with airborne microorganisms, pollen, and fluorescent biological aerosol particles. Molecular biomarkers including proteins and amino acids, sugars, and lipid compounds have been used to fingerprint the sources of biological aerosols and give important biogeochemical information of atmospheric aerosols. In addition to pathogenic and allergenic microorganisms and pollen, biological aerosol particles indicated by abundant endotoxins and antibiotic resistance genes could have significant impacts on public health. In polluted regions, the potential influences of biological aerosol particles on climate and ecosystems could be more complex. We comprehensively summarize the recent research progresses on the characteristics, biomarkers, influencing factors, and effects of biological aerosol particles in polluted regions, mostly in East Asia and South Asia. To further understand the complicated effects of biological aerosol particles in polluted regions, the development and application of novel approaches and techniques as well as in-depth investigations on the roles of biological aerosol particles in atmospheric chemistry, cloud formation, and public health need to be implemented.

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 (PM2.5) 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 PM2.5 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 (MAE365) in winter (1.54±0.33 m2 gC−1) that was 1.8 times larger than MAE365 in summer (0.84±0.22 m2 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.

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 33.2 ng m−3 to 520 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 (C18:1) and linoleic acid (C18:2) 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 C27 or C29, 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 Xishuangbanan. These results suggest the significant influence of biomass burning in Mt. Changbai, and fossil fuel combustion might be another important anthropogenic source in Northeast China. This study adds useful information to the current understanding of forest organic aerosols at different geographical locations in China.

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.

Strict emission controls were implemented in Beijing and the surrounding regions in the North China Plain to guarantee good air quality during the 2014 Asia-Pacific Economic Cooperation (APEC) summit. Thus, the APEC period provides a good opportunity to study the sources and formation processes of atmospheric organic aerosol. Here, fine particles (PM

Molecular compositions and stable carbon isotope ratios (δ13C) of n-alkanes and fatty acids (FA) were investigated in urban aerosols from Beijing, China. Seasonal trends for n-alkanes showed a high...

This study investigates the concentrations and δ15N values of NH4+ in PM2.5 at three heights (8, 120, and 260 m) on a 325 m tower in urban Beijing. NH4+ concentrations were lower during the Parade ...

Organic tracers are useful for investigating the sources of carbonaceous aerosols but there are still no adequate studies in China. To obtain insights into the diurnal variations, properties, and the influence of regional emission controls on carbonaceous aerosols in Beijing, day-/nighttime PM2.5 samples were collected before (Oct. 15th - Nov. 2nd) and during (Nov. 3rd - Nov. 12th) the 2014 Asia-Pacific Economic Cooperation (APEC) summit. Eleven organic compound classes were analysed using gas chromatography/mass spectrometry (GC/MS). In addition, the stable carbon isotope ratios (δ13CTC) of total carbon (TC) were detected using an elemental analyser/isotope ratio mass spectrometry (EA/irMS). Most of the organic compounds were more abundant during the night than in the daytime, and their concentrations generally decreased during the APEC. These features were associated with the strict regional emission controls and meteorological conditions. The day/night variations of δ13CTC were smaller during the APEC than those before the APEC the summit, suggesting that regionally transported aerosols are potentially played an important role in the loading of organic aerosols in Beijing before the APEC summit. The source apportionment based on the organic tracers suggested that biomass burning, plastic and microbial emissions, and fossil fuel combustion were important sources of organic aerosols in Beijing. Furthermore, a similar contribution of biomass burning to OC before and during the APEC suggests biomass burning was a persistent contributor to PM2.5 in Beijing and its surroundings.

Understanding how the sources of an atmospheric organic aerosol (OA) govern its burden is crucial for assessing its impact on the environment and adopting proper control strategies. In this study, the sources of OA over Beijing were assessed year-around based on the combination of two separation approaches for OA, one from chemical fractionation into the high-polarity fraction of water-soluble organic matter (HP-WSOM), humic-like substances (HULIS), and water-insoluble organic matter (WISOM), and the other from statistical grouping using positive matrix factorization (PMF) of high-resolution aerosol mass spectra. Among the three OA fractions, HP-WSOM has the highest O/C ratio (1.36), followed by HULIS (0.56) and WISOM (0.17). The major sources of different OA fractions were distinct: HP-WSOM was dominated by more oxidized oxygenated OA (96%); HULIS by cooking-like OA (40%), less oxidized oxygenated OA (27%), and biomass burning OA (21%); and WISOM by fossil fuel OA (77%). In addition, our results provide evidence that mass spectral-based PMF factors are associated with specific substructures in molecules. These structures are further discussed in the context of the FT-IR results. This study presents an overall relationship of OA groups monitored by chemical and statistical approaches for the first time, providing insights for future source apportionment studies.

Atmospheric aerosol affects the Earth’s radiation budget by directly scattering and absorbing solar radiation and indirectly acting as cloud condensation nuclei. Both of the effects are responsible for the uncertainties in the prediction of global climate change. A better understanding of the hygroscopicity of the organic aerosol is important because it is poorly characterized to date. In this study, the hygroscopicity of humic-like substances (HULIS), a ubiquitous mixture of water-soluble organic matter, isolated from aerosol samples collected in Beijing in different seasons, was measured using a hygroscopicity tandem differential mobility analyzer (HTDMA). The hygroscopicity parameter of the isolated HULIS fraction (κHULIS) was in the range of 0.03–0.13 (mean: 0.06). Considering the possible influence from small amounts of inorganic salts, the hygroscopicity parameter of pure organic HULIS (κ*HULIS) was found to be slightly lower (0–0.11, mean: 0.04). The κHULIS showed a seasonal variation; the values were highest in summer (0.08), followed by spring (0.06), autumn (0.06), and winter (0.04). The κ*HULIS showed a similar seasonal variation, with the highest and lowest values in summer (0.07) and autumn (0.01), respectively. Both κHULIS and κ*HULIS were correlated positively with the O/C ratio of the HULIS. Comparison of the hygroscopicity parameter values with factors from positive matrix factorization (PMF) analysis of the mass spectra of the HULIS fractions showed that κHULIS correlated positively with more-oxidized oxygenated organic aerosol (MO-OOA) and less-oxidized OOA (LO-OOA), and correlated negatively with cooking-like OA (COA) and biomass burning OA (BBOA). The relationship between the hygroscopicity parameter and sources was further explored based on a multi-liner regression analysis. The variation in the hygroscopicity of HULIS and its connection to sources provide an insight into the contribution of organics to aerosol hygroscopicity, toward a better understanding of its link to climate.

Little is known about the formation processes of nitrooxy-organosulfates (nitrooxy-OSs) by nighttime chemistry. Here we characterize nitrooxy-OSs at a molecular level in firework-related aerosols in urban Beijing during Chinese New Year. High-molecular-weight nitrooxy-OSs with relatively low H / C and O / C ratios and high unsaturation, which are potentially aromatic-like nitrooxy-OSs, considerably increased during the New Year’s Eve. We find that large quantities of carboxylic-rich alicyclic molecules possibly formed by nighttime reactions. The sufficient abundance of aliphatic-like and aromatic-like nitrooxy-OSs demonstrates that both anthropogenic and biogenic volatile organic compounds are essential precursors of urban secondary organic aerosols (SOA). Besides, more than 98 % of nitrooxy-OSs were extremely low-volatile organic compounds that could easily partition into and consist in the particle phase, and affected the volatility, hygroscopicity, and even toxicity of urban aerosols. Our study provides new insights into the formation of nitrooxy-organosulfates from anthropogenic emissions through nighttime chemistry in the urban atmosphere.

Measurements of OH, HO2, RO2-complex (alkene and aromatic-related RO2) and total RO2 radicals taken during the AIRPRO campaign in central Beijing in the summer of 2017, alongside observations of OH reactivity are presented. The concentrations of radicals were elevated with OH reaching up to 2.8 × 107 molecule cm−3, HO2 peaked at 1 × 109 molecule cm−3 and the total RO2 concentration reached 5.5 × 109 molecule cm−3. OH reactivity (k(OH)) peaked at 89 s−1 during the night, with a minimum during the afternoons of ~ 22 s−1 on average. An experimental budget analysis, in which the rates of production and destruction of the radicals are compared, highlighted that although the sources and sinks of OH were balanced under high NO concentrations, the OH sinks exceeded the known sources (by 15 ppbv hr−1) under the very low NO conditions (

Firework (FW) emission has strong impacts on air quality and public health. However, little is known about the molecular composition of FW-related airborne particulate matter (PM) especially the organic fraction. Here we describe the detailed molecular composition of Beijing PM collected before, during, and after a FW event in New Year's Eve evening in 2012. Subgroups of CHO, CHNO, and CHOS were characterized using ultrahigh resolution Fourier transform-ion cyclotron resonance (FT-ICR) mass spectrometry. These subgroups comprise substantial fraction of aromatic-like compounds with low O/C ratio and high degrees of unsaturation, some of which plausibly contributed to the formation of brown carbon in Beijing PM. Moreover, we found that the number concentration of sulfur-containing compounds especially the organosulfates was increased dramatically by the FW event, whereas the number concentration of CHO and CHON doubled after the event. The co-variation of CHO, CHON, and CHOS subgroups was suggested to be associated with multiple atmospheric aging processes of aerosols including the multiphase redox chemistry driven by NOx, O3, and •OH. These findings highlight that FW emissions can lead to a sharp increase of high molecular weight compounds particularly aromatic-like substances in urban PM, which may affect the light absorption properties and adverse health effects of atmospheric aerosols.

In order to better understand the molecular composition and sources of organic aerosols in Tianjin, a coastal megacity in North China, ambient fine aerosol (PM2.5) samples were collected on a day/night basis from November to December 2016 and from May to June 2017. The organic molecular composition of PM2.5 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.

Pervasive particulate pollution has been observed over large areas of the North China Plain. The high level of sulfate, a major component in fine particles, is pronounced during heavy pollution periods. Being different from source apportionments by atmospheric chemistry-transport model and receptor modeling methods, here we utilize sulfur isotopes to discern the potential emission sources. Sixty-five daily PM2.5 samples were collected at an urban site in Beijing between September 2013 and July 2014. Inorganic ions, organic/elemental carbon and stable sulfur isotopes of sulfate were analyzed. The “fingerprint” characteristics of stable sulfur isotopic composition, together with trajectory clustering modeled by HYSPLIT-4 (HYbrid Single-Particle Lagrangian Integrated Trajectory) and FLEXPART (“FLEXible PARTicle dispersion model”), was employed to identify potential aerosol sources in Beijing. Results exhibited a distinctive seasonality with sulfate, nitrate, ammonium, organic matter, and element carbon being the dominant species of PM2.5. Elevated concentrations of chloride with high organic matter were found in autumn and winter as a result of enhanced fossil fuel (mainly coal) combustion. The δ34S values of the Beijing aerosols ranged from 2.8‰ to 9.9‰ with an average of 6.0 ± 1.8‰, further indicating that the major sulfur source was direct coal burning emission. Owing to the changing patterns between oxidation pathways of S(IV) in different seasons, δ34S values varied with a winter maximum (8.2 ± 1.1‰) and a summer minimum (4.9 ± 1.9‰). The results of trajectory clustering and FLEXPART demonstrated that higher concentrations of sulfate with lower sulfur isotope ratios (4.6 ± 0.8‰) were associated with air masses from the south or east, whereas lower sulfate concentrations with heavier sulfur isotope ratios (6.7 ± 1.6‰) were observed when the air masses were mainly from the north or northwest. These results suggested that the fine aerosol pollution in Beijing, especially sulfate pollution, was mainly due to coal combustion sources from regional and local regions.

This study investigates the seasonal variation, molecular distribution and stable carbon isotopic composition of diacids, oxocarboxylic acids and α -dicarbonyls to better understand the sources and formation processes of fine aerosols (PM 2.5) in Beijing. The concentrations of total dicarboxylic acids varied from 110 to 2580 ng m −3 , whereas oxoacids (9.50–353 ng m −3) and dicarbonyls (1.50–85.9 ng m −3) were less abundant. Oxalic acid was found to be the most abundant individual species, followed by succinic acid or occasionally by terephthalic acid (tPh), a plastic waste burning tracer. Ambient concentrations of phthalic acid (37.9 ± 27.3 ng m −3) and tPh (48.7 ± 51.1 ng m −3) were larger in winter than in other seasons, illustrating that fossil fuel combustion and plastic waste incineration contribute more to wintertime aerosols. The year-round mass concentration ratios of malonic acid to succinic acid (C 3 ∕ C 4) were relatively low by comparison with those in other urban aerosols and remote marine aerosols. The values were less than or equal to unity in Beijing, implying that the degree of photochemical formation of diacids in Beijing is insignificant. Moreover, strong correlation coefficients of major oxocarboxylic acids and α -dicarbonyls with nss-K + suggest that biomass burning contributes significantly to these organic acids and related precursors. The mean δ13 C value of succinic acid is the highest among all species, with values of − 17.1 ± 3.9 ‰ (winter) and − 17.1 ± 2.0 ‰ (spring), while malonic acid is more enriched in 13 C than others in autumn ( − 17.6 ± 4.6 ‰) and summer ( − 18.7 ± 4.0 ‰). The δ13 C values of major species in Beijing aerosols are generally lower than those in the western North Pacific atmosphere, the downwind region, which indicates that stable carbon isotopic compositions of diacids depend on their precursor sources in Beijing. Therefore, our study demonstrates that in addition to photochemical oxidation, high abundances of diacids, oxocarboxylic acids and α -dicarbonyls in Beijing are largely associated with anthropogenic primary emissions, such as biomass burning, fossil fuel combustion and plastic waste burning.

To understand the origins, secondary formation and seasonality of carbonaceous aerosols in North China, we collected PM2.5 samples on day- and night-time bases in summer and winter 2016 from a typical metropolis, Tianjin, and studied their carbonaceous components and stable carbon isotope ratios of total carbon (δ13CTC). PM2.5 ranged from 21.2 μg m−3 to 74.8 μg m−3 in summer and 25.3–816 μg m−3 in winter. On average, organic carbon (OC) elemental carbon (EC) and water-soluble OC were found to be higher (3–5 times) in winter than that in summer. Secondary organic carbon that estimated by EC-tracer method was enhanced by a factor of 7 in winter compared to that in summer. δ13CTC showed a small enrichment of 13C (average −25.41 ± 0.34‰) in summer compared to that (−24.42 ± 0.44‰) in winter. Linear relations and mass ratios of selected carbonaceous components and δ13CTC imply that the carbonaceous aerosols in Tianjin were mainly derived from biomass burning emissions and photochemical processing in summer. In winter, coal combustion emissions and in situ secondary formation of organics, including water-insoluble OC (WIOC), were dominant. This study warrants a need to understand the formation mechanisms of WIOC in the urban atmosphere and thus to reconcile the atmospheric models.

Fungal aerosols, which play significant roles in affecting human health and regional climate, are closely affected by rainfall. But knowledge about the influence of rainfall on fungal aerobiota in the urban atmosphere remains limited. Here, airborne total suspended particles and size-segregated particles were collected from urban Tianjin, China, to investigate such an impact by high-throughput gene sequencing. On non-rainy days, the genera Cladosporium (16.0%), Alternaria (7.9%) and Aspergillus (6.1%) dominated in fungal aerobiota. On rainy days, in addition to Cladosporium (11.1%) and Aspergillus (5.5%), the genus Schizophyllum which is apt to release spores under humid environment became more abundant (8.2%). Airborne fungi were mainly identified as plant endophytes on non-rainy days, while wood saprophytes dominated on rainy days. Precipitation had a significant impact on the fungal aerobiota in small size ranges (

Low molecular weight organic compounds are ubiquitous in the atmosphere. However, knowledge on their concentrations and molecular distribution in fresh snow remains limited. Here, twelve fresh snow samples collected at eight sites in China were investigated for dicarboxylic acids and related compounds (DCRCs) including oxocarboxylic acids and α-dicarbonyls. Dissolved organic carbon (DOC) concentrations in the snow samples ranged from 0.99 to 14.6 mg C L−1. Concentrations of total dicarboxylic acids were from 225 to 1970 μg L−1 (av. 650 μg L−1), while oxoacids (28.3–173, av. 68.1 μg L−1) and dicarbonyls (12.6–69.2, av. 31.3 μg L−1) were less abundant, accounting for 4.6–8.5% (6.2%), 0.45–1.4% (0.73%), and 0.12–0.88% (0.46%) of DOC, respectively. Molecular patterns of dicarboxylic acids are characterized by a predominance of oxalic acid (C2) (95.0–1030, av. 310 μg L−1), followed by phthalic (Ph) (9.69–244, av. 69.9 μg L−1) or succinic (C4) (23.8–163, av. 63.7 μg L−1) acid. Higher concentrations of Ph in snow from Beijing and Tianjin than other urban and rural regions suggest significant emissions from vehicular exhausts and other fossil fuel combustion sources in megacities. C2 constituted 40–54% of total diacids, corresponding to 1.5–2.6% of snow DOC. The total measured DCRCs represent 5.5–10% of snow DOC, which suggests that there are large amounts of unknown organics requiring further investigations. The spatial distributions of diacids exhibited higher loadings in megacities than rural and island sites. Molecular distributions of diacids indicated that the photochemical modification was restrained under the weak solar radiation during the snow events, while anthropogenic primary sources had a more significant influence in megacities than rural areas and islands.

Primary biological aerosol particles (PBAP) such as pollen, fungal spores, bacteria, and viruses represent a major subset of particulate matter for both coarse and fine aerosols. Although PBAP affect climate and human health, there still remains a large uncertainty regarding their sources and characteristics, especially in urban atmospheres. Here we combined online fluorescent biological aerosol particle measurements and offline fluorescent and biomarker analysis in winter in Beijing, a city suffering from severe air pollution. Our results show that the abundance of fluorescent biological particles was higher than that of many other natural environments. Bioaerosol loadings were greatly enhanced during mealtime, indicating local emissions of bioaerosols from human activities. The contributions of fungal spores to total organic carbon (OC) from fluorescent bioaerosol analyses were estimated to be around 10% both in clean and polluted periods. This study highlights the importance of human activities to emit...

Source apportionment of organic carbon (OC) and elemental carbon (EC) from PM1 (particulate matter with a diameter equal to or smaller than 1 μm) in Beijing, China was carried out using radiocarbon (14C) measurement. Despite a dominant fossil-fuel contribution to EC due to large emissions from traffic and coal combustion, nonfossil sources are dominant contributors of OC in Beijing throughout the year except during the winter. Primary emission was the most important contributor to fossil-fuel derived OC for all seasons. A clear seasonal trend was found for biomass-burning contribution to OC with the highest in autumn and spring, followed by winter and summer. 14C results were also integrated with those from positive matrix factorization (PMF) of organic aerosols from aerosol mass spectrometer (AMS) measurements during winter and spring. The results suggest that the fossil-derived primary OC was dominated by coal combustion emissions whereas secondary OC was mostly from fossil-fuel emissions. Taken together with previous 14C studies in Asia, Europe and USA, a ubiquity and dominance of nonfossil contribution to OC aerosols is identified not only in rural/background/remote regions but also in urban regions, which may be explained by cooking contributions, regional transportation or local emissions of seasonal-dependent biomass burning emission. In addition, biogenic and biomass burning derived SOA may be further enhanced by unresolved atmospheric processes.

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 (PM2.5) 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 ( µm), 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 µm) between the haze and non-haze samples, while a size shift towards large particles and large GMDs in the fine fraction ( µm) 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 µm. 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.

Aerosol proteinaceous matter is comprised of a substantial fraction of bioaerosols. Its origins and interactions in the atmosphere remain poorly understood. We present observations of total proteins, combined, and free amino acids (CAAs and FAAs) in fine particulate matter (PM2.5) samples in urban Beijing before and during the 2014 Asia-Pacific Economic Cooperation (APEC) summit. The decreases in proteins, CAAs and FAAs levels were observed after the implementation of restrictive emission controls. Significant changes were observed for the composition profiles in FAAs with the predominance of valine before the APEC and glycine during the APEC, respectively. These variations could be attributed to the influence of sources, atmospheric processes, and meteorological conditions. FAAs (especially valine and glycine) were suggested to be released by the degradation of high molecular weight proteins/polypeptides by atmospheric oxidants (i.e., ozone and free radicals) and nitrogen dioxide. Besides daytime reactions, nighttime chemistry was found to play an important role in the atmospheric formation of valine during the nights, suggesting the possible influence of NO3 radicals. Our findings provide new insights into the significant impacts of atmospheric oxidation capacity on the occurrence and transformation of aerosol proteinaceous matter which may affect its environmental, climate and health effects.

The variations in physicochemical properties of airborne particles collected during a typical transition from haze to dust were investigated using single particle analysis with transmission and scanning electron microscopes combined with online measurement of chemical compositions of airborne particles in Beijing in February 2013. The transition was divided into three phases based on the weather condition. During haze pollution (Phase 1), gaseous and particle pollutants enhanced gradually. Results from single particle analysis showed that more coatings and more anthropogenic elements (e.g., S) appeared on the surface of fine and coarse particles, which was probably caused by efficient aqueous-phase reactions under high humidity (70%) condition. Phase 2 was dust intrusion episode. PM10 reached over 1000 μg m−3. Larger fractions of mineral particles and bare-like soot particles were observed in fine particles, while the fraction of secondary particles with coatings decreased. The proportion of black carbon in submicron particles also increased. Photochemical oxidation in gas phase likely dominated in secondary formation under high O3 concentration. After the dust episode (Phase 3), secondary formation enhanced obviously. Soot aged quickly and had a larger mode of 0.45 μm than the other phases. The size modes of airborne fine particles during Phases 1 and 3 were 0.35 μm, which were a bit larger than that during Phase 2 (0.24 μm). These results indicate that dust plumes accompanied with strong wind brought mineral particles in both fine and coarse modes and freshly emitted particles with smaller sizes, and swept away pre-presence air pollutants. This study could provide detailed information on the physicochemical properties of airborne particles during typical severe pollution processes in a short time. Such short-term change should be taken into account in order to more accurately assess the environmental, climatic and health-related effects of airborne particles.

n-Alkanes and fatty acids are important molecular markers for the source apportionment of organic matter in the atmosphere. Traditional approaches to date have mostly relied upon the source-specific differences in their molecular distributions and carbon preference index. Alternatively, we demonstrate here the use of stable carbon and radiocarbon isotopic composition (δ 13C and Δ14C, respectively) of n-alkanes and n-fatty acids in aerosols from two urban receptor sites (Beijing and Tianjin) in Northeast China to assess their sources in autumn. The Δ14C n -alkanes of C19–C24 and C26–C32 even-carbon homologs (−851 to −708‰) indicate their dominance from fossil fuel combustion. In contrast, the Δ14C of most abundant palmitic acid (C16:0) and stearic acid (C18:0) suggest a larger contribution from nonfossil sources (~91%–94%), mainly due to inputs from cooking, biomass burning and microorganisms. Compared with lower Δ14C of C27 and C31 n-alkanes (−449‰), C29 n-alkane (−241‰) and C20–C30 n-fatty acids (−263‰) showed more contemporary likely due to significant contribution from plant litter and biomass burning that contain more fresh biogenic material. Fossil character of C27–C31 n-alkanes (40%) and C20–C30 n-fatty acids (30%) could be from soil resuspension and/or loess deposits in upwind regions through long-range atmospheric transport., Environmental Research Letters, 15 (7), ISSN:1748-9326, ISSN:1748-9318

Primary biological particles are an important subset of atmospheric aerosols. They have significant impacts on climate change and public health. Tianjin is a coastal megacity in the North China Plain, which is affected by both anthropogenic activities and marine air masses. To study the abundance and dynamic change of bioaerosols in Tianjin, fluorescent biological aerosol particles (FBAPs) in Tianjin were investigated by a wideband integrated bioaerosol sensor (WIBS-4A) in terms of number concentrations and size distributions in summer (11th –25th August 2018). Meanwhile, total suspended particles were collected and analyzed for chemical compounds to identify potential sources of bioaerosols. WIBS data showed that fluorescent biological particles exhibited two peaks at sunrise (~7:00) and in the evening (~20:00), which were probably caused by the enhancement of fungal spores and bacteria. Three rain events occurred during the observation period. Precipitation enhanced the abundance of biological particles, which were likely released from vegetation leaves, resuspended from soil surfaces, and/or carried by raindrops from high altitudes. The abundance of biological particles showed no significant correlation with Na+ (r = −0.17), indicating the air masses from marine areas carried limited biological particles compared to those from continental areas.

In the current AISI standard, the modified slenderness method (MSM) is proposed for the design of cold-formed steel (CFS) built-up columns. According to the available literature, such a method has been extensively adopted in hot-rolled steel research, and usually generates very conservative strength estimates. Nonetheless, there are few corresponding theoretical studies into CFS built-up columns. In this situation, this paper presents a new analytical approach to establish a computing method for the flexural buckling bearing capacity of the CFS built-up back-to-back section column. To achieve this goal, a new flexural buckling model is proposed to establish the kinematic relationship of single profiles. In addition, shear panels are employed at the location of screws to consider the discrete shear deformation restraint effect. The shear rigidity of the shear panels is determined using the cross-sectional shear stress transfer path. Then, based on the energy method, a computing method is derived. Further, simplifications are made to the formula to allow easier use in practical engineering situations. To verify the derived formula, a finite-element model (FEM) is developed and validated using the available test results. Then, based on the developed FEM, parametric studies are conducted to verify the derived formula. In addition, the performance of the derived formula is further verified by comparing the corresponding ultimate strength based on the direct strength method (DSM) expressions using available test results and FEM parametric studies. The comparison and validation results show the following: (i) the derived formula can predict the critical flexural buckling load as well as the corresponding buckling strength based on the DSM expression, and (ii) with an increase in screw spacing, the MSM will result in very conservative strength estimates for CFS built-up back-to-back section columns.

Organic molecular composition of fine aerosols in the free troposphere is poorly understood. Here, PM2.5 (particles with aerodynamic diameters ≤ 2.5 μm) samples were collected at the summit of Mt. Emei (3080 m a.s.l.) in the Southwestern China on a daytime and nighttime basis during summer 2016 (June–July). The samples were analyzed by solvent-extraction followed by derivatization and gas chromatography/mass spectrometry (GC/MS). Four classes of organic compounds, i.e. n-alkanes, fatty acids, saccharides and lignin/resin acids were measured quantitatively. Fatty acids were found to be the most abundant species with an average concentration of 401 ± 419 ng m−3 (range 25.7–1490 ng m−3) in the daytime, similar to the average concentration at night (399 ± 447 ng m−3, 19.6–1970 ng m−3). However, the concentrations of biomass burning tracers (e.g., levoglucosan), primary biological aerosol tracers (e.g., mannitol and arabitol) and low molecular weight n-alkanes derived from fossil fuel combustion in daytime samples were obviously higher than those in nighttime samples. The results suggest that valley breezes transported a large number of aerosols and their precursors from the ground surface to the summit of Mt. Emei in the daytime. Estimated with tracer-based methods, the contributions of biogenic primary sources (plant debris, fungal spore, and biomass burning) to organic carbon was in the range of 3.28–83.5% (22.0 ± 17.5%) in the daytime and 3.45–37.4% (10.9 ± 8.97%) at night. As the largest contributor, biomass burning was an important anthropogenic/natural source of aerosol particles in the free troposphere over Mt. Emei. Capsule Valley/mountain breeze is an important constraint to the temporal variations in organic aerosols over Mt. Emei.