Search

Biomass burning serves as important sources of volatile organic compounds (VOCs), yet our understanding of the molecular characteristics of oxygenated volatile organic compounds (OVOCs) from fresh emissions remains limited. In this study, gaseous organic compounds in fresh smokes from burning typical Chinese crop straws and woods are measured using an iodide time‐of‐flight chemical ionization mass spectrometer. Approximately 750 molecular formulas are identified, with CHO compounds containing carbon, hydrogen and oxygen atoms accounting for 77%–95% of the total. C1–C3 organic acids and dicarboxylic acids dominate the total CHO signal intensities by 27%–48%, while well‐known molecular markers of biomass burning, such as monosaccharide, guaiacol and syringol derivatives, contribute 7%–17%. Notably, crop straw and wood burning emit a higher abundance of guaiacol than syringol derivatives by a factor of 5. Additionally, a variety of nitrogen‐containing compounds (mainly in the CHON group) is identified, including isocyanate, amide, amino acids, and pyridine. The mass spectral profiles of organic compounds are largely similar between crop straw and wood burning fuels, although wood burning produces higher contributions of compounds with carbon atoms numbers >10. The saturation concentrations of organic compounds are estimated using molecular formula‐based volatility parameterization, revealing that semi‐volatile and intermediate VOCs (S/intermediate volatility organic compounds (IVOCs)) predominate smoke releases by 35%–60% and 20%–43%, respectively, with only a small fraction of low‐volatility compounds. Given the widespread nature of biomass burning in winter China, our results may have significant implications for interpreting secondary organic aerosol formation through gas‐particle partitioning or aqueous‐phase reactions. Plain Language Summary: Biomass burning is a significant source of volatile organic compounds (VOCs), with oxygenated volatile organic compounds (OVOCs) being particularly important due to their high reactivity and their contribution to the radical budget and secondary products formation. However, previous research has primarily focused on a limited number of OVOCs species from pine, spruce, and other biofuels, leading to insufficient studies on the full mass spectra of OVOCs from biomass smokes. Our study has addressed this gap by identifying approximately 750 OVOCs from burning typical Chinese crop straws and woods. We found that C1–C3 organic acids and dicarboxylic acids are the predominant contributors to total signal intensities. This expands on previous studies that have focused on a limited well‐known molecular markers of biomass burning, such as monosaccharide, guaiacol and syringol derivatives, and reveals the presence of nitrogen‐containing compounds, including isocyanate, amide, amino acids, and pyridine. The saturation concentrations of organic compounds are estimated, highlighting the importance of semi‐volatile and intermediate VOCs (S/IVOCs) in fresh smoke releases. Our study contributes to a better understanding of complex chemistry of biomass burning and its impact on air quality. It will serve as a crucial basis for accurately assessing biomass burning related‐secondary organic aerosol formation. Key Points: C1–C3 organic acids and dicarboxylic acids dominate the total signal intensities of fresh crop straw and wood burning emissionsThe mass spectral profiles are largely similar across different fuels, with wood burning produces higher contributions of large compoundsSemi‐volatile and intermediate volatile organic compounds predominate fresh smoke emissions, with only a small fraction of low‐volatility compounds [ABSTRACT FROM AUTHOR]

Photochemical aging is a key atmospheric processing, yet the changes in physicochemical properties of organic aerosol (OA) during photochemical aging of primary emissions from cooking and burning are less understood. Here we conducted 12 burning (straw, wood, and coal) and cooking experiments to characterize the evolution of size distributions, volatility, and glass transition temperature (Tg) from fresh smoke to aged OA with an equivalent photochemical age of ∼1.5 days using an oxidation flow reactor‐thermodenuder‐aerosol mass spectrometer system. The mass spectra of OA showed significant changes during photochemical aging, for example, the rapid degradation of m/z 60 for straw and wood burning OA, and the large increase in f44 (fraction of m/z 44 in OA) for all OA. The contributions of non‐volatile compounds to the total OA in aged burning OA (1.6%–5.3%) decreased considerably compared with those in fresh burning smoke (2.3%–17.1%), suggesting that photochemical aging of primary emissions for ∼1.5 days produced more volatile secondary OA (SOA). Consistently, the pronounced formation of SOA below 150 nm was observed, and it showed more volatile properties than aged large particles. The Tg of OA under dry conditions (Tg,org) was estimated based on volatility distributions, and the results showed increased Tg,org during photochemical aging of biomass burning and coal combustion emissions, while decreased Tg,org for aged cooking OA. Overall, our results illustrate the different changes in size distributions, volatility, and Tg,org through photochemical aging of different primary emissions, which in turn affect their impacts on radiative forcing and human health. Plain Language Summary: The properties of organic aerosol (OA) from primary emissions can have rapid changes during photochemical aging, and hence affect the radiative forcing and health effects of OA. However, changes in physicochemical properties of OA during aging, for example, size distributions, volatility, and glass transition temperature (Tg), are less understood, particularly for the OA from different types of primary emissions. In this work, we characterized such changes in size distributions, volatility, and viscosity of OA from biomass burning, coal combustion, and cooking emissions during photochemical aging. We observed pronounced formation of secondary OA (SOA) below 150 nm after aging, which showed higher volatility than the aged larger OA particles. The aged biomass burning and coal combustion emissions showed lower volatilities and higher viscosities than fresh emissions. Our results demonstrate that the size distributions, volatility, and viscosity of OA in regions with high anthropogenic emissions can have significant changes in days and hence exert different climate and health effects. Key Points: The volatility and glass transition temperature of organic aerosol (OA) from primary emissions changed significantly during photochemical agingSecondary OA formed below 150 nm was more volatile than aged large particlesThe aged biomass burning and coal combustion emissions showed lower volatilities and higher viscosities than fresh emissions [ABSTRACT FROM AUTHOR]

Water-soluble and water-insoluble organic aerosol (WSOA and WIOA) constitute a large fraction of fine particles in winter in northern China, yet our understanding of their sources and processes are still limited. Here we have a comprehensive characterization of WSOA in cold season in Beijing. Particularly, we present the first mass spectral characterization of WIOA by integrating online and offline organic aerosol measurements from high-resolution aerosol mass spectrometer. Our results showed that WSOA on average accounted for 59 % of the total OA and comprised dominantly secondary OA (SOA, 69 %). The WSOA composition showed significant changes during the transition season from autumn to winter. While the photochemical-related SOA dominated WSOA (51 %) in early November, the oxidized SOA from biomass burning increased substantially from 8 % to 29 % during the heating season. Comparatively, local primary OA dominantly from cooking aerosol contributed the major fraction of WSOA during clean periods. WIOA showed largely different spectral patterns from WSOA which were characterized by prominent hydrocarbon ions series and low oxygen-to-carbon (O/C = 0.19) and organic mass-to-organic carbon (OM/OC = 1.39) ratios. The nighttime WIOA showed less oxidized properties (O/C = 0.16 vs. 0.24) with more pronounced polycyclic aromatic hydrocarbons (PAHs) signals than daytime, indicating the impacts of enhanced coal combustion emissions on WIOA. The evolution process of WSOA and WIOA was further demonstrated by the triangle plot of f44 (fraction of m/z 44 in OA) vs. f43 , f44 vs. f60 , and the Van Krevelen diagram (H/C vs. O/C). We also found more oxidized WSOA and an increased contribution of SOA in WSOA compared with previous winter studies in Beijing, indicating that the changes in OA composition due to clean air act have affected the sources and properties of WSOA. [ABSTRACT FROM AUTHOR]

Large reductions in anthropogenic emissions during the Chinese New Year (CNY) holiday in Beijing have been well reported. However, the changes during the CNY of 2021 are different because most people stayed in Beijing to control the spread of coronavirus disease (COVID-19). Here a high-resolution aerosol mass spectrometer (HR-AMS) was deployed for characterization of the changes in size-resolved aerosol composition and sources during the CNY. We found that the reductions in traffic-related NO x and fossil fuel-related organic aerosol (OA), and cooking OA (1.3–12.7%) during the CNY of 2021 were much smaller than those in previous CNY holidays of 2013, 2015, and 2020. In contrast, the mass concentrations of secondary aerosol species except nitrate showed ubiquitous increases (17.6–30.4%) during the CNY of 2021 mainly due to a 4-day severe haze episode. OA composition also changed substantially during the CNY of 2021. In particular, we observed a large increase by nearly a factor of 2 in oxidized primary OA likely from biomass burning, and a decrease of 50.1% in aqueous-phase secondary OA. A further analysis of the severe haze episode during the CNY illustrated a rapid transition of secondary formation from photochemical to aqueous-phase processing followed by a scavenging process, leading to significant changes in aerosol composition, size distributions, and oxidation degree of OA. A parameterization relationship between oxygen-to-carbon (O/C) and f 44 (fraction of m/z 44 in OA) from a collocated capture vaporizer aerosol chemical speciation monitor (CV-ACSM) was developed, which has a significant implication for characterization of OA evolution and the impacts on hygroscopicity due to the rapidly increased deployments of CV-ACSM worldwide. [Display omitted] • Secondary species except NO 3 increased during the controlled Chinese New Year (CNY). • Traffic and cooking organic aerosol had small changes during the controlled CNY. • A new parameterization between O/C and f 44 for CV-ToF-ACSM was developed. [ABSTRACT FROM AUTHOR]

Air quality has been improved significantly from 2017 to 2020 in Fenhe Plain, one of the most polluted regions in China. However, severe haze episodes from days to weeks were still frequently observed in cold seasons, and the sources and formation mechanisms especially organic aerosols are poorly understood due to the limited highly time-resolved measurements. Here we have a comprehensive characterization of chemical composition, variations and sources of fine particles in fall and winter in Fenhe Plain mainly using a PM 2.5 Aerosol Chemical Speciation Monitor. Our results showed that organics and nitrate were two major species of PM 2.5 , on average accounting for 35.4% and 27.0%, respectively, and they played consistently important roles across different pollution levels. Positive matrix factorization revealed three primary sources from traffic, biomass burning and coal combustion emissions, and two secondary factors that are associated with photochemical and aqueous-phase processing. While secondary OA (SOA) dominated OA for the entire study (63%), large increases in primary OA from 19% to 41% were observed during heating period. Particularly, we found a high contribution of photochemical OOA (45%) during severely polluted periods in heating season demonstrating the presence of strong photochemical production in winter. Most aerosol species presented similarly pronounced diurnal cycles with low concentrations during daytime indicating the major influences from planetary boundary layer and primary emissions. The bivariate polar plots further illustrated the different sources of primary and secondary species, i.e., local emissions versus regional transport from the south and southeast. By analyzing four case studies, we found three major formation mechanisms of severe haze episodes that were driven by photochemical processing, aqueous-phase production, and local emissions, respectively. Therefore, different mitigating strategies are suggested in Fenhe Plain depending on the types of severe haze episodes. [Display omitted] • Organics and nitrate dominated particle composition in cold season in Fenhe plain. • POA were mainly from coal combustion, biomass burning, and traffic emissions. • Strong photochemical production of SOA was observed during winter severe pollution. [ABSTRACT FROM AUTHOR]

Secondary organic aerosols (SOA) constitute a large fraction of atmospheric aerosols, yet our knowledge of the formation and aging processes of SOA in megacities of China is still limited. In this work, the formation and aging processes of SOA in winter in Beijing was investigated using a high-resolution aerosol mass spectrometer (AMS) and an oxidation flow reactor (OFR). Our results showed that the OA enhancement from OH aging peaked at ∼3.9 equivalent days with an average enhancement of 0.9 (±0.3) μg m−3. Positive matrix factorization analysis of AMS-OFR data identified three primary OA (POA) and two SOA factors. While the concentrations of POA factors decreased as a function of photochemical age, the two SOA factors showed clear enhancements by 2.5 and 4.3 μg m−3 at ∼3.9 and ∼2.6 days of equivalent photochemical age, respectively. The average contribution of SOA to the total OA was 47% in ambient air and 87% in OFR-oxidized ambient air. The elevated oxygen-to-carbon (O/C) ratio from 0.49 to 0.77–0.82 and the decreased hydrogen-to-carbon (H/C) from 1.37 to ∼1.1 highlighted the formation of more oxidized SOA during photochemical aging in winter in Beijing. The ubiquitous SOA enhancement as a function of OA levels indicated the significant formation potential of SOA in winter, and it varied differently among different episodes. In particular, we observed a maximum SOA enhancement of 38.6 μg m−3 during a biomass burning event. This result demonstrates that photochemical oxidation of ubiquitous biomass burning emissions can be a large source of SOA in winter in North China Plain. • The decreased POA and enhanced SOA concentrations after aging are observed. • Elevated O/C highlights the formation of more oxidized SOA during photochemical aging. • Photochemical oxidation of biomass burning emissions can be a large source of SOA. [ABSTRACT FROM AUTHOR]