Measurement report: Large contribution of biomass burning and aqueous-phase processes to the wintertime secondary organic aerosol formation in Xi'an, Northwest China

Abstract

Abstract. Secondary organic aerosol (SOA) plays an important role in particulate air pollution, but its formation mechanism is still not fully understood. The chemical composition of non-refractory particulate matter with a diameter ≤2.5 µm (NR-PM2.5), OA sources, and SOA formation mechanisms were investigated in urban Xi'an during winter 2018. The fractional contribution of SOA to total OA mass (58 %) was larger than primary OA (POA, 42 %). Biomass-burning-influenced oxygenated OA (OOA-BB) was resolved in urban Xi'an and was formed from the photochemical oxidation and aging of biomass burning OA (BBOA). The formation of OOA-BB was more favorable on days with a larger OA fraction and higher BBOA concentration. In comparison, the aqueous-phase processed oxygenated OA (aq-OOA) was more dependent on the secondary inorganic aerosol (SIA) content and aerosol liquid water content (ALWC), and it showed a large increase (to 50 % of OA) during SIA-enhanced periods. Further van Krevelen (VK) diagram analysis suggests that the addition of carboxylic acid groups with fragmentation dominated OA aging on reference days, while the increased aq-OOA contributions during SIA-enhanced periods likely reflect OA evolution due to the addition of alcohol or peroxide groups.

Elucidating ozone and PM2.5 pollution in Fenwei Plain reveals the co-benefits of controlling precursor gas emissions in winter haze

“…The chemical composition of non-refractory particulate matter (NR-PM2.5) was measured using an AMS or an aerosol chemical speciation monitor (ACSM) at the old campus of the Institute of Earth Environment, Chinese Academy of Sciences in the 110 winter of 2013 (Zhong et al, 2020) and 2014 (Elser et al, 2016), and more recently in 2019 (Duan et al, 2022), 2020 (Duan et al, 2021), and 2021 (this study). OA factors were apportioned using the Positive Matrix Factorization (PMF) with the Multilinear Engine (ME-2) (Elser et al, 2016;Zhong et al, 2020;Duan et al, 2021;Duan et al, 2022). The 5 datasets obtained at the same sampling site were averaged to gain insights into the changes in chemical composition and OA factors over these years, although it is noted that measurements were not conducted at the same period in each year with the same duration.…”

“…To disentangle the meteorological impacts on the measured trend of PM2.5 and ozone, a machine learning (Grange et al, 2018;Dai et al, 2021;Shi et al, 2021) based meteorological normalization technique was applied, revealing the trend of de-weathered PM2.5 and ozone. Under the background of decreasing anthropogenic emissions, changes in the chemical 80 composition of PM2.5 and the organic aerosol (OA) factors were investigated based on the available studies using online aerosol mass spectrometry (Elser et al, 2016;Zhong et al, 2020;Duan et al, 2021;Duan et al, 2022). As a case study, the ozone formation potential of OVOCs was analyzed based on its reactivity (Carter, 2010), while the SOA formation potential was analyzed using a 0-D chemical box modeling (Wolfe et al, 2016) ground surface and satellite observation, in combination with the modeling results, the reduction of reactive VOCs/OVOCs 85 for the co-benefits of ozone and PM2.5 reduction are discussed.…”

Aqueous processing of water-soluble organic compounds in the eastern United States during winter

“…24,[29][30][31][32][33][34][35] Field and modeling studies demonstrate secondary OA formation in the aqueous phase from biomass burning in diverse locations that include Fresno, U.S., 36 Paris, France, 37 Douai, northern France, 38 Los Angeles, U.S., 39 the Po Valley, Italy, 40 and China. [41][42][43][44] SOA formation has been studied more intensely during summer than winter because the summertime corresponds to a peak in biogenic VOC emissions and enhanced photochemical activity in many locations. For example, SOA chamber studies utilize lower tropospheric summertime temperatures far more frequently than winter temperatures.…”

“…18 Studies of this type have been oen conducted in China, due to the severe winter haze episodes that affect air quality in many cities. [42][43][44] Signicant differences exist in the fuels used for residential heating between the U.S. and China. In the U.S., residential heating relies mainly on wood burning whereas in China, coal burning is used extensively for heating purposes.…”

“…24,29–35 Field and modeling studies demonstrate secondary OA formation in the aqueous phase from biomass burning in diverse locations that include Fresno, U.S., 36 Paris, France, 37 Douai, northern France, 38 Los Angeles, U.S., 39 the Po Valley, Italy, 40 and China. 41–44…”