The formation and evolution of secondary organic aerosol during summer in Xi'an: Aqueous phase processing in fog-rain days

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

“…1 and Table S1). This average concentration was higher 150 than that measured in the summer of 2019 in Xi'an (22.3 μg m -3 , Duan et al, 2021), due to the increase of source emissions in winter than in summer which was also observed in other cities (Sun et al, 2015;Xu et al, 2014Xu et al, , 2016. Meanwhile, the average NR-PM2.5 concentration observed in our study was much lower than those observed in the winter of 2013 in Xi'an (140.0 μg m -3 during reference days and 537.0 μg m -3 during haze days, respectively) (Elser et al, 2016), pointing to an improved air quality.…”

“…The winter campaign was conducted from 4 th December 2018 to 15 th March 2019 at the campus of the 85 Institute of Earth Environment, Chinese Academy of Sciences (34°23′N, 108°89′, 12 m above the ground level) in downtown Xi'an with surrounding residential, commercial, and traffic areas (Duan et al, 2021).…”

“…A SP-LToF-AMS (Aerodyne Research Inc.) was deployed for the online characterization of PM2.5 with a time resolution of 1 min. The detailed instrument description could be found in Onasch et al (2012) 90 and a similar operation was conducted as that in Duan et al (2021). The contribution of black carbon (BC) was not considered, and only NR-PM2.5 composition, including organics (OA), nitrate (NO3 -), sulfate (SO4 2-), ammonium (NH4 + ), and chloride (Cl -) were analyzed.…”

“…The elemental ratios including oxygen-to-carbon (O/C), organic mass-toorganic carbon (OM/OC) and hydrogen-to-carbon (H/C) were also analyzed for the high-resolution OA mass spectra based on the Improved Ambient (I-A) method (Canagaratna et al, 2015). Meanwhile, the data and error matrices of high-resolution OA mass spectra for m/z 12-120 were preprocessed, and OA source apportionment was performed using Positive Matrix Factorization (PMF) and multilinear engine 115 (Paatero, 1999), as conducted in Duan et al (2021).…”

“…Chemical composition and OA sources were analyzed and compared with those resolved in Elser et al (2016), in order to elucidate the aerosol variation in recent years due to emission controls. Meanwhile, the SOA formation mechanisms and its 80 contribution to haze event were investigated and compared with those in the summer of 2019 (Duan et al, 2021).…”