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Rethinking of Black-Carbon Associated Organic Particles: Insights into Aged Biomass Burning Organic Aerosol
JUNFENG WANG, Jianhuai Ye, Dantong Liu, Yangzhou Wu, Jian Zhao, Weiqi Xu, Conghui Xie, Fuzhen Shen, Jie Zhang, Paul Ohno, Yiming Qin, Scot T. Martin, Alex Lee, Pingqing Fu, Daniel Jacob, Qi Zhang, Yele Sun, Mindong Chen, Xinlei Ge, Xiuyong Zhao, Harvard University
Abstract Number: 56
Working Group: Aerosols, Clouds and Climate
Abstract
Black carbon (BC) particles in Beijing summer haze pollution play an important role in the regional radiation balance and related environmental processes, yet understanding the factors that lead to variability in those effects remains limited. The role of BC particles can vary with the aerosol mixing state (i.e., internally compared to externally mixed) as well as with other chemical species that can coat the BC cores. Here, we present observations by a soot-particle aerosol mass spectrometer of BC-containing submicron particulate matter (BC-PM1) in the summer of 2017 in Beijing, China. These observations were compared to concurrently measured total non-refractory submicron particulate matter (NR-PM1) by a high-resolution aerosol mass spectrometer (HR-AMS). There were important differences between NR-PM1 and BC-PM1 related to organic aerosol (OA) composition. Hydrocarbon-like OA (HOA) in BC-PM1 was up to two-fold higher than that in NR-PM1 in fresh plumes of vehicle emissions, indicating that a part of HOA in BC-PM1 may be undetectable by HR-AMS. The implication is that the factorization analysis for the bulk NR-PM1 may be misinterpreted. Cooking-related OA was only identified in NR-PM1, while aged biomass burning OA (A-BBOA) was a unique factor only identified in BC-PM1. The A-BBOA was linked to those heavily coated BC characterized by coating-to-BC mass ratios RBC > 9 and particle mode size > 300 nm. These particles may lead to enhancement of the light absorption ability of BC by a factor of two via the “lensing effect”. Furthermore, the fractions of less-oxidized oxygenated OA (LO-OOA) were similar in both types of particles. More-oxidized oxygenated OA (MO-OOA) identified in BC-PM1 was found to be slightly different from that observed by HR-AMS, mainly due to the influences of A-BBOA. Overall, these findings highlight that a unique biomass-burning related OA associated with BC may be ubiquitous in transported BC-PM1, and this OA may play a role in regional energy balance that has not previously been fully considered.