Preprints
https://doi.org/10.5194/egusphere-2023-1818
https://doi.org/10.5194/egusphere-2023-1818
23 Aug 2023
 | 23 Aug 2023

Source Apportionment of Soot Particles and Aqueous-Phase Processing of Black Carbon Coatings in an Urban Environment

Ryan N. Farley, Sonya Collier, Christopher D. Cappa, Leah R. Williams, Timothy B. Onasch, Lynn M. Russell, Hwajin Kim, and Qi Zhang

Abstract. The impacts of soot particles on climate and human health depend on the concentration of black carbon (BC) as well as the thickness and composition of the coating material, i.e., organic and inorganic compounds internally mixed with BC. In this study, the size-resolved chemical composition of BC-containing aerosol was measured using a high-resolution soot-particle aerosol mass spectrometer (SP-AMS) during wintertime in Fresno, California, a location influenced by abundant combustion emissions and frequent fog events. Concurrently, particle optical properties were measured to investigate the BC absorption enhancement. Positive matrix factorization (PMF) analysis was performed on the SP-AMS mass spectral measurements to explore the sources of soot particles and the atmospheric processes affecting the properties of BC coatings. The analysis revealed that residential wood burning and traffic are the dominant sources of soot particles. Alongside primary soot particles originating from biomass burning (BBOABC) and vehicles (HOABC) two distinct types of processed BC-containing aerosol were identified: fog-related oxidized organic aerosol (FOOABC) and winter-background OOABC (WOOABC). Both types of OOABC showed evidence of having undergone aqueous processing, albeit with differences. The concentration of FOOABC was substantially elevated during fog events, indicating the formation of aqueous secondary organic aerosol (aqSOA) within fog droplets. On the other hand, WOOABC was present at a relatively consistent concentration throughout the winter and is likely related to the formation of secondary organic aerosol (SOA) in both the gas phase and aerosol liquid water. By comparing the chemical properties and temporal variations of FOOABC and WOOABC, we gain insights into the key aging processes of BC aerosol. It was found that aqueous-phase reactions facilitated by fog droplets had a significant impact on the thickness and chemical composition of BC coatings, thereby affecting the light absorption and hygroscopic properties of soot particles. These findings underscore the important role of chemical reactions occurring within clouds and fogs and influencing the climate forcing of BC aerosol in the atmosphere.

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Journal article(s) based on this preprint

07 Dec 2023
Source apportionment of soot particles and aqueous-phase processing of black carbon coatings in an urban environment
Ryan N. Farley, Sonya Collier, Christopher D. Cappa, Leah R. Williams, Timothy B. Onasch, Lynn M. Russell, Hwajin Kim, and Qi Zhang
Atmos. Chem. Phys., 23, 15039–15056, https://doi.org/10.5194/acp-23-15039-2023,https://doi.org/10.5194/acp-23-15039-2023, 2023
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The requested preprint has a corresponding peer-reviewed final revised paper. You are encouraged to refer to the final revised version.

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Soot particles, also known as black carbon (BC), have important implication on global climate...
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