21 Feb 2023
 | 21 Feb 2023

CAMx-UNIPAR Simulation of SOA Mass Formed from Multiphase Reactions of Hydrocarbons under the Central Valley Urban Atmospheres of California

Yujin Jo, Myoseon Jang, Sanghee Han, Azad Madhu, Bonyoung Koo, Yiqin Jia, Zechen Yu, Soontae Kim, and Jinsoo Park

Abstract. The UNIfied Partitioning-Aerosol phase Reaction (UNIPAR) model was established on the Comprehensive Air quality Model with extensions (CAMx) to process Secondary Organic Aerosol (SOA) formation by capturing multiphase reactions of hydrocarbons (HCs) in regional scales. SOA growth was simulated using a wide range of anthropogenic HCs including ten aromatics and linear alkanes with different carbon-lengths. The atmospheric processes of biogenic HCs (isoprene, terpenes, and sesquiterpene) were simulated for the major oxidation paths (ozone, OH radicals, and nitrate radicals) to predict day and night SOA formation. The UNIPAR model streamlined the multiphase partitioning of the lumping species originating from semi-explicitly predicted gas products and their heterogeneous chemistry to form non-volatile oligomeric species in both organic aerosol and inorganic aqueous phase. The CAMx-UNIPAR model predicted SOA formation at four ground urban sites (San Jose, Sacramento, Fresno, and Bakersfield) in California, United States during wintertime 2018. Overall, the simulated mass concentrations of the total organic matter, consisting of primary OA (POA) and SOA, showed a good agreement with the observations. The simulated SOA mass in the urban areas of California was predominated by alkane and terpene. During the daytime, low-volatile products originating from the autoxidation of long-chain alkanes considerably contributed to the SOA mass. In contrast, a significant amount of nighttime SOA was produced by the reaction of terpene with ozone or nitrate radicals. The spatial distributions of anthropogenic SOA associated with aromatic and alkane HCs were noticeably affected by the southward wind direction owing to the relatively long lifetime of their atmospheric oxidation, whereas those of biogenic SOA were nearly insensitive to wind direction. During wintertime 2018, the impact of inorganic aerosol hygroscopicity on the total SOA budget was not evident because of the small contribution of aromatic and isoprene products that are hydrophilic and reactive in the inorganic aqueous phase. However, an increased isoprene SOA mass was predicted during the wet periods, although its contribution to the total SOA was little.

Yujin Jo et al.

Status: final response (author comments only)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on egusphere-2023-93', Anonymous Referee #1, 10 May 2023
    • AC1: 'Reply on RC1', Myoseon Jang, 15 Sep 2023
  • RC2: 'Comment on egusphere-2023-93', Anonymous Referee #2, 10 Aug 2023
    • AC2: 'Reply on RC2', Myoseon Jang, 15 Sep 2023

Yujin Jo et al.


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Short summary
The CAMx-UNIPAR model simulated the SOA budget formed via multiphase reactions of hydrocarbons and the impact of emissions and climate on SOA characteristics under California’s urban environments during winter 2018. SOA growth was dominated by daytime oxidation of long-chain alkanes and nighttime terpene oxidation with O3 and NO3 radicals. The spatial distributions of anthropogenic SOA were affected by the northwesterly wind whereas those of biogenic SOA were insensitive to wind directions.