Preprints
https://doi.org/10.5194/acp-2021-213
https://doi.org/10.5194/acp-2021-213

  12 Apr 2021

12 Apr 2021

Review status: this preprint is currently under review for the journal ACP.

Measurement report: CCN activity and its variation with organic oxidation level and volatility observed during aerosol life cycle intensive operational period (ALC-IOP)

Fan Mei1, Jian Wang2, Shan Zhou3,a, Qi Zhang3, Sonya Collier3,b, and Jianzhong Xu3,4 Fan Mei et al.
  • 1Pacific Northwest National Laboratory, Richland, WA, 99352, USA
  • 2Washington University in St. Louis, St. Louis, MO, 63130, USA
  • 3Department of Environmental Toxicology, University of California, 1 Shields Ave., Davis, CA, 95616, USA
  • 4State Key Laboratory of Cryospheric Science, Northwest Institute of Eco-Environment and Resources, Chinese Academy of Science, Lanzhou, Gansu, 730000, China
  • acurrently at: Department of Civil and Environmental Engineering, Rice University, Houston, TX, 77005, USA
  • bcurrently at: California Air Resources Board, 1001 I Street, Sacramento, CA, USA

Abstract. Cloud condensation nuclei (CCN) spectrum and the CCN activated fraction of size selected aerosols (SR-CCN) were measured at a rural site on Long Island during the Department of Energy (DOE) Aerosol Life Cycle Intensive Operational Period (ALC-IOP) from July 15 to August 15, 2011. During the last week of the ALC-IOP, the dependence of the activated fraction on aerosol volatility was characterized by sampling downstream of a thermodenuder operated at temperatures up to 100 ⁰C. Here we present aerosol properties, including aerosol total number concentration, CCN spectrum, and the CCN hygroscopicity for air masses of representative origins during the ALC-IOP. The hygroscopicity of organic species in the aerosol is derived from CCN hygroscopicity and chemical composition. The dependence of organic hygroscopicity on the organic oxidation level (e.g., atomic O:C ratio) agrees well with theoretical predictions and results from previous laboratory and field studies. The derived κorg and O:C ratio first increase as thermal denuder (TD) temperature increases from 20 ℃ (i.e., ambient temperature) to 50 or 75 ℃, then decreases as TD temperature further increases to 100 ℃. These trends are different from previous laboratory experiments and field observations, which reported that organic O:C increased monotonically with increasing TD temperature, whereas κorg decreased with the TD temperature. The initial increases of O:C and κorg with TD temperature below 50 ℃ are likely due to the evaporation of more volatile organics with relatively lower O:C and hygroscopicity such as primary OA. Previous studies were either focused on laboratory-generated SOA or based on field observations at locations dominated by SOA.

Fan Mei et al.

Status: open (until 07 Jun 2021)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse

Fan Mei et al.

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Short summary
This work focuses on understanding aerosol's ability to act as cloud condensation nuclei (CCN) and its variations with organic oxidation level and volatility using measurements at a rural site. Aerosol properties were examined from four air mass sources. The results help improve the accurate representation of aerosol from different ambient aerosol emissions, transformation pathways, atmospheric processes in a climate model.
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