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Aerosol hygroscopicity over the South-East Atlantic Ocean during the biomass burning season – Part 2: Influence of sea salt and burning conditions on CCN hygroscopicity

Journal Article · · Atmospheric Chemistry and Physics
 [1];  [2];  [3];  [4];  [5];  [6]
  1. Univ. of Oslo (Norway); Aarhus Univ. (Denmark); Tel Aviv Univ., Tel Aviv (Israel)
  2. Aarhus Univ. (Denmark); Tel Aviv Univ., Tel Aviv (Israel)
  3. NASA Ames Research Center (ARC), Moffett Field, Mountain View, CA (United States); Tel Aviv Univ., Tel Aviv (Israel)
  4. NASA Ames Research Center (ARC), Moffett Field, Mountain View, CA (United States)
  5. Univ. of Miami, FL (United States)
  6. Brookhaven National Laboratory (BNL), Upton, NY (United States)
+ Show Author Affiliations
Biomass burning (BB) significantly influences cloud condensation nuclei (CCN) concentrations over the southeastern Atlantic; however, aerosol hygroscopicity (κ) – a key factor for CCN activation – remains poorly constrained during the BB season. This study investigates κ variability using in situ measurements from Ascension Island during the 2016 and 2017 BB seasons. Results show substantial monthly variability, with κ values lowest in August and increasing through October. On average, κ was significantly higher in 2017 (∼ 0.55) than in 2016 (∼ 0.33), suggesting that the aerosols in 2017 were more hygroscopic and more easily activated as CCN. Sulfate and sea salt were the two dominant contributors to κ and the primary drivers of its interannual variability. During the 2017 BB season, sulfate – the major inorganic component – accounted for ∼ 34 % of the submicron aerosol mass, while sea salt, estimated via κ-closure analysis, contributed ∼ 17 %. The higher κ in 2017 was largely attributed to increased sea salt, likely driven by stronger marine winds. Approximately 67 % of sulfate was linked to BB emissions. Variations in BB combustion efficiency, modulated by regional meteorology, influenced sulfate fraction and thus κ values. Specifically, higher relative humidity and lower wind speeds over BB source regions in 2017 favored smoldering combustion, explaining the higher sulfate fraction. Overall, the observed interannual differences in aerosol hygroscopicity reflect the combined impacts of BB combustion characteristics and sea salt emissions, underscoring the critical roles of both BB and marine aerosol sources in regulating aerosol-cloud interactions over the southeastern Atlantic.
Research Organization:
Oak Ridge National Laboratory (ORNL), Oak Ridge, TN (United States). Atmospheric Radiation Measurement (ARM) Data Center
Sponsoring Organization:
USDOE Office of Science (SC), Biological and Environmental Research (BER)
Grant/Contract Number:
SC0020084; SC0021250; AC05-00OR22725; SC0012704
OSTI ID:
2589797
Alternate ID(s):
OSTI ID: 2998279
OSTI ID: 2589801
Journal Information:
Atmospheric Chemistry and Physics, Journal Name: Atmospheric Chemistry and Physics Journal Issue: 18 Vol. 25; ISSN 1680-7324
Publisher:
Copernicus GmbHCopyright Statement
Country of Publication:
United States
Language:
English

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