Droplet activation properties of organic aerosols observed at an urban site during CalNex-LA
- Brookhaven National Laboratory, Upton New York USA; Pacific Northwest National Laboratory, Richland Washington USA
- Cooperative Institute for Research in Environmental Sciences, Boulder Colorado USA; Department of Chemistry and Biochemistry, University of Colorado, Boulder Colorado USA
- School of Earth, Atmospheric and Environmental Sciences, University of Manchester, Manchester UK
- School of Earth, Atmospheric and Environmental Sciences, University of Manchester, Manchester UK; National Centre for Atmospheric Science, University of Manchester, Manchester UK
- NOAA Earth System Research Laboratory, Boulder Colorado USA
- Brookhaven National Laboratory, Upton New York USA
Size-resolved cloud condensation nuclei (CCN) spectra and aerosol chemical composition were characterized at an urban supersite in Pasadena, California, from 15 May to 4 June 2010, during the CalNex campaign. The derived hygroscopicity (κCCN) of CCN-active particles with diameter between 97 and 165 nm ranged from 0.05 to 0.4. Diurnal variation showed a slight decrease of κCCN from 8:00 to 16:00 (from 0.24 to 0.20), which is attributed to increasing organics volume fraction resulted from secondary organic aerosol (SOA) formation. The derived hygroscopicity distribution and maximum activated fraction of the size selected particles were examined as functions of photochemical age. The result indicates that condensation of secondary species (e.g., SOA and sulfate) quickly converted hydrophobic particles to hydrophilic ones, and during daytime, nearly every particle became a CCN at ~0.4% in just a few hours. Based on κCCN and aerosol chemical composition, the organic hygroscopicity (κorg) was derived, and ranged from 0.05 to 0.23 with an average value of 0.13, consistent with the results from earlier studies. The derived κorg generally increased with the organic oxidation level, and most of the variation in κorg could be explained by the variation of the organic O : C atomic ratio alone. The least squares fit of the data yielded κorg = (0.83 ± 0.06) × (O:C) + (-0.19 ± 0.02). Compared to previous results based on CCN measurements of laboratory generated aerosols, κorg derived from measurements during the CalNex campaign exhibited stronger increase with O : C atomic ratio and therefore substantially higher values for organics with average O : C greater than 0.5.
- Research Organization:
- Pacific Northwest National Lab. (PNNL), Richland, WA (United States)
- Sponsoring Organization:
- USDOE
- DOE Contract Number:
- AC05-76RL01830
- OSTI ID:
- 1088622
- Report Number(s):
- PNNL-SA-93766; KP1704010
- Journal Information:
- Journal of Geophysical Research: Atmospheres, Vol. 118, Issue 7; ISSN 2169-897X
- Publisher:
- American Geophysical Union
- Country of Publication:
- United States
- Language:
- English
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