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Title: Aerosol optical hygroscopicity measurements during the 2010 CARES campaign

Measurements of the effect of water uptake on particulate light extinction or scattering made at two locations during the 2010 Carbonaceous Aerosols and Radiative Effects Study (CARES) study around Sacramento, CA are reported. The observed influence of water uptake, characterized through the dimensionless optical hygroscopicity parameter γ, is compared with calculations constrained by observed particle size distributions and size-dependent particle composition. A closure assessment has been carried out that allowed for determination of the average hygroscopic growth factors (GFs) at 85% relative humidity and the dimensionless hygroscopicity parameter κ for oxygenated organic aerosol (OA) and for supermicron particles (defined here as particles with aerodynamic diameters between 1 and 2.5 microns), yielding κ = 0.1–0.15 and 0.9–1.0, respectively. The derived range of oxygenated OA κ values are in line with previous observations. The relatively large values for supermicron particles is consistent with substantial contributions of sea-salt-containing particles in this size range. Analysis of time-dependent variations in the supermicron particle hygroscopicity suggest that atmospheric processing, specifically chloride displacement by nitrate and the accumulation of secondary organics on supermicron particles, can lead to substantial depression of the observed GF.
Authors:
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Publication Date:
OSTI Identifier:
1197807
Grant/Contract Number:
SC0008937; FG02-11ER65293
Type:
Published Article
Journal Name:
Atmospheric Chemistry and Physics (Online)
Additional Journal Information:
Journal Name: Atmospheric Chemistry and Physics (Online); Journal Volume: 15; Journal Issue: 8; Journal ID: ISSN 1680-7324
Publisher:
European Geosciences Union
Sponsoring Org:
USDOE Office of Science (SC), Biological and Environmental Research (BER) (SC-23)
Country of Publication:
Germany
Language:
English