D. B. Atkinson, J. G. Radney, J. Lum, K. R. Kolesar, C. D. Cappa and Q. Zhang were supported by of the US Department of Energy (DOE) Office of Biological and Environmental Research (OBER), Atmospheric System Research (ASR) Program through Grants No. DE-SC0008937 and DE-FG02-11ER65293. A. Zelenyuk and M. S. Pekour were supported by ASR and the EMSL (Environmental Molecular Sciences Laboratory), a national scientific user facility sponsored by the DOE-OBER and located at Pacific Northwest National Laboratory.
Atmospheric Chemistry and Physics
Light -- Scattering -- Measurement, Aerosols -- Optical properties, Atmospheric aerosols
Measurements of the effect of water uptake on particulate light extinction or scattering made at two locations during the 2010 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 (GF) at 85% relative humidity and the dimensionless hygroscopicity parameter κ for oxygenated organic aerosol (OA) and for supermicron particles, 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.
Atkinson, D. B., Radney, J. G., Lum, J., Kolesar, K. R., Cziczo, D. J., Pekour, M. S., Zhang, Q., Setyan, A., Zelenyuk, A., and Cappa, C. D.: Aerosol optical hygroscopicity measurements during the 2010 CARES campaign, Atmos. Chem. Phys., 15, 4045-4061, doi:10.5194/acp-15-4045-2015, 2015.