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JOURNAL OF GEOPHYSICAL RESEARCH, VOL. 110, D09206, doi:10.1029/2004JD005389, 2005

Observations of smoke-influenced aerosol during the Yosemite Aerosol Characterization Study: Size distributions and chemical composition

G. R. McMeeking

Department of Atmospheric Science, Colorado State University, Fort Collins, Colorado, USA


S. M. Kreidenweis

Department of Atmospheric Science, Colorado State University, Fort Collins, Colorado, USA


C. M. Carrico

Department of Atmospheric Science, Colorado State University, Fort Collins, Colorado, USA


T. Lee

Department of Atmospheric Science, Colorado State University, Fort Collins, Colorado, USA


J. L. Collett Jr.

Department of Atmospheric Science, Colorado State University, Fort Collins, Colorado, USA


W. C. Malm

Cooperative Institute for Research in the Atmosphere, Colorado State University, Fort Collins, Colorado, USA


Abstract

The Yosemite Aerosol Characterization Study (YACS) took place in Yosemite National Park from 15 July to 5 September 2002, during which time air masses arriving at the site were believed to have been influenced by smoke from numerous wildfires active in the western United States. Physical, optical, and chemical aerosol measurements were made to characterize visibility and to help define aerosol sources contributing to haze in the park, with a particular emphasis on the role of prescribed and wild fires. Measurements of dry aerosol size distributions were made with a differential mobility analyzer (DMA) and an optical particle counter (OPC). An iterative alignment method assuming a range of refractive indices was applied to OPC size distributions to match them to DMA size distributions, returning the real refractive index that yielded the best fit and generating a complete size distribution for 0.04 < D p < 2 μm. Retrieved dry aerosol real refractive indices generally ranged from 1.56 to 1.59 and were comparable to values estimated from composition measurements. Organic carbon was the dominant aerosol species during the study, particularly during periods identified as smoke impacted. Mie theory was used to determine mass scattering efficiencies (λ = 530 nm) from measured dry size distributions using retrieved refractive indices. These ranged from 3 to 6 m2 g−1, with the highest values occurring during smoke-impacted episodes.

Received 25 August 2004; accepted 25 February 2005; published 11 May 2005.

Keywords: smoke; visibility; aerosols.

Index Terms: 0305 Atmospheric Composition and Structure: Aerosols and particles (0345, 4801, 4906); 0315 Atmospheric Composition and Structure: Biosphere/atmosphere interactions (0426, 1610); 0345 Atmospheric Composition and Structure: Pollution: urban and regional (0305, 0478, 4251); 0360 Atmospheric Composition and Structure: Radiation: transmission and scattering.

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Citation: McMeeking, G. R., S. M. Kreidenweis, C. M. Carrico, T. Lee, J. L. Collett Jr., and W. C. Malm (2005), Observations of smoke-influenced aerosol during the Yosemite Aerosol Characterization Study: Size distributions and chemical composition, J. Geophys. Res., 110, D09206, doi:10.1029/2004JD005389.