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JOURNAL OF GEOPHYSICAL RESEARCH,
VOL. 110,
D18209,
doi:10.1029/2004JD005624,
2005
Observations of smoke-influenced aerosol during the Yosemite Aerosol Characterization Study: 2. Aerosol scattering and absorbing
properties
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
J. L. Collett
Department of Atmospheric Science, Colorado State University, Fort Collins, Colorado, USA
D. E. Day
Cooperative Institute for Research in the Atmosphere (CIRA), Colorado State University, Fort Collins, Colorado, USA
W. C. Malm
Cooperative Institute for Research in the Atmosphere (CIRA), Colorado State University, Fort Collins, Colorado, USA
Abstract
Direct observations and size-distribution-based estimates of light-scattering coefficients (b
sp
) are presented for the Yosemite Aerosol Characterization Study (YACS), which took place during the summer of 2002, an active
fire year. Uncertainty in the estimates of b
sp
were found to be sensitive to the choice of the aerosol refractive indices, which were retrieved by aligning optical particle
counter measurements to differential mobility analyzer observations and, in addition, were calculated from composition measurements.
Aerosol composition during the study was dominated by organic carbon, with highest levels observed during periods impacted
by biomass burning smoke influenced hazes. As a result, estimates of the aerosol refractive index from composition measurements
were highly sensitive to the assumed properties of organic carbon. Retrieved and calculated refractive indices were in agreement
for reasonable assumptions for properties of organic carbon. Excellent agreement (within 6%) was found between measured b
sp
and size-distribution derived b
sp
if the imaginary component of the refractive index, determined from composition measurements and assuming all species were
internally mixed, was included in the Mie calculation. Under the internally mixed assumption, aerosols sampled during the
study were modeled as weakly absorbing, with computed dry single scattering albedo ranging from 0.86 to 0.94. Calculated light
absorption coefficients yielded a study-averaged dry aerosol mass absorption efficiency of 0.37 ± 0.05 m2g−1.
Received 22
November
2004;
accepted 6
June
2005;
published 28
September
2005.
Keywords: smoke;
visibility;
aerosols.
Index Terms: 0305 Atmospheric Composition and Structure: Aerosols and particles (0345, 4801, 4906); 0345 Atmospheric Composition and Structure: Pollution: urban and regional (0305, 0478, 4251); 0360 Atmospheric Composition and Structure: Radiation: transmission and scattering; 9350 Geographic Location: North America.
Read Full Article (file size: 850296 bytes) Cited by
Citation: McMeeking, G. R., S. M. Kreidenweis, C. M. Carrico, J. L. Collett, D. E. Day, and W. C. Malm
(2005),
Observations of smoke-influenced aerosol during the Yosemite Aerosol Characterization Study: 2. Aerosol scattering and absorbing
properties,
J. Geophys. Res.,
110,
D18209,
doi:10.1029/2004JD005624.
Copyright 2005 by the American Geophysical Union.
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