Photoacoustic optical properties at UV, VIS, and near IR wavelengths for laboratory generated and winter time ambient urban aerosols 1Physics Department, University of Nevada, Reno, Nevada System of Higher Education, 1664 N. Virginia Street, Reno, NV, 89557, USA
08 Mar 2012
2Atmospheric Sciences and Global Change Division, Pacific Northwest National Laboratory, Richland, WA, 99352, USA
3Desert Research Institute, Nevada System of Higher Education, 2215 Raggio Parkway, Reno, NV, 89512, USA
4NASA Goddard Institute for Space Studies, 2880 Broadway, New York, NY 10025, USA
Received: 26 Aug 2011 – Published in Atmos. Chem. Phys. Discuss.: 08 Sep 2011 Abstract. We present the laboratory and ambient photoacoustic (PA) measurement of
aerosol light absorption coefficients at ultraviolet wavelength (i.e., 355 nm)
and compare with measurements at 405, 532, 870, and 1047 nm.
Simultaneous measurements of aerosol light scattering coefficients were
achieved by the integrating reciprocal nephelometer within the PA's acoustic
resonator. Absorption and scattering measurements were carried out for
various laboratory-generated aerosols, including salt, incense, and kerosene
soot to evaluate the instrument calibration and gain insight on the spectral
dependence of aerosol light absorption and scattering. Ambient measurements
were obtained in Reno, Nevada, between 18 December 2009 and 18 January 2010.
The measurement period included days with and without strong ground level
temperature inversions, corresponding to highly polluted (freshly emitted
aerosols) and relatively clean (aged aerosols) conditions. Particulate
matter (PM) concentrations were measured and analyzed with other tracers of
traffic emissions. The temperature inversion episodes caused very high
concentration of PM2.5 and PM10 (particulate matter with
aerodynamic diameters less than 2.5 μm and 10 μm, respectively)
and gaseous pollutants: carbon monoxide (CO), nitric oxide (NO), and
nitrogen dioxide (NO2). The diurnal change of absorption and scattering
coefficients during the polluted (inversion) days increased approximately by
a factor of two for all wavelengths compared to the clean days. The spectral
variation in aerosol absorption coefficients indicated a significant amount
of absorbing aerosol from traffic emissions and residential wood burning.
The analysis of single scattering albedo (SSA), Ångström exponent of
absorption (AEA), and Ångström exponent of scattering (AES) for
clean and polluted days provides evidences that the aerosol aging and
coating process is suppressed by strong temperature inversion under cloudy
conditions. In general, measured UV absorption coefficients were found to be
much larger for biomass burning aerosol than for typical ambient aerosols.
Revised: 21 Feb 2012 – Accepted: 24 Feb 2012 – Published: 08 Mar 2012
Citation: Gyawali, M., Arnott, W. P., Zaveri, R. A., Song, C., Moosmüller, H., Liu, L., Mishchenko, M. I., Chen, L.-W. A., Green, M. C., Watson, J. G., and Chow, J. C.: Photoacoustic optical properties at UV, VIS, and near IR wavelengths for laboratory generated and winter time ambient urban aerosols, Atmos. Chem. Phys., 12, 2587-2601, doi:10.5194/acp-12-2587-2012, 2012.