Measurements of Optical Properties of Secondary Organic Aerosol Using Photoacoustic Instrumentation

Chen Song (1), Madhu Gyawali (2), Rahul A. Zaveri (1), John Shilling (1), and W. Patrick Arnott (2)

(1) Pacific Northwest National Laboratory, Richland, WA (2) University of Nevada, Reno, NV

     Abstract Number: 724
     Last modified: May 14, 2010

Abstract
It is well known that light absorption by dust and black carbon aerosols (soot) has a warming effect on climate while scattering by sulfate, nitrate, and sea salt aerosols has a cooling effect. However, there are large uncertainties associated with light absorption and scattering by different types of organic aerosols, especially in the near-UV and UV.

Here, we present preliminary results from a recent laboratory study focused on measuring optical properties of secondary organic aerosols (SOA) formed from ozonolysis of a-pinene in the presence of acidic sulfate aerosol and NO3 radicals - conditions typically found in power plant plumes at night [Zaveri et al., 2010]. Aerosol light absorption and scattering were measured using photoacoustic instruments at four wavelengths: 355, 405, 532 and 870 nm.

Pronounced light absorption at 355 and 405 nm was observed for SOA formed from oxidation of a-pinene and nitrate radical (NO3) in the presence of strongly acidic seed aerosol at low RH (~2%). No light absorption was observed when RH was higher than 12%, or in the presence of weak and neutral inorganic seed aerosols, or when only ozone was used as an oxidant. Our results also indicate that a-pinene can react with strongly acidic seed aerosols and enhance light absorption, possibly by forming oligomeric species. Further analysis is needed to assess the implications of these findings.

Reference:
Zaveri, R.A., C.M. Berkowitz, F.J. Brechtel, M.K. Gilles, J.M. Hubbe, J.T. Jayne, L.I. Kleinman, A. Laskin, S. Madronich, T.B. Onasch, M. Pekour, S.R. Springston, J.A. Thornton, A.V. Tivanski, and D.R. Worsnop (2010), Nighttime chemical evolution of aerosol and trace gases in a power plant plume: Implications for secondary organic nitrate and organosulfate aerosol formation, NO3 radical chemistry, and N2O5 heterogeneous hydrolysis, J. Geophysical Research, doi:10.1029/2009JD013250, in press.