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Colloquium

Department of Atmospheric Science

Tues., Mar. 7, 3:10 pm, EN6085

In-Site Measurements of Water Uptake by Black Carbon-Containing Aerosol in Wildfire Plumes

Dr. Anne Perring

National Oceanic and Atmospheric Administration

Abstract

Water uptake by black carbon (BC)-containing aerosol is quantified in North American wildfire plumes of varying age (1 to ~40 hours old) sampled during the SEAC4RS mission (2013). A Humidified Dual SP2 (HD-SP2), is used to optically size BC-containing particles under dry and humid conditions from which we extract the hygroscopicity parameter, κ, of materials internally mixed with BC. Instrumental variability and the uncertainty of the technique are briefly discussed. We find an ensemble average κ of 0.04 for the set of plumes sampled, consistent with previous estimates of bulk aerosol hygroscopicity from biomass burning sources. The temporal evolution of κ is assessed in the Yosemite Rim Fire plume to constrain the rate of conversion of BC-containing aerosol from hydrophobic to more hydrophilic modes in these emissions. A BC-specific κ increase of ~0.06 over 40 hours is found, fit well with an exponential curve corresponding to a transition from a κ of 0 to a κ of ~0.09 with an e-folding time of 29 hours. Although only a few percent of wildfire particles contain BC, a similar κ increase is estimated for bulk aerosol and we use the measured aerosol composition to infer that the observed κ change is driven by a combination of incorporation of ammonium sulfate and oxidation of existing organic materials. Finally, a substantial fraction of wildfire-generated BC-containing aerosol is calculated to be CCN active shortly after emission likely indicating efficient wet removal. These results can provide important constraints on model treatment of BC from wildfire sources.


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