Atmospheric particles that preferentially absorb at shorter visible wavelengths are referred to as brown carbon aerosol. These particles may have both primary and secondary sources in the atmosphere, and they have a direct effect on climate. Recent field observations indicate that reduction of particle absorptivity can occur with increasing atmospheric residence time, thus lessening the climate impact of brown carbon. This talk will present the results of laboratory investigations into the fundamental nature and chemical aging of laboratory surrogates of atmospheric brown carbon aerosol material. First, mechanistic experiments did not find evidence for colour arising from charge-transfer complexes in the aqueous phase. Both pure compounds and wood pyrolysis products were analyzed. Second, the aqueous-phase aging of these materials by both light and OH radicals led to loss of colour at long exposure times, with OH oxidation having the dominant effect. Finally, heterogeneous aging of aerosol particles by the gas-phase OH radical can also lead to substantial loss of absorptivity for atmospherically relevant exposures, with the particle viscosity playing an important role in controlling the bleaching rate.

Chemical aging of brown carbon aerosol material

2019 Fall National Meeting

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