Light absorbing organic aerosols, referred to as brown carbon, can have an important climate impact through the absorption of solar radiation. Nitrophenol compounds have been identified in ambient brown carbon aerosol associated with biomass burning and contribute strongly to the light absorption of the aerosol. Recent studies have shown that ambient brown carbon aerosols can be bleached of their colour by direct photolysis and photo-oxidation during atmospheric aging. However, the photo-oxidation of nitrophenols shows an enhancement in light absorption before it is lost. The mechanism of this absorption enhancement and the fate of nitrophenol compounds is investigated in the aqueous phase photo-oxidation of three characteristic nitrophenols: 4-nitrocatechol, 2,4-dinitrophenol, and 5-nitroguaiacol. Chemical composition throughout the reaction is monitored online with the aerosol-chemical ionization mass spectrometer (Aerosol-CIMS) and light absorption is measured offline with UV/Vis spectroscopy. The kinetics and mechanism of nitrophenol photo-oxidation are examined to better understand the fate of nitrophenol compounds and the evolution of light absorption under aqueous aerosol or cloud water conditions.

Aqueous phase photo-oxidation of nitrophenol brown carbon compounds

254th National Meeting (2017)

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