AAAR 35th Annual Conference October 17 - October 21, 2016 Oregon Convention Center Portland, Oregon, USA
Abstract View
Aqueous Phase Photo-oxidation of Nitroaromatic Compounds in Brown Carbon Aerosol
RACHEL HEMS, Jonathan Abbatt, University of Toronto, Canada
Abstract Number: 57 Working Group: Aerosol Chemistry
Abstract Light absorbing organic aerosols, referred to as brown carbon, are geographically widespread and can have an important climate impact through the absorption of solar radiation. The sources of brown carbon aerosols are thought to be primarily biomass or fossil fuel burning, but with contributions from secondary reactions in aqueous aerosol or cloud droplets, for example reaction of aldehydes and amines. Despite ongoing research in this field, little is known about the chemical composition of brown carbon aerosols, specifically the chromophores responsible for the colour, and their atmospheric transformations. Recent studies, both in the laboratory and the field, have shown that brown carbon aerosols can be bleached of their colour by direct photolysis and photo-oxidation reactions on the timescale of hours to days. However, the photo-oxidation of nitrophenols, coloured compounds often associated with biomass burning organic aerosol, show an enhancement in light absorption before the colour is lost. The mechanism of this colour enhancement and the fate of nitrophenol compounds in aqueous aerosol is investigated in the aqueous phase photo-oxidation of 4-nitrocatechol. Chemical composition is monitored online throughout the reaction with the aerosol-chemical ionization mass spectrometer and light absorption is measured offline with UV/Vis spectroscopy. We studied the kinetics of the reaction and its products to gain a better understanding of brown carbon aerosol aging and the evolution of its light absorptivity. A mechanistic understanding of photo-oxidation of nitroaromatic species can help to better model light absorbing organic aerosol.