AAAR 33rd Annual Conference
October 20 - October 24, 2014
Rosen Shingle Creek
Orlando, Florida, USA
Abstract View
Photochemical Aging of Brown Carbon Aerosols
Paige Aiona, Hyun Ji Lee, Alexander Laskin, Julia Laskin, SERGEY NIZKORODOV, University of California, Irvine
Abstract Number: 50 Working Group: Aerosol Chemistry
Abstract Atmospheric aerosols directly influence climate because of their ability to scatter and absorb solar and terrestrial radiation. Primary sources such as biomass burning as well as secondary heterogeneous atmospheric reactions have been shown to produce “brown carbon” (BrC) organic aerosols capable of absorbing visible and near-ultraviolet radiation. Nitrogen-containing organic compounds (NOC) appear to be a quintessential element of BrC, and they may be solely responsible for the high absorption coefficients of BrC. The goal of our research is to investigate photochemical stability of different types of BrC and to address the role of NOC in controlling the light-absorption properties of BrC. We are presenting results of smog chamber experiments and bulk aqueous phase experiments that examine the production and photodegradation of BrC in reactions between reduced nitrogen compounds (ammonia and amines) and common organic carbonyls. Specifically, we focus on reactions of 1,4-dicarbonyls, which appear to efficiently produce stable heterocyclic organic compounds in the presence of reduced nitrogen compounds. BrC produced by biomass burning is investigated for comparison. UV-Vis spectroscopy is used to measure the mass absorption coefficients of BrC and high resolution mass spectroscopy is used to investigate its molecular level composition. In addition, photolysis of BrC by actinic radiation is investigated in order to predict its effective lifetime with respect to photodegradation. We observe that BrC resulting from biomass burning is relatively stable with respect to photodegradation, whereas BrC produced in secondary reactions of carbonyls is highly photolabile. This study underscores the highly variable nature of BrC, which complicates representation of BrC in climate and air-pollution models.