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Photochemical Candy: Use of Isomalt as a Proxy Matrix for Secondary Organic Aerosol
AVERY DALTON, Sergey Nizkorodov, University of California, Irvine
Abstract Number: 34
Working Group: Aerosol Chemistry
Abstract
Secondary organic aerosol (SOA) is a complex form of particulate matter that has been found to exist as a liquid, a semi-solid, and an amorphous solid. The roles that chemical environment and viscosity play in the photochemical fate of molecules in SOA are poorly understood. In this work, we characterize the photolysis of 4-nitrocatechol (4NC) in a variety of matrices, including liquid water, liquid isopropyl alcohol, and semi-solid isomalt. The rate of photochemical loss of 4NC was obtained by monitoring the absorbance decay using a custom UV-Vis spectroscopy setup. The photochemical rate constants were found to be greater in an organic environment than in an aqueous solution. The quantum yield of photolysis was found to be smaller in an isomalt glass than in liquid isopropyl alcohol, suggesting photochemical reactivity is affected by matrix viscosity. Ultra-performance liquid chromatography was used in tandem with a photodiode array UV/vis spectrophotometer and high-resolution mass spectrometer to propose photolysis products of 4NC. The primary products formed appeared different between matrices. In solution, most products appeared to result from oxidation of 4NC, in contrast to photoreduction and dimerization products which were more prevalent in solid isomalt. We conclude that the photochemical fate of 4NC, and presumably of other nitrophenols, depends on whether they are in a liquid or semi-solid organic particle.