Investigations of the Photochemical HONO Formation Reactions of Atmospheric Importance

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This research is focused on determining the sources of nitrous acid to the atmosphere. Nitrous acid can form hydroxyl radical, an important compound responsible for creating the air pollutant ozone. Nitrous acid can be produced on some environmental surfaces, in the presence of water and nitrogen dioxide. Quantifying the relative importance of the sources of nitrous acid to the atmosphere will improve the understanding of some of the causes of air pollution and climate change.The objective of this research is to characterize and quantify photochemical sources of nitrous acid (HONO), an important precursor to the hydroxyl radical (OH). The photolysis of HONO significantly influences atmospheric pollutant oxidation and ozone production. Recent laboratory studies have shown that nitrophenols formed from the dark reaction of nitrogen dioxide (NO2) with surface adsorbed polyphenolic compounds and the subsequent photolysis of surface-adsorbed nitrophenols may be a substantial source of HONO. But wavelength-dependent HONO yields, from the photolysis of the adsorbed nitrophenols, have not been characterized. This work will quantify photochemical HONO and the OH quantum yields from heterogeneous and gas phase photolysis reactions using laser photolysis combined with cavity ring-down spectroscopy and determine the UV/visible absorption cross sections of surface-adsorbed NO3 and nitrophenols as a function of wavelength using Brewster angle cavity ringdown spectroscopy. Additional experiments will provide data on the absorption cross sections of gas phase nitrophenols and HONO yields from nitrate and 2-nitrophenol adsorbed on surfaces that serve as surrogates for various environmentally relevant surfaces.