Nitrous acid is a photochemical source of hydroxyl radical that plays an important role in initiating radical reactions leading to ozone and aerosol formation in the lower atmosphere. Previous studies have determined that when irradiated with UV-visible light, humic acids facilitate the conversion of nitrogen dioxide to nitrous acid via electron transfer from photo-reduced chromophores. The amount of nitrous acid generated depends on the nitrogen dioxide concentration, relative humidity, light intensity and amount of humic acid present in the substrate. Here, we present results of cavity-enhanced absorption spectroscopy measurements of nitrous acid emitted when humic acids are exposed to known amounts of nitrogen dioxide under dark and light conditions. Nitrogen dioxide uptake kinetics and HONO conversion yields were examined. The reactivity differences between humic acids from various terrestrial and aquatic sources were assessed and compared them to the chemical and physical properties of the substrate. The resulting trends are useful for understanding the role of natural organic matter in promoting heterogeneous HONO formation on ground surfaces.

Reactivity differences of humic acids and their influence on nitrogen dioxide reduction in the terrestrial environment

251st National Meeting (2016)

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