Nitrous Acid Chemistry in the Troposphere

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9615748 Zhou This project aims to advance our understanding of the chemistry of nitrous acid (HONO) in the troposphere, including its distribution, its formation mechanisms, and its importance as a source for hydroxyl radicals, and as a recycling pathway for NOx in both urban and clean environments. This knowledge, when incorporated into models, will improve our ability to predict the photoformation of oxidants, such as hydroxyl radicals and ozone, and photodegradation of pollutants on a regional or global scale. Field measurements in urban environments have confirmed that HONO photolysis is a major source for hydroxyl during the morning hours. However, few HONO measurements have been made in clean air masses, due to a lack of sensitive methods. Therefore, the HONO distribution and its importance as a hydroxyl precursor is poorly understood. The exact formation mechanisms of HONO are not well characterized, although it is recognized that atmospheric HONO is formed via heterogeneous reactions involving NOx and nitric acid. In this project, a highly sensitive technique for atmospheric measurements of HONO will be developed. It will be based on aqueous scrubbing of HONO using a coil sampler, followed by derivatization with 2,4-dinitrophenylhydrazine and determination of the azide formed using HPLC with UV-detection. The detection limit of this technique will be less than 1 pptv with a time resolution of ten minutes. This technique will be used to establish the distribution of HONO along with a suite of chemical and meteorological parameters in both polluted and clean air masses, during four two-week intensive measurements in downtown Albany, NY, and one one-month intensive campaign at the summit of Whiteface Mountain, NY. A box model will be constructed and used to verify suggested formation mechanisms by comparing the predicted and measured HONO distributions, and to obtain information on the importance of HONO in tropospheric chemistry. ***