Measurements of Nitrous Acid (HONO) in an Indiana Forest by Laser Photofragmentation/Laser-induced Flourescence (LP/LIF)

Abstract:

The hydroxyl radical (OH) is an important oxidant in the atmosphere. Reactions of OH with volatile organic compounds (VOCs) initiate a series of reactions that can lead to the production of ozone and secondary aerosols in the atmosphere. An accurate understanding of the major sources of OH is important to develop accurate models of atmospheric chemistry. Nocturnal nitrous acid (HONO) is an important radical resevoir species and releases OH upon photolysis the next morning. Recent studies have indicated higher than expected mixing ratios of HONO during the daytime, suggesting that the production mechanisms of HONO are not fully understood. Additional ambient HONO measurements are necessary to improve our knowledge of the oxidative capacity of the atmosphere.

Measurements of HONO were made during summer 2015 using a Laser Photofragmentation/Laser-induced flourescence (LP/LIF) instrument as part of the Indiana Radical, Reactivity and Ozone Production Intercomparison (IRRONIC). This campaign took place in a forested area in the Indiana Research and Teaching Preserve (IURTP) near the Bloomington Campus. In LP/LIF, ambient air is drawn through a 0.035” diameter inlet and expands into a cell held at ~5 torr . HONO within the sampled air mass is photo-fragmented by laser emision at 355 nm and resulting OH fragments are subsequently detected by laser-induced fluorescence at 308 nm.

In this presentation the development of the LP/LIF insturment will be discussed and preliminary measurements and model comparisons from the campaign will be presented.