Development of a Laser Photofragmentation/ Laser-Induced Fluorescence Instrument for Tropospheric Measurements of Nitrous Acid

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This project involves the development of a Laser Photofragmentation/Laser Induced Fluorescence instrument for measuring tropospheric concentrations of HONO. Ambient air will be expanded into a low-pressure cell and HONO will be fragmented into OH and NO by photolysis at 355 nm. The OH photofragment will be quantified using the Fluorescent Assay by Gas Expansion (FAGE) approach at 308 nm. It is anticipated that this new instrument will combine the selectivity of spectroscopic techniques and the low detection limit observed for chemical techniques, making it of prime interest for the scientific community. This new instrument will be fully characterized in the laboratory and it is anticipated to perform initial field measurements in an urban atmosphere. HONO will be measured in addition to OH and NO to determine if unknown sources of HONO are occurring in the atmosphere of Bloomington, IN.An incomplete description of the major sources of HONO in current models of atmospheric chemistry may have important implications for air quality control strategies as it may lead to an underprediction of the concentrations of photochemical pollutants. For example, ozone and secondary organic aerosols are of particular interest to the society due to detrimental effects on human health. In addition, an accurate description of the main sources of free radicals is important to issues of climate change as atmospheric oxidation processes control the lifetime of greenhouse gases and the alternative chlorofluorocarbons, which have a significant impact on the radiative budget of earth. Future deployments of this instrument during field campaigns as well as its use during laboratory studies will provide additional insights in the HONO chemistry occurring in the atmosphere and will help improve actual models of atmospheric chemistry. Future intercomparisons of this instrument with other measurement techniques will also help in assessing the accuracy of HONO measurements in the atmosphere.