Collaborative Research: Particulate Nitrate Photolysis as a Daytime Nitrous Acid Source and a Reactive Nitrogen Recycling Pathway in the Troposphere

Health Research Incorporated/New York State Department Of Health, Menands NY

Investigators

Abstract

This project will investigate the hypothesis that photolysis of particulate nitrate in aerosol particles, and to a lesser extent nitrogen dioxide conversion on organic aerosols, are major daytime sources of nitrous acid (HONO) under low nitrogen oxide conditions in the troposphere above the surface boundary layer. Since HONO is readily photolyzed to hydroxyl radical (OH) and nitric oxide, it is further hypothesized that photolysis of particulate nitrate (pNO3) in aerosol particles represents an important pathway to recycle nitric acid/nitrate back to photochemically reactive nitrogen oxides in the troposphere. A series of research activities will be undertaken involving field measurements, laboratory experiments and modeling. Specifically: * Measurements will be made during flights of the NSF/National Center for Atmospheric Research C-130 research aircraft to establish HONO concentration distributions in background continental and oceanic air masses over the southeastern U.S and adjacent coastal waters and to establish relationships between the daytime HONO production and other physical and chemical parameters, including pNO3, particulate organic matter, nitrogen dioxide, ozone, aerosol particle surface area, and solar radiation. * Aerosol samples collected from the C-130 will be used in laboratory experiments to determine the HONO production rate from the photolysis of aerosol pNO3 on filters. * Model calculations will be done based on the results of field measurements and laboratory experiments, to examine pNO3 photolysis and nitrogen dioxide uptake on organic aerosol as a HONO source and investigate if pNO3 photolysis is an efficient re-recycling pathway for nitric acid/nitrate, and * To evaluate the role of this processes in tropospheric photochemistry The research will provide information on the vertical distribution of HONO, nitric acid, pNO3 and other relevant parameters in the troposphere. If the above two hypotheses are proven valid, there are significant atmospheric implications: The troposphere may be more photochemically reactive than generally predicted, due to the remobilized HONO and nitrogen oxides as well as elevated OH levels, generally leading to an enhanced production of ozone and secondary particles. The research may therefore significantly improve our understanding of tropospheric reactive nitrogen chemistry and atmospheric oxidation capacity on regional and global scales. The project will also provide research and training opportunities for postdoctoral researchers, graduate, undergraduate, and high school students in the field of atmospheric chemistry. The research is also relevant to the larger question of air quality and global climate change, i.e., the results from the research will provide useful information regarding atmospheric oxidation capacity and thus insights into how atmospheric pollutants, including some greenhouse gases, are degraded.