Nitrous acid (HONO), nitric acid (HNO3), and organic aerosol were measured simultaneously atop an 18-story tower in Houston, TX during August and September of 2006. HONO and HNO3 were measured using a mist chamber/ion chromatographic technique, and aerosol size and chemical composition were determined using an Aerodyne quadrupole aerosol mass spectrometer. Observations indicate the potential for a new HONO formation pathway: heterogeneous conversion of HNO3 on the surface of primary organic aerosol (POA). Significant HONO production was observed, with an average of 0.97ppbvevent-1 and a maximum increase of 2.2ppb in 4h. Nine identified events showed clear HNO3 depletion and well-correlated increases in both HONO concentration and POA-dominated aerosol surface area (SA). Linear regression analysis results in correlation coefficients (r2) of 0.82 for HONO/SA and 0.92 for HONO/HNO3. After correction for established HONO formation pathways, molar increases in excess HONO (HONOexcess) and decreases in HNO3 were nearly balanced, with an average HONOexcess/HNO3 value of 0.97. Deviations from this mole balance indicate that the residual HNO3 formed aerosol-phase nitrate. Aerosol mass spectral analysis suggests that the composition of POA could influence HONO production. Several previously identified aerosol-phase PAH compounds were enriched during events, suggesting their potential importance for heterogeneous HONO formation. © 2008 Elsevier Ltd.
CITATION STYLE
Ziemba, L. D., Dibb, J. E., Griffin, R. J., Anderson, C. H., Whitlow, S. I., Lefer, B. L., … Flynn, J. (2010). Heterogeneous conversion of nitric acid to nitrous acid on the surface of primary organic aerosol in an urban atmosphere. Atmospheric Environment, 44(33), 4081–4089. https://doi.org/10.1016/j.atmosenv.2008.12.024
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