ACP Atmospheric Chemistry and Physics ACP 1680-7324 Copernicus GmbH Göttingen, Germany 10.5194/acp-10-12285-2010 Measurements of HONO during BAQS-Met Wentzell J. J. B. 1 2 3 Schiller C. L. 1 2 4 Harris G. W. 1 2 Department of Chemistry, York University, Toronto, Ontario, Canada Centre for Atmospheric Chemistry, York University, Toronto, Ontario, Canada now at: Environment Canada, Science and Technology Branch, Toronto, ON, Canada now at: Environment Canada, Science and Technology Branch, Vancouver, BC, Canada 23 12 2010 10 24 12285 12293 This is an open-access article ditributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. This article is available from http://www.atmos-chem-phys.net/10/12285/2010/acp-10-12285-2010.html The full text article is available as a PDF file from http://www.atmos-chem-phys.net/10/12285/2010/acp-10-12285-2010.pdf

Measurements of nitrous acid (HONO) were performed as part of the 2007 Border Air Quality and Meteorology Study (BAQS-Met) at the Harrow, Ontario, Canada supersite between 20 June and 10 July 2007. Nitrous acid is an important precursor of the hydroxyl radical and understanding its chemistry is important to understanding daytime oxidation chemistry. The HONO measurements were made using a custom built Long Path Absorption Photometer (LOPAP). The goal of this work was to shed light on sources of daytime HONO in the border region. During the course of the campaign HONO mixing ratios consistently exceeded expected daytime values by more than a factor of 6. Mean daytime mixing ratios of 61 pptv were observed. While HONO decay began at sunrise, minimum HONO values were measured during the late afternoon. There was little difference between the daytime (mean = 1.5%) and night-time (mean = 1.7%) ratios of HONO/NO<sub>2</sub>, thus there was a very strong daytime source of HONO which is consistent with other recent studies. Correlations of daytime HONO production with a variety of chemical and meteorological parameters indicate that production is dependent on UV radiation, NO<sub>2</sub> and water vapour but is not consistent with a simple gas phase process. Apparent rate constants for the production of HONO from photolyticaly excited NO<sub>2</sub> and water vapour vary from 2.8–7.8×10<sup>&minus;13</sup> cm<sup>3</sup> molec<sup>−1</sup> s<sup>−1</sup>, during the campaign. These results appear to be consistent with the heterogeneous conversion of NO<sub>2</sub> enhanced by photo-excitation.

 References Acker, K., Möller, D., Wieprecht, W., Meixner, F. X., Bohn, B., Gilge, S., Plass-Dülmer, C., and Berresheim, H.: Strong daytime production of OH from HNO2 at a rural mountain site, Geophys. Res. Lett., 33, L02809, doi:10.1029/2005GL024643, 2006. Alicke, B., Geyer, A., Hofzumahaus, A., Holland, F., Konrad, S., Patz, H. W., Schafer, J., Stutz, J., Volz-Thomas, A., and Platt, U.: OH formation by HONO photolysis during the BERLIOZ experiment, J. Geophys. Res., 108, 8247–8264, 2003. Alicke, B., Platt, U., and Stutz, J.: Impact of nitrous acid photolysis on the total hydroxyl radical budget during the Limitation of Oxidant Production/Pianura Padana Produzione di Ozono study in Milan, J. Geophys. Res., 107, 8196–8213, 2002. Bejan, I., Abd-el-Aal, Y., Barnes, I., Benter, T., Bohn, B., Wiesen, P., and Kleffmann, J.: The photolysis of ortho-nitrophenols: a new gas phase source of HONO, Phys. Chem. Chem. Phys., 8, 2028–2035, 2006. Carr, S., Heard, D. E., and Blitz, M. A.: Comment on Atmospheric Hydroxyl Radical Production from Electronically Excited NO<sub>2</sub> and H<sub>2</sub>O, Science, 324, 336b, 2009. Crowley, J. N. and Carl, S. A.: OH Formation in the Photoexcitation of NO<sub>2</sub> beyond the Dissociation Threshold in the Presence of Water Vapor, J Phys. Chem. A, 101, 4178–4184, 1997. George, C., Strekowski, R. S., Kleffmann, J., Stemmler, K., and Ammann, M.: Photoenhanced uptake of gaseous NO<sub>2</sub> on solid organic compounds: a photochemical source of HONO?, Faraday Discuss., 130, 195–210, 2005. Harris, G. W., Carter, W. P. L., Winer, A. M., Pitts, J. N., Platt, U., and Perner, D.: Observations of nitrous acid in the Los Angeles atmosphere and implications for predictions of ozone-precursor relationships, Environ. Sci. Technol., 16, 414–419, 1982. Heland, J., Kleffmann, J., Kurtenbach, R., and Wiesen, P.: A New Instrument To Measure Gaseous Nitrous Acid (HONO) in the Atmosphere, Environ. Sci. Technol., 35, 3207–3212, 2001. Kleffmann, J.: Daytime sources of nitrous acid (HONO) in the atmospheric boundary layer, Chemphyschem, 8, 1137–1144, 2007. Kleffmann, J., Gavriloaiei, T., Hofzumahaus, A., Holland, F., Koppmann, R., Rupp, L., Schlosser, E., Siese, M. and Wahner, A.: Daytime formation of nitrous acid: A major source of OH radicals in A forest, Geophys. Res. Lett., 32, L05818, doi:10.1029/2005GL022524, 2005. Kleffmann, J., Heland, J., Kurtenbach, R., Lörzer, J., and Wiesen, P.: A New Instrument (LOPAP) for the Measurement of Nitrous Acid (HONO), Environ. Sci. Pollut. Res., 48–54, 2002. Kleffmann, J., Kurtenbach, R., Lörzer, J., Wiesen, P., Kalthoff, N., Vogel, B., and Vogel, H.: Measured and simulated vertical profiles of nitrous acid-Part I: Field Measurements, Atmos. Environ., 37, 2949–2955, 2003. Kraus, A. and Hofzumahaus, A.: Field Measurements of Atmospheric Photolysis Frequencies for O<sub>3</sub>, NO<sub>2</sub>, HCHO, CH<sub>3</sub>CHO, H<sub>2</sub>O<sub>2</sub>, and HONO by UV Spectroradiometry, J. Atmos. Chem., 31, 161–180, 1998. Li, S., Matthews, J., and Sinha, A.: Atmospheric Hydroxyl Radical Production from Electronically Excited NO<sub>2</sub> and H<sub>2</sub>O, Science, 319, 1657–1660, 2008. Ndour, M., D'Anna, B., George, C., Ka, O., Balkanski, Y., Kleffmann, J., Stemmler, K. and Ammann, M.: Photoenhanced uptake of NO<sub>2</sub> on mineral dust: Laboratory experiments and model simulations, Geophys. Res. Lett., 35, L05812, doi:10.1029/2007GL032006, 2008. Platt, U., Perner, D., Harris, G. W., Winer, A. M. and Pitts, J. N.: Observations of nitrous acid in an urban atmosphere by differential optical absorption, Nature, 285, 312–314, 1980. Rohrer,~F and~Berresheim, H.: Strong~correlation~between~levels~of~tropospheric~hydroxyl~ radicals~and~solar~ultraviolet~radiation, Nature,~442,~184–187, 2006 Stemmler, K., Ammann, M., Donders, C., Kleffmann, J., and George, C.: Photosensitized reduction of nitrogen dioxide on humic acid as a source of nitrous acid, Nature, 440, 195–198, 2006. Stemmler, K., Ndour, M., Elshorbany, Y., Kleffmann, J., D'Anna, B., George, C., Bohn, B., and Ammann, M.: Light induced conversion of nitrogen dioxide into nitrous acid on submicron humic acid aerosol, Atmos. Chem. Phys., 7, 4237–4248, doi:10.5194/acp-7-4237-2007, 2007. Stutz, J., Alicke, B., and Neftel, A.: Nitrous acid formation in the urban atmosphere: Gradient measurements of NO<sub>2</sub> and HONO over grass in Milan, Italy, J. Geophys. Res., 107, 8192–8208, 2002. Wall, K. J., Schiller, C. L., and Harris, G. W.: Measurements of the HONO photodissociation constant, J. Atmos. Chem., 55, 31–54, 2006.