ACP Atmospheric Chemistry and Physics ACP 1680-7324 Copernicus GmbH Göttingen, Germany 10.5194/acp-12-9977-2012 Impact of HONO on global atmospheric chemistry calculated with an empirical parameterization in the EMAC model Elshorbany Y. F. 1 2 Steil B. 1 Brühl C. 1 Lelieveld J. 1 3 4 Max-Plank Institute for Chemistry, Atmospheric Chemistry Department, Mainz, Germany National Research Center, Environmental Sciences Research Division, Cairo, Egypt The Cyprus Institute, Nicosia, Cyprus King Saud University, Riyadh, Saudi Arabia 30 10 2012 12 20 9977 10000 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/12/9977/2012/acp-12-9977-2012.html The full text article is available as a PDF file from http://www.atmos-chem-phys.net/12/9977/2012/acp-12-9977-2012.pdf

The photolysis of HONO is important for the atmospheric HO<sub>x</sub> (OH + HO<sub>2</sub>) radical budget and ozone formation, especially in polluted air. Nevertheless, owing to the incomplete knowledge of HONO sources, realistic HONO mechanisms have not yet been implemented in global models. We investigated measurement data sets from 15 field measurement campaigns conducted in different countries worldwide. It appears that the HONO/NO<sub>x</sub> ratio is a good proxy predictor for HONO mixing ratios under different atmospheric conditions. From the robust relationship between HONO and NO<sub>x</sub>, a representative mean HONO/NO<sub>x</sub> ratio of 0.02 has been derived. Using a global chemistry-climate model and employing this HONO/NO<sub>x</sub> ratio, realistic HONO levels are simulated, being about one order of magnitude higher than the reference calculations that only consider the reaction OH + NO → HONO. The resulting enhancement of HONO significantly impacts HO<sub>x</sub> levels and photo-oxidation products (e.g, O<sub>3</sub>, PAN), mainly in polluted regions. Furthermore, the relative enhancements in OH and secondary products are higher in winter than in summer, thus enhancing the oxidation capacity in polluted regions, especially in winter when other photolytic OH sources are of minor importance. Our results underscore the need to improve the understanding of HONO chemistry and its representation in atmospheric models.

 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 HNO<sub>2</sub> at a Rural Mountain Site, Geophys. Res. Lett., 33, L02809, http://dx.doi.org/10.1029/2005GL024643doi:10.1029/2005GL024643, 2006. 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, http://dx.doi.org/10.1029/2000JD000075doi:10.1029/2000JD000075, 2002. Alicke, B., Geyer, A., Hofzumahaus, A., Holland, F., Konrad, S., Pätz, H. W., Schäfer, J., Stutz, J., Volz-Thomas, A. and Platt, U.: OH formation by HONO photolysis during the BERLIOZ experiment, J. Geophys. Res., 108, 8247, http://dx.doi.org/10.1029/2001JD000579doi:10.1029/2001JD000579, 2003. Atkinson, R., Baulch, D. L., Cox, R. A., Crowley, J. N., Hampson, R. F., Hynes, R. G., Jenkin, M. E., Rossi, M. J., and Troe, J.: Evaluated kinetic and photochemical data for atmospheric chemistry: Volume I – gas phase reactions of Ox, HO$_\text x$, NO$_\text x$ and SO$_\text x$ species, Atmos. Chem. Phys., 4, 1461–1738, http://dx.doi.org/10.5194/acp-4-1461-2004doi:10.5194/acp-4-1461-2004, 2004. Aumont, B., Chervier, F., and Laval, S.: Contribution of HONO sources to the NO$_\text x$/HO$_\text x$/O<sub>3</sub> chemistry in the polluted boundary layer, Atmos. Environ., 37, 487–498, 2003. 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, http://dx.doi.org/10.1039/b516590cdoi:10.1039/b516590c, 2006. Brühl, C., Lelieveld, J., Crutzen, P. J., and Tost, H.: The role of carbonyl sulphide as a source of stratospheric sulphate aerosol and its impact on climate, Atmos. Chem. Phys., 12, 1239–1253, http://dx.doi.org/10.5194/acp-12-1239-2012doi:10.5194/acp-12-1239-2012, 2012. Clapp, L. J. and Jenkin, M.: Analysis of the relationship between ambient levels of O<sub>3</sub>, NO<sub>2</sub> and NO as a function of NO$_\text x$ in the UK, Atmos. Environ., 35, 6391–6405, 2001. Czader, B. H., Rappenglück, B., Percell, P., Byun, D. W., Ngan, F., and Kim, S.: Modeling nitrous acid and its impact on ozone and hydroxyl radical during the Texas Air Quality Study 2006, Atmos. Chem. Phys., 12, 6939–6951, http://dx.doi.org/10.5194/acp-12-6939-2012doi:10.5194/acp-12-6939-2012, 2012. Dusanter, S., Vimal, D., Stevens, P. S., Volkamer, R., Molina, L. T., Baker, A., Meinardi, S., Blake, D., Sheehy, P., Merten, A., Zhang, R., Zheng, J., Fortner, E. C., Junkermann, W., Dubey, M., Rahn, T., Eichinger, B., Lewandowski, P., Prueger, J., and Holder, H.: Measurements of OH and HO2 concentrations during the MCMA-2006 field campaign – Part 2: Model comparison and radical budget, Atmos. Chem. Phys., 9, 6655–6675, http://dx.doi.org/10.5194/acp-9-6655-2009doi:10.5194/acp-9-6655-2009, 2009. Elshorbany, Y. F., Kurtenbach, R., Wiesen, P., Lissi, E., Rubio, M., Villena, G., Gramsch, E., Rickard, A. R., Pilling, M. J., and Kleffmann, J.: Oxidation capacity of the city air of Santiago, Chile, Atmos. Chem. Phys., 9, 2257-2273, http://dx.doi.org/10.5194/acp-9-2257-2009doi:10.5194/acp-9-2257-2009, 2009a. Elshorbany, Y. F., Kleffmann, J., Kurtenbach, R., Rubio, M., Lissi, E., Villena, G., Gramsch, E., Rickard, A. R., Pilling, M. J., and Wiesen, P.: Summertime photochemical ozone formation in Santiago, Chile, Atmos. Environ., 43, 6398–6407 http://dx.doi.org/10.1016/j.atmosenv.2009.08.047doi:10.1016/j.atmosenv.2009.08.047, 2009b. Elshorbany, Y. F., Kleffmann, J., Kurtenbach, R., Lissi, E., Rubio, M., Villena, G., Gramsch, E., Rickard, A. R., Pilling, M. J., and Wiesen, P.: Seasonal dependence of the oxidation capacity of the city of Santiago de Chile, Atmos. Environ., 44, 5383–5394, http://dx.doi.org/10.1016/j.atmosenv.2009.08.036doi:10.1016/j.atmosenv.2009.08.036, 2010a. Elshorbany, Y. F., Barnes, I., Becker, K. H., Kleffmann, J., and Wiesen, P.: Sources and Cycling of Tropospheric Hydroxyl Radicals – An Overview, Z. Phys. Chem., 224, 967–987, 2010b. Elshorbany, Y. F., Kleffmann, J., Hofzumahaus, A., Kurtenbach, R., Wiesen, P., Dorn,H.-P., Schlosser, E., Brauers, T., Fuchs, H., Rohrer, F., Wahner, A., Kanaya, Y., Yoshino, A., Nishida, S., Kajii, Y., Martinez, M., Rudolf, M., Harder, H., Lelieveld, J., , Elste, T., Plass-Dülmer, C., Stange, G., and Berresheim, H.: HO$_\text x$ Budgets during HOxComp: a Case Study of HO$_\text x$ Chemistry under NO$_\text x$ limited Conditions, J. Geoophys. Res., 117, D03307, http://dx.doi.org/10.1029/2011JD017008doi:10.1029/2011JD017008, 2012. Febo, A., Perrino, C., and Allegrini, I.: Measurement of Nitrous Acid in Milan, Italy, by DOAS and Diffusion Denuders, Atmos. Environ., 30, 3599–3609, 1996. Febo, A., Perrino, C., Bruno, P., and Mazziotti C.: FORMONA final report to the European Commission, Consiglio Nationale delle Ricerche, Rome, 1999. Fortuin, J. P. F. and Kelder, H.: An ozone climatology based on ozonesonde and satellite measurements, J. Geophys. Res., 103, 31709–31734, 1998. Gonc\calves, M., Dabdub, D., Chang, W. L., Jorba, O., and Baldasano, J. M.: Impact of HONO sources on the performance of mesoscale air quality models, Atmos. Environ., 54, 168–176, http://dx.doi.org/10.1016/j.atmosenv.2012.02.079doi:10.1016/j.atmosenv.2012.02.079, 2012. Harris, G. W., Carter,W. P. L.,Winer, A. M., Pitts Jr., J. N., Platt, U., and Perner, D.: Observation 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. Huang, G., Zhou, X., Deng, G., Qiao, H., and Civerolo, K.: Measurements of atmospheric nitrous acid and nitric acid, Atmos. Environ., 36, 2225–2235, 2002. Jöckel,~P., Sander,~R., Kerkweg,~A., Tost,~H., and Lelieveld,~J.: Technical Note: The Modular Earth Submodel System (MESSy) – a new approach towards Earth System Modeling, Atmos. Chem. Phys., 5, 433–444, http://dx.doi.org/10.5194/acp-5-433-2005doi:10.5194/acp-5-433-2005, 2005. Jöckel,~P., Tost,~H., Pozzer,~A., Brühl,~C., Buchholz,~J., Ganzeveld,~L., Hoor,~P., Kerkweg,~A., Lawrence,~M G., Sander,~R., Steil,~B., Stiller,~G., Tanarhte,~M., Taraborrelli,~D., van~Aardenne,~J., and Lelieveld,~J.: The atmospheric chemistry general circulation model ECHAM5/MESSy1: consistent simulation of ozone from the surface to the mesosphere, Atmos. Chem. Phys., 6, 5067–5104, http://dx.doi.org/10.5194/acp-6-5067-2006doi:10.5194/acp-6-5067-2006, 2006. Jorba, O., Dabdub, D., Blaszczak-Boxe, C., Perez, C., Janjic, Z., Baldasano, J. M., Spada, M., Badia, A., Goncalves, M.: Potential Significance of Photoexcited NO<sub>2</sub> on Global Air Quality with the NMMB/BSC Chemical Transport Model, J. Geophys. Res., 117, D13301, http://dx.doi.org/10.1029/2012JD017730doi:10.1029/2012JD017730, 2012. Kerkweg, A., Sander, R., Tost, H., and Jöckel, P.: Technical note: Implementation of prescribed (OFFLEM), calculated (ONLEM), and pseudo-emissions (TNUDGE) of chemical species in the Modular Earth Submodel System (MESSy), Atmos. Chem. Phys., 6, 3603–3609, http://dx.doi.org/10.5194/acp-6-3603-2006doi:10.5194/acp-6-3603-2006, 2006. Kleffmann, J., Heland, J., Kurtenbach, R., Lörzer, J. C., and Wiesen, P.: A New Instrument (LOPAP) for the Detection of Nitrous Acid (HONO), Environ. Sci. Technol., 9, 48–54, 2002. Kleffmann, J., Kurtenbach, R., Lörzer, J. C., 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. 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, http://dx.doi.org/10.1029/2005GL022524doi:10.1029/2005GL022524, 2005. Kleffmann, J., Lörzer, J. C., Wiesen, P., Kern, C., Trick, S., Volkamer, R., Rodenas, M., and Wirtz, K.: Intercomparisons of the DOAS and LOPAP Techniques for the Detection of Nitrous Acid (HONO) in the Atmosphere, Atmos. Environ., 40, 3640–3652, 2006. Kleffmann, J.: Daytime Sources of Nitrous Acid (HONO) in the Atmospheric Boundary Layer, Chem. Phys. Chem., 8, 1137–1144, 2007. Kleffmann, J. and Wiesen, P.: Technical Note: Quantification of Interferences of Wet Chemical HONO LOPAP Measurements under Simulated Polar Conditions, Atmos. Chem. Phys., 8, 6813–6822, http://dx.doi.org/10.5194/acp-8-6813-2008doi:10.5194/acp-8-6813-2008, 2008. Kulmala, M. and Petäjä T.: Soil nitrites influence atmospheric chemistry, Science, 333, 1586–1587, http://dx.doi.org/10.1126/science.1211872doi:10.1126/science.1211872, 2011. Kurtenbach, R., Becker, K. H., Gomes, J. A. G., Kleffmann, J., Lörzer, J. C., Spittler, M., Wiesen, P., Ackermann, R., Geyer, A., and Platt, U.: Investigation of Emissions and Heterogeneous Formation of HONO in a Road Traffic Tunnel, Atmos. Environ., 35, 3385–3394, 2001. Lelieveld, J., Peters, W., Dentener F. J., and Krol, M. C.: Stability of tropospheric hydroxyl chemistry, J. Geophys. Res., 107, 4715, http://dx.doi.org/10.1029/2002JD002272doi:10.1029/2002JD002272, 2002. Lelieveld, J., Brühl, C., Jöckel, P., Steil, B., Crutzen, P. J., Fischer, H., Giorgetta, M. A., Hoor, P., Lawrence, M. G., Sausen, R., and Tost, H.: Stratospheric dryness: model simulations and satellite observations, Atmos. Chem. Phys., 7, 1313–1332, http://dx.doi.org/10.5194/acp-7-1313-2007doi:10.5194/acp-7-1313-2007, 2007. Li,~G., Lei,~W., Zavala,~M., Volkamer,~R., Dusanter,~S., Stevens,~P., and Molina,~L T.: Impacts of HONO sources on the photochemistry in Mexico City during the MCMA-2006/MILAGO Campaign, Atmos. Chem. Phys., 10, 6551–6567, http://dx.doi.org/10.5194/acp-10-6551-2010doi:10.5194/acp-10-6551-2010, 2010. 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. Li,~X., Brauers,~T., Häseler,~R., Bohn,~B., Fuchs,~H., Hofzumahaus,~A., Holland,~F., Lou,~S., Lu,~K D., Rohrer,~F., Hu,~M., Zeng,~L M., Zhang,~Y H., Garland,~R M., Su,~H., Nowak,~A., Wiedensohler,~A., Takegawa,~N., Shao,~M., and Wahner,~A.: Exploring the atmospheric chemistry of nitrous acid (HONO) at a rural site in Southern China, Atmos. Chem. Phys., 12, 1497–1513, http://dx.doi.org/10.5194/acp-12-1497-2012doi:10.5194/acp-12-1497-2012, 2012. Li, Y., An, J., Min, M., Zhang, W., Wang, F., and Xie, P.: Impacts of HONO sources on the air quality in Beijing, Tianjin and Hebei province of china, Atmos. Environ., 45, 4735–4744, http://dx.doi.org/10.1016/j.atmosenv.2011.04.086doi:10.1016/j.atmosenv.2011.04.086, 2011. Lu, K., Zhang, Y., Su, H., Brauers, T., Chou, C. C., Hofzumahaus, A., Liu, S. C., Kita, K., Kondo, Y., Shao, M., Wahner, A., Wang, J., Wang, X., and Zhu, T.: Oxidant (O$_3+$ NO<sub>2</sub>) production processes and formation regimes in Beijing, J. Geophys. Res., 115, D07303, http://dx.doi.org/10.1029/2009JD012714doi:10.1029/2009JD012714, 2010. New York State Department of Environmental Conservation, 2005 ozone exceedences in New York State, http://www.dec.ny.gov/docs/air_pdf/05o3exc.pdf, (last access: 22 May 2012), 2006. 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, http://dx.doi.org/10.1029/2007GL032006doi:10.1029/2007GL032006, 2008. Ortega, J., Helmig, D., Guenther, A., Harley, P., Pressley, S., and Vogel, C.: Flux estimates and OH reaction potential of reactive biogenic volatile compounds (BVOCs) from a mixed northern hardwood forest, Atmos. Environ., 41, 5479–5495, 2007. Perner, D. and Platt, U.: Detection of Nitrous Acid in the Atmosphere by Differential Optical Absorption, J. Geophys. Res., 6, 917–920, 1979. Platt, U. and Perner, D.: Direct Measurements of Atmospheric CH<sub>2</sub>O, HNO<sub>2</sub>, O<sub>3</sub>, NO<sub>2</sub>, and SO<sub>2</sub> by Differential Optical Absorption in the Near UV, J. Geophys. Res., 85, 7453–7458, 1980. Pöschl, U., von Kuhlmann, R., Poisson, N., and Crutzen, P. J.: Development and intercomparison of condensed isoprene oxidation mechanisms for global atmospheric modeling, J. Atmos. Chem., 37, 29–52, 2000. Pozzer, A., Jöckel, P., Tost, H., Sander, R., Ganzeveld, L., Kerkweg A., and Lelieveld, J.: Simulating organic species with the global atmospheric chemistry general circulation model ECHAM5/MESSy1: a comparison of model results with observations, Atmos. Chem. Phys., 7, 2527–2550, http://dx.doi.org/10.5194/acp-7-2527-2007doi:10.5194/acp-7-2527-2007, 2007. Pozzer, A., Pollmann, J., Taraborrelli, D., Jöckel, P., Helmig, D., Tans, P., Hueber J., and Lelieveld, J.: Observed and simulated global distribution and budget of atmospheric C$_2-$C$_5$ alkanes, Atmos. Chem. Phys.,~10,~4403–4422, http://dx.doi.org/10.5194/acp-10-4403-2010doi:10.5194/acp-10-4403-2010, 2010. Pozzer, A., de~Meij, A., Pringle, K. J., Tost, H.,~Doering, U. M., van~Aardenne, J., and Lelieveld, J.: Distributions and regional budgets of aerosols and their precursors simulated with the EMAC chemistry-climate model, Atmos. Chem. Phys., 12, 961–987, http://dx.doi.org/10.5194/acp-12-961-2012doi:10.5194/acp-12-961-2012, 2012. Ren, X., Harder, H., Martinez, M., Lesher, R. L., Oliger, A., Simpas, J. B., Brune, W. H., Schwab, J. J., Demerjian, K. L., He, Y., Zhou, X., and Gao, H.: OH and HO<sub>2</sub> Chemistry in the Urban Atmosphere of New York City, Atmos. Environ., 37, 3639–3651, 2003. Ren, X., Brune, W. H., Mao, J., Mitchell, M. J., Lesher, R. L., Simpas, J. B., Metcalf, A. R., Schwab, J.J., Cai, C., Li, Y., Demerjian, K. L., Felton, H. D., Boynton, G., Adams, A., Perry, J., He, Y., Zhou, X. and Hou, J.: Behavior of OH and HO<sub>2</sub> in the Winter Atmosphere in New York City, Atmos. Environ., 40, Supplement 2, 252–263, 2006. Ren,~X., Gao,~H., Zhou,~X., Crounse,~J D., Wennberg,~P O., Browne,~E C., LaFranchi,~B W., Cohen,~R C., McKay,~M., Goldstein,~A H., and Mao,~J.: Measurement of atmospheric nitrous acid at Blodgett Forest during BEARPEX2007, Atmos. Chem. Phys., 10, 6283–6294, http://dx.doi.org/10.5194/acp-10-6283-2010doi:10.5194/acp-10-6283-2010, 2010. Roeckner, E., Brokopf, R., Esch, M., Giorgetta, M., Hagemann, S., Kornblueh, L., Manzini, E., Schlese, U., and Schulzweida, U.: Sensitivity of simulated climate to horizontal and vertical resolution in the ECHAM5 atmosphere model, J. Climate, 19, 3771– 3791, 2006. Sander, R., Kerkweg, A., Jöckel, P., and Lelieveld, J.: Technical note: The new comprehensive atmospheric chemistry module MECCA, Atmos. Chem. Phys. 5, 445–450, http://dx.doi.org/10.5194/acp-5-445-2005doi:10.5194/acp-5-445-2005, 2005. Sörgel,~M., Regelin,~E., Bozem,~H., Diesch,~J.-M., Drewnick,~F., Fischer,~H., Harder,~H., Held,~A., Hosaynali-Beygi,~Z., Martinez,~M., and Zetzsch,~C.: Quantification of the unknown HONO daytime source and its relation to NO<sub>2</sub>, Atmos. Chem. Phys., 11, 10433–10447, http://dx.doi.org/10.5194/acp-11-10433-2011doi:10.5194/acp-11-10433-2011, 2011a. Sörgel, M., Trebs, I., Serafimovich, A., Moravek, A., Held, A., and Zetzsch, C.: Simultaneous HONO measurements in and above a forest canopy: influence of turbulent exchange on mixing ratio differences, Atmos. Chem. Phys., 11, 841–855, http://dx.doi.org/10.5194/acp-11-841-2011doi:10.5194/acp-11-841-2011, 2011b. Stemmler, K., Ammann, M., Dondors, C., Kleffmann, J., and George, C.: Photosensitized Reduction of Nitrogen Dioxide on Humic Acid as a Source of Nitrous Acid, Nature, 440, 195–198, http://dx.doi.org/10.1038/nature04603doi:10.1038/nature04603, 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, http://dx.doi.org/10.5194/acp-7-4237-2007doi: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, http://dx.doi.org/10.1029/2001JD000390doi:10.1029/2001JD000390, 2002. Su, H., Cheng, Y. F., Shao, M., Gao, D. F., Yu, Z. Y., Zeng, L. M., Slanina, J., Zhang, Y. H., and Wiedensohler, A.: Nitrous acid (HONO) and its daytime sources at a rural site during the 2004 PRIDE-PRD experiment in China, J. Geophys. Res., 113, D14312, http://dx.doi.org/10.1029/2007JD009060doi:10.1029/2007JD009060, 2008. Su, H., Cheng, Y., Oswald, R., Behrendt, T., Trebs, I., Meixner, F. X., Andreae, M. O., Cheng, P., Zhang, Y., and Pöschl, U.: Soil Nitrite as a Source of Atmospheric HONO and OH Radicals, Science, 333, 1616–1618, http://dx.doi.org/10.1126/science.1207687doi:10.1126/science.1207687, 2011. Taraborrelli, D., Lawrence, M. G., Butler, T. M., Sander, R., and Lelieveld, J.: Mainz Isoprene Mechanism 2 (MIM2): an isoprene oxidation mechanism for regional and global atmospheric modelling, Atmos. Chem. Phys., 9, 2751–2777, http://dx.doi.org/10.5194/acp-9-2751-2009doi:10.5194/acp-9-2751-2009, 2009. Tost, H., Jöckel, P., Kerkweg, A., Pozzer, A., Sander, R., and Lelieveld, J.: Global cloud and precipitation chemistry and wet deposition: tropospheric model simulations with ECHAM5/MESSy1, Atmos. Chem. Phys., 7, 2733–2757, http://dx.doi.org/10.5194/acp-7-2733-2007doi:10.5194/acp-7-2733-2007, 2007. van Aalst, M. K., van den Broek, M. M. P., Bregman, A., Brühl, C., Steil, B., Toon, G. C., Garcelon, S., Hansford, G. M., Jones, R. L., Gardiner, T. D., Roelofs, G.-J., Lelieveld, J., and Crutzen, P. J.: Trace gas transport in the 1999/2000 Arctic; comparison of nudged GCM runs with observations, Atmos. Chem. Phys., 4, 81–93, http://dx.doi.org/10.5194/acp-4-81-2004doi:10.5194/acp-4-81-2004, 2004. Veitel, H.: Vertical profiles of NO<sub>2</sub> and HONO in the boundary layer, PhD Thesis, University of Heidelberg, http://archiv.ub.uni-heidelberg.de/volltextserver/volltexte/2002/2490/pdf/DissVeitel2002.pdf, (last access: 22 May 2012), 2002. Villena, G., Kleffmann, J, Kurtenbach, R., Wiesen, P., Lissi, E., Rubio, M. A., Croxatto, J., and Rappenglück, B., Vertical gradients of HONO, NO$_\text x$ and O<sub>3</sub> in Santiago de Chile, Atmos. Environ. 45, 3867–3873, 2011a. Villena, G., Wiesen,P., Cantrell, C. A., Flocke, F., Fried, A., Hall, S. R., Hornbrook, R. S., Knapp, D., Kosciuch, E., Mauldin III, R. L., McGrath, J. A., Montzka, D., Richter, D., Ullmann, K., Walega, J., Weibring, P., Weinheimer, A., Staebler, R. M., Liao, J., Huey, L. G., and Kleffmann, J.: Nitrous acid (HONO) during polar spring in Barrow, Alaska: A net source of OH radicals?, J. Geophys. Res., 116, D00R07, http://dx.doi.org/10.1029/2011JD016643doi:10.1029/2011JD016643, 2011b. Vogel, B., Vogel, H., Kleffmann, J., and Kurtenbach, R.: Measured and Simulated Vertical Profiles of Nitrous Acid, Part II – Model Simulations and Indications for a Photolytic Source, Atmosph. Environ., 37, 2957–2966, 2003. Volkamer,~R., Sheehy,~P., Molina,~L T., and Molina,~M J.: Oxidative capacity of the Mexico City atmosphere – Part 1: A radical source perspective, Atmos. Chem. Phys., 10, 6969–6991, http://dx.doi.org/10.5194/acp-10-6969-2010doi:10.5194/acp-10-6969-2010, 2010. von Kuhlmann, R., Lawrence, M. G., Pöschl, U., and Crutzen, P. J.: Sensitivities in global scale modeling of isoprene, Atmos. Chem. Phys., 4, 1–17, http://dx.doi.org/10.5194/acp-4-1-2004doi:10.5194/acp-4-1-2004, 2004. Wong,~K W., Oh,~H.-J., Lefer,~B L., Rappenglück,~B., and Stutz,~J.: Vertical profiles of nitrous acid in the nocturnal urban atmosphere of Houston, TX, Atmos. Chem. Phys., 11, 3595–3609, http://dx.doi.org/10.5194/acp-11-3595-2011doi:10.5194/acp-11-3595-2011, 2011. Wong,~K W., Tsai,~C., Lefer,~B., Haman,~C., Grossberg,~N., Brune,~W H., Ren,~X., Luke,~W., and Stutz,~J.: Daytime HONO vertical gradients during SHARP 2009 in Houston, TX, Atmos. Chem. Phys., 12, 635–652, http://dx.doi.org/10.5194/acp-12-635-2012doi:10.5194/acp-12-635-2012, 2012. Yu,~Y., Galle,~B., Panday,~A., Hodson,~E., Prinn,~R., and Wang,~S.: Observations of high rates of NO<sub>2</sub>-HONO conversion in the nocturnal atmospheric boundary layer in Kathmandu, Nepal, Atmos. Chem. Phys., 9, 6401–6415, http://dx.doi.org/10.5194/acp-9-6401-2009doi:10.5194/acp-9-6401-2009, 2009 Zhang, N., Zhou, X., Shepson, P. B., Gao, H., Alaghmand, M., and Stirm B.: Aircraft measurement of HONO vertical profiles over a forested region, Geophys. Res. Lett., 36, L15820, http://dx.doi.org/10.1029/2009GL038999doi:10.1029/2009GL038999, 2009. Zhang, R., Sarwar, G., Fung, J. C. H., Lau, A. K. H., and Zhang, Y.: Impact of nitrous acid chemistry on air quality modeling results over the Pearl River Delta region, Atmos. Chem. Phys. Discuss., 11, 15075–15117, http://dx.doi.org/10.5194/acpd-11-15075-2011doi:10.5194/acpd-11-15075-2011, 2011. Zhang, N., Zhou, X., Bertman, S., Tang, D., Alaghmand, M., Shepson, P. B., and Carroll, M. A.: Measurements of ambient HONO concentrations and vertical HONO flux above a northern Michigan forest canopy, Atmos. Chem. Phys., 12, 8285–8296, http://dx.doi.org/10.5194/acp-12-8285-2012doi:10.5194/acp-12-8285-2012, 2012. Zhou, X., Gao, H., He, Y., Huang, G., Bertman, S. B., Civerolo, K., and Schwab, J.: Nitric Acid Photolysis on Surfaces in Low-NO$_\text x$ Environments: Significant Atmospheric Implications, Geophys. Res. Lett., 30, 2217, http://dx.doi.org/10.1029/2003GL018620doi:10.1029/2003GL018620, 2003. Zhou, X., Zhang, N., TerAvest, M., Tang, D., Hou, J., and Bertman, S., Alaghmand, M., Shepson, P. B., Carroll, M. A., Griffith, S., Dusanter, S., Stevens, P. S.: Nitric acid photolysis on forest canopy surface as a source for tropospheric nitrous acid, Nature Geosci. Lett., 4, 440–443, http://dx.doi.org/10.1038/ngeo1164doi:10.1038/ngeo1164, 2011. Zhou, X., Civerolo, K., Dai, H., Huang, G., Schwab, J. J., and Demerjian, K. L.: Summertime nitrous acid chemistry in the atmospheric boundary layer at a rural site in New York State, J. Geophys. Res., 107, 4590, http://dx.doi.org/10.1029/2001JD001539doi:10.1029/2001JD001539, 2002.