1LISA, UMR-CNRS 7583, Université Paris Est Créteil (UPEC), Université Paris Diderot (UPD), Institut Pierre Simon Laplace (IPSL), Créteil, France
2LaMP, UMR-CNRS 6016, Clermont Université, Université Blaise Pascal, Aubière, France
3ISA, UMR-CNRS 5280, Université Lyon 1, ENS-Lyon, Villeurbanne, France
4Université Lille Nord de France, Lille, France
5Department of Chemistry and Environment, Ecole des Mines de Douai, Douai, France
6Centre d'Analyses et de Recherche, Faculty of sciences, Université Saint Joseph, Beirut, Lebanon
7LATMOS, UMR-CNRS 8190, Université de Versailles Saint Quentin, Université Pierre et Marie Curie, Guyancourt, France
8LPC2E, UMR-CNRS 6115, Orléans, France
9Laboratory of Atmospheric Chemistry, Paul Scherrer Institut, Villigen, Switzerland
10Institut Pierre Simon Laplace (IPSL), Palaiseau, France
Received: 12 Jul 2013 – Discussion started: 10 Sep 2013
Abstract. Nitrous acid measurements were carried out during the MEGAPOLI summer and winter field campaigns at SIRTA observatory in Paris surroundings. Highly variable HONO levels were observed during the campaigns, ranging from 10 ppt to 500 ppt in summer and from 10 ppt to 1.7 ppb in winter. Significant HONO mixing ratios have also been measured during daytime hours, comprised between some tenth of ppt and 200 ppt for the summer campaign and between few ppt and 1 ppb for the winter campaign. Ancillary measurements, such as NOx, O3, photolysis frequencies, meteorological parameters (pressure, temperature, relative humidity, wind speed and wind direction), black carbon concentration, total aerosol surface area, boundary layer height and soil moisture, were conducted during both campaigns. In addition, for the summer period, OH radical measurements were made with a CIMS (Chemical Ionisation Mass Spectrometer). This large dataset has been used to investigate the HONO budget in a suburban environment. To do so, calculations of HONO concentrations using PhotoStationary State (PSS) approach have been performed, for daytime hours. The comparison of these calculations with measured HONO concentrations revealed an underestimation of the calculations making evident a missing source term for both campaigns. This unknown HONO source exhibits a bell-shaped like average diurnal profile with a maximum around noon of approximately 0.7 ppb h−1 and 0.25 ppb h−1, during summer and winter respectively. This source is the main HONO source during daytime hours for both campaigns. In both cases, this source shows a slight positive correlation with J(NO2) and the product between J(NO2) and soil moisture. This original approach had, thus, indicated that this missing source is photolytic and might be heterogeneous occurring at ground surface and involving water content available on the ground.
Revised: 21 Jan 2014 – Accepted: 10 Feb 2014 – Published: 19 Mar 2014
Michoud, V., Colomb, A., Borbon, A., Miet, K., Beekmann, M., Camredon, M., Aumont, B., Perrier, S., Zapf, P., Siour, G., Ait-Helal, W., Afif, C., Kukui, A., Furger, M., Dupont, J. C., Haeffelin, M., and Doussin, J. F.: Study of the unknown HONO daytime source at a European suburban site during the MEGAPOLI summer and winter field campaigns, Atmos. Chem. Phys., 14, 2805-2822, doi:10.5194/acp-14-2805-2014, 2014.