Articles | Volume 14, issue 6
Atmos. Chem. Phys., 14, 2805–2822, 2014

Special issue: Megapoli-Paris 2009/2010 campaign

Atmos. Chem. Phys., 14, 2805–2822, 2014

Research article 19 Mar 2014

Research article | 19 Mar 2014

Study of the unknown HONO daytime source at a European suburban site during the MEGAPOLI summer and winter field campaigns

V. Michoud1, A. Colomb2, A. Borbon1, K. Miet1, M. Beekmann1, M. Camredon1, B. Aumont1, S. Perrier1,3, P. Zapf1, G. Siour1, W. Ait-Helal1,4,5, C. Afif1,6, A. Kukui7,8, M. Furger9, J. C. Dupont10, M. Haeffelin10, and J. F. Doussin1 V. Michoud et al.
  • 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

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.

Final-revised paper