Articles | Volume 16, issue 22
Atmos. Chem. Phys., 16, 14475–14493, 2016
Atmos. Chem. Phys., 16, 14475–14493, 2016

Research article 22 Nov 2016

Research article | 22 Nov 2016

Daytime formation of nitrous acid at a coastal remote site in Cyprus indicating a common ground source of atmospheric HONO and NO

Hannah Meusel1, Uwe Kuhn1, Andreas Reiffs2, Chinmay Mallik2, Hartwig Harder2, Monica Martinez2, Jan Schuladen2, Birger Bohn3, Uwe Parchatka2, John N. Crowley2, Horst Fischer2, Laura Tomsche2, Anna Novelli2,3, Thorsten Hoffmann4, Ruud H. H. Janssen2, Oscar Hartogensis5, Michael Pikridas6, Mihalis Vrekoussis6,7,8, Efstratios Bourtsoukidis2, Bettina Weber1, Jos Lelieveld2, Jonathan Williams2, Ulrich Pöschl1, Yafang Cheng1, and Hang Su1 Hannah Meusel et al.
  • 1Max Planck Institute for Chemistry, Multiphase Chemistry Department, Mainz, Germany
  • 2Max Planck Institute for Chemistry, Atmospheric Chemistry Department, Mainz, Germany
  • 3Institute for Energy and Climate Research (IEK-8), Research Center Jülich, Jülich, Germany
  • 4Johannes Gutenberg University, Inorganic and Analytical Chemistry, Mainz, Germany
  • 5Wageningen University and Research Center, Meteorology and Air Quality, Wageningen, the Netherlands
  • 6Cyprus Institute, Energy, Environment and Water Research Center, Nicosia, Cyprus
  • 7Institute of Environmental Physics and Remote Sensing – IUP, University of Bremen, Bremen, Germany
  • 8Center of Marine Environmental Sciences – MARUM, University of Bremen, Bremen, Germany

Abstract. Characterization of daytime sources of nitrous acid (HONO) is crucial to understand atmospheric oxidation and radical cycling in the planetary boundary layer. HONO and numerous other atmospheric trace constituents were measured on the Mediterranean island of Cyprus during the CYPHEX (CYprus PHotochemical EXperiment) campaign in summer 2014. Average volume mixing ratios of HONO were 35 pptv (±25 pptv) with a HONO ∕ NOx ratio of 0.33, which was considerably higher than reported for most other rural and urban regions. Diel profiles of HONO showed peak values in the late morning (60 ± 28 pptv around 09:00 local time) and persistently high mixing ratios during daytime (45 ± 18 pptv), indicating that the photolytic loss of HONO is compensated by a strong daytime source. Budget analyses revealed unidentified sources producing up to 3.4  ×  106 molecules cm−3 s−1 of HONO and up to 2.0  ×  107 molecules cm−3 s−1 NO. Under humid conditions (relative humidity  >  70 %), the source strengths of HONO and NO exhibited a close linear correlation (R2 = 0.72), suggesting a common source that may be attributable to emissions from microbial communities on soil surfaces.

Short summary
There are many studies which show discrepancies between modeled and measured nitrous acid (HONO, precursor of OH radical) in the troposphere but with no satisfactory explanation. Ideal conditions to study the unknown sources of HONO were found on Cyprus, a remote Mediterranean island. Budget analysis of trace gas measurements indicates a common source of NO and HONO, which is not related to anthropogenic activity and is most likely derived from biologic activity in soils and subsequent emission.
Final-revised paper