Articles | Volume 16, issue 8
Atmos. Chem. Phys., 16, 4867–4883, 2016
Atmos. Chem. Phys., 16, 4867–4883, 2016

Research article 20 Apr 2016

Research article | 20 Apr 2016

Chemical and meteorological influences on the lifetime of NO3 at a semi-rural mountain site during PARADE

N. Sobanski1, M. J. Tang1,a, J. Thieser1, G. Schuster1, D. Pöhler2, H. Fischer1, W. Song1, C. Sauvage1, J. Williams1, J. Fachinger3, F. Berkes4,b, P. Hoor4, U. Platt2, J. Lelieveld1, and J. N. Crowley1 N. Sobanski et al.
  • 1Division of Atmospheric Chemistry, Max-Planck-Institut für Chemie, Mainz, Germany
  • 2Institute of Environmental Physics, University of Heidelberg, Heidelberg, Germany
  • 3Division of Particle Chemistry, Max-Planck-Institut für Chemie, Mainz, Germany
  • 4Institute for Atmospheric Physics, Johannes Gutenberg University Mainz, Mainz, Germany
  • apresent address: Chemistry Department, University of Iowa, Iowa City, USA
  • bpresent address: Institute of Energy and Climate, Forschungszentrum Jülich, Jülich, Germany

Abstract. Through measurements of NO2, O3 and NO3 during the PARADE campaign (PArticles and RAdicals, Diel observations of mEchanisms of oxidation) in the German Taunus mountains we derive nighttime steady-state lifetimes (τss) of NO3 and N2O5. During some nights, high NO3 (∼ 200 pptv) and N2O5 (∼ 1 ppbv) mixing ratios were associated with values of τss that exceeded 1 h for NO3 and 3 h for N2O5 near the ground. Such long boundary-layer lifetimes for NO3 and N2O5 are usually only encountered in very clean/unreactive air masses, whereas the PARADE measurement site is impacted by both biogenic emissions from the surrounding forest and anthropogenic emissions from the nearby urbanised/industrialised centres. Measurement of several trace gases which are reactive towards NO3 indicates that the inferred lifetimes are significantly longer than those calculated from the summed loss rate. Several potential causes for the apparently extended NO3 and N2O5 lifetimes are examined, including additional routes to formation of NO3 and the presence of a low-lying residual layer. Overall, the most likely cause of the anomalous lifetimes are related to the meteorological conditions, though additional NO3 formation due to reactions of Criegee intermediates may contribute.

Short summary
The nitrate radical (NO3) is an important nocturnal oxidant. By measuring NO3, its precursors (nitrogen dioxide and ozone) and several trace gases with which it reacts, we examined the chemical and meteorological factors influencing the lifetime of NO3 at a semi-rural mountain site. Unexpectedly long lifetimes, approaching 1 h, were observed on several nights and were associated with a low-lying residual layer. We discuss the role of other reactions that convert NO2 to NO3.
Final-revised paper