ATMOCHEM - PHOTOchemical Formation of Nitrous Acid in the Atmosphere (PHOTONA)

• Applicant: Privatdozent Dr. Jörg Kleffmann
• Subject Area: Atmospheric Science
• Term: from 2008 to 2013
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 83105133

Nitrous Acid (HONO) has attracted significant attention during the last few years since recent field measurements have demonstrated that the photolysis of HONO can be the dominant source of OH radicals in the lower atmosphere. The OH radical is responsible for the degradation of most air pollutants and for the formation of harmful photooxidants. Thus, the identification and quantification of the sources of HONO are of major importance. To explain unexpected high daytime concentrations of HONO, different photochemical sources have been proposed. However, the exact origin and the magnitude of HONO fluxes over irradiated rural and urban surfaces are still open questions, which have to be solved to understand and quantify the oxidation capacity of the atmosphere.In the proposed project, these questions are aimed to be answered by the integration of selected laboratory, field and modelling studies. In the laboratory studies, different photochemical sources of HONO will be investigated in photoreactors by the help of very sensitive and selective instrumentation to enable the simulation of atmospheric relevant conditions. In the field studies, the daytime source strength of HONO will be quantified over irradiated surfaces by the help of a mixed gradient / eddy-covariance technique at a field site near Paris (INRA/Grignon), which is already used for flux measurements of NOx and O3 since two years. The HONO fluxes will be parameterized for different types of surfaces (e.g. pure soil and crop) as a function of measured variables (solar intensity, NO2, nitrate, etc.). In addition, daytime gradients measurements in the altitude range 10-200 m will be performed under urban conditions at the meteorological tower at Forschungszentrum Karlsruhe to better quantification the impact of the HONO photolysis on the radical budget for an extended altitude range. The results from the lab and field studies - including data from recent other studies - will be used to improve existing box, 1-D and 3-D models with the focus on the better description and quantification of the oxidation capacity of the boundary layer. The outcome of the project will have an essential impact on the understanding of the photochemistry of the lower atmosphere.

• DFG Programme: Research Grants
• International Connection: France
• Participating Persons: Dr. Yuri Bedjanian; Dr. Pierre Cellier