Near surface profiles of HONO: The vegetated surface as a source and a sink
P 3.7 in Ökosysteme: Funktion und Leistungen
The photolysis of HONO is an important primary OH radical source. The OH radical is the most important oxidizing agent, the so called “detergent” of the atmosphere. HONO formation pathways are still unclear. Nevertheless, the surface is proposed to be a major source of HONO due to heterogeneous photochemical formation or due to soil emissions from microbiological activity. Therefore, we measured gradients of HONO, NO, NO2 and O3 close to the surface.
We used an automated, programmable moving inlet to measure at three heights between 0.1 m and 1.6 m above the ground. HONO was measured with a long path absorption photometer (LOPAP), O3 by UV absorption and NO and NO2 by chemiluminescence with photolytic conversion of NO2. Additionally, profiles of temperature and relative humidity as well as leaf wetness and j(NO2) were measured. Measurements were conducted above a clearing and on the forest floor in the Fichtelgebirge Mountains.
Preliminary results are presented. For example, during the day the highest HONO concentrations were typically measured close to the ground, indicating emission of HONO from the surface. During the night, the lowest HONO concentrations were typically observed at the surface indicating deposition. The profile data will be analyzed with respect to light intensity, NO2 availability, atmospheric stability and surface wetness in order to elucidate the driving forces behind emission and deposition, respectively.