Talk, Atmospheric Transport and Chemistry in Forest Ecosystems, Thurnau: 2009-10-05 - 2009-10-08
Nitrous acid (HONO) has been measured in the atmosphere for about 30 years now. But formation pathways are still controversial especially for daytime formation. Night time formation is believed to occur via heterogeneous hydrolysis of NO2 forming HONO and HNO3. Thus wetted ground surfaces should contribute a lot to HONO formation, but also act as sinks at high relative humidity when liquid films are formed. We have performed simultaneous HNO2 measurements in and above a tall spruce forest canopy using two long path absorption photometers (LOPAPs) at a field site located in the Fichtelgebirge mountains in north-eastern Bavaria, Germany (50°09’N, 11°52’E, 775 m above sea level) during intensive operating periods of the EGER- Project. Coupling regimes according to Thomas and Foken  were calculated from measurements of sonic anemometers. Diurnal cycles of HONO and concentration differences from above canopy (24.5 m) and close to the forest floor (0.5 m) are discussed in view of coupling (of the forest to the atmosphere) and the interdependency of HONO and humidity.