LONG-TERM OBSERVATION OF NITRATE RADICALS AT THE TOR STATION, KAP-ARKONA (RUGEN)

Long-term observation of the trace gases NO2, ozone, and nitrate radic als (NO3) at a rural site in the Baltic Sea (near Kap Arkona, island R ugen) using differential optical absorption spectroscopy (DOAS) are pr esented here. The time series of these species cover more than 14 mont hs of data. Additionally, meteorological data were taken from the Deut scher Wetterdienst station at Kap Arkona. The average nighttime NO3 co ncentration was determined at 7.8 ppt. Maximum lifetimes of more than 5000 s were observed, but average NO3 lifetimes are close to 250 s. As nitrate radicals are expected to play an important role in the nonpho tochemical conversion of NOx to HNO3, long-term observations offer a k ey for investigation of possible sink mechanisms of NO3 molecules medi ated by both homogeneous and heterogeneous reactions. Analysis of the data shows that the NO3 lifetime is inversely proportional to the NO2 concentration, thus suggesting that the removal of N2O5 is actually th e dominating NO3 loss process. The mean N2O5 concentration from this l ong-term measurement was calculated at 1 ppb with an N2O5 lifetime bet ween 1000 s and 20000 s covering 90 % of the data.