Long-term observation of nitrate radicals in the continental boundary layer near Berlin

Long-term observations of the nitrate radical concentration and supporting parameters in the continental boundary layer at the rural site Lindenberg n ear Berlin, Germany, were performed using differential optical absorption s pectroscopy (DOAS). Average nighttime NO3 levels were 4.6ppt, while NO3 ste ady-state lifetimes (calculated from the NO2-O-3 product and the NO3 concen tration) varied between 5 s and 615 s with an average of 92 s. The long-ter m observations offered the possibility to study the importance of NO3 for t he oxidation of VOCs (volatile organic compounds) and its contribution in t he non-photochemical removal of NOx from the atmosphere in different season s. Analysis of the data showed, that NO3 was depleted by both, reactions wi th VOCs and indirectly by loss of N2O5 On aerosol surfaces. A clear seasona l variation of the sink distribution was found. The VOC sink dominated duri ng summer while indirect loss was of major importance during the winter mon ths. The results are compared with former long-term campaigns of NO3 in the marine boundary layer. (C) 2001 Elsevier Science Ltd. All rights reserved.