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 near Berlin, Germany, were performed using differential optical absorption spectroscopy (DOAS). Average nighttime NO3 levels were 4.6 ppt, while NO3 steady-state lifetimes (calculated from the NO2–O3 product and the NO3 concentration) varied between 5 s and 615 s with an average of 92 s. The long-term observations offered the possibility to study the importance of NO3 for the oxidation of VOCs (volatile organic compounds) and its contribution in the non-photochemical removal of NOx from the atmosphere in different seasons. Analysis of the data showed, that NO3 was depleted by both, reactions with VOCs and indirectly by loss of N2O5 on aerosol surfaces. A clear seasonal variation of the sink distribution was found. The VOC sink dominated during summer while indirect loss was of major importance during the winter months. The results are compared with former long-term campaigns of NO3 in the marine boundary layer.