Nitrogen oxides and related compounds in north Europe. Atmospheric processes, deposition, monitoring and trends

Emissions of nitrogen oxides in Europe are causing a transboundary problem with respect to acid deposition as well as for the production of photochemical oxidants. Nitrate concentrations in precipitation over north Europe has doubled since the 50'ies, although the upward trend seems to have broken during the last decade. Nitrate contributes today as a mean for north Europe to 30-40 % of the acidity in rain. High concentrations of photochemical oxidants are frequently observed as a regional problem, where precursors emitted in one country may cause high concentrations in other countries. Although today's knowledge does not allow us to obtain accurate quantifications of the transpboundary fluxes of NOx, oxidants and oxidant precursors, existing results clearly show that oxidized nitrogen compounds and oxidants are internatonal air pollution problems wihich need to be handled through international agreements