Long-range transport and deposition of acidic nitrogen species in north-west Europe

The mechanisms of the long-range transport and deposition of acidic nitrogen compounds over north-west Europe are not yet well understood. Aerosol nitrate concentrations have been steadily rising in southern England1 over the past three decades, as have the nitrate concentrations in precipitation at almost all sites in northwest Europe, including the most remote2,3. The life cycle of acidic nitrogen compounds potentially involves a wide range of trace constituents including nitric oxide (NO), nitrogen dioxide (NO2), gaseous nitric acid (HNO3), higher nitrogen oxides (such as N2O5), nitrate aerosol and nitrate in precipitation. Here we show that a simple model, incorporating an assumed life cycle of nitrogen-containing trace gases and the known NO sources, can account for much of the nitrate in rain observed over north-west Europe.