Changes in atmospheric nitrate deposition in Germany - An isotopic perspective

We investigated the isotopic composition of atmospheric NO3− deposition at a moderately polluted site in Western Europe over an annual cycle from December 2011 to November 2012. On average, we measured load-weighted δ15N values of +0.1 and +3.0‰ in wet and dry deposition, respectively. A comparison to source-specific N emission trends and to isotope data from the 1980s reveals distinct changes in δ15N-NO3− values: In contrast to the increasing relative importance of isotopically depleted natural NOx sources, we find an increase of isotope values in comparison to historical data. We explore the role of land-based N sources, because backward trajectories reveal a correlation of higher δ15N to air mass origin from industrialized areas. Nowadays isotopically enriched NOx of coal-fired power plants using selective catalytic converters and land-based vehicle emissions, which use same technology, are apparently the main driver of rising δ15N values in nitrate deposition.