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 delta N-15 values of +0.1 and +3.0 parts per thousand 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 delta N-15-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 delta N-15 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 delta N-15 values in nitrate deposition. (C) 2014 The Authors. Published by Elsevier Ltd.