SEASONAL-VARIATION OF N-15-N-14 RATIOS IN ATMOSPHERIC NITRATE SPECIES

Nitrate in rain sampled in moderately polluted areas at Julich/Germany and Ahrensburg/Germany, as well as in a rural area at Deuselbach/Germany and in a coastal area at Le Conquet/France, shows a pronounced seasonal variation in its N-15/N-14 ratio with lower data in summer (delta-N-15 = - (5 +/- 1) parts per thousand; mean between the stations) than in winter (delta-N-15 = (0 +/- 2) parts per thousand)). Particulate nitrate trapped in low- and high-volume sampling at Julich shows a similar seasonal N-15/N-14 variation (delta-N-15 of about +3 parts per thousand +7 parts per thousand in summer and winter, respectively); the absolute data however differ from those in the rain samples. Nitric acid vapour, on the other hand, exhibits nearly constant N-15/N-14 data over the seasons (delta-N-15 = - (2-3) parts per thousand). The data are discussed considering isotope exchange reactions and kinetic fractionations involved in transformations of atmospheric oxidized nitrogen species. Full explanations must await further measurements.