Comparisons of aerosol nitrogen isotopic composition at two polluted coastal sites

Atmospheric fixed-nitrogen deposition can contribute to eutrophication in coastal and estuarine waters. Stable nitrogen isotope data can provide important information regarding the sources and processing of atmospheric fixed-nitrogen species and is thus important in controlling eutrophication. Size-segregated aerosol samples were collected from two coastal sites: Weybourne, England and Mace Head, Ireland and also aboard the RRS Challenger in the Eastern Atlantic Ocean. Aerosol concentrations of ammonium and nitrate were determined prior to delta N-15 isotopic analysis. For both species a significant difference in mean isotopic composition was seen between samples from Weybourne (+ 6 +/- 6 parts per thousand for ammonium and + 7 +/- 6 parts per thousand, for nitrate) and Mace Head and RRS Challenger campaigns (-9 +/- 8 parts per thousand, for ammonium and - 1 +/- 3 parts per thousand for nitrate). At each site a strong dependence of isotopic composition on the geographical origin of the sampled air mass was also observed. For aerosol ammonium, marine and terrestrially dominated samples were found to be isotopically distinct, perhaps reflecting the presence of oceanic sources of ammonia in addition to anthropogenic or natural terrestrial sources. Further distinctions were made within terrestrially dominated samples, possibly indicative of different types of animal husbandry regimes or other forms of anthropogenic activity. For aerosol nitrate, there was found to be generally less variation between samples at each site, although at Weybourne a significant difference was observed between the mean isotopic composition of samples originating from the northern UK (+ 15 +/- 3 parts per thousand) and that of those originating from the southern UK ( + 10 +/- 3 parts per thousand), suggesting that aerosol delta N-15 data might possibly facilitate source apportionment between NOx emissions from power stations and those from vehicle exhausts. The nitrate data also appeared to show seasonality with higher concentrations and lower delta N-15 values seen in the summer. (C) 2001 Elsevier Science Ltd. All rights reserved.