中文摘要：

通过对广州2007年夏季雨水硝酸盐δ15的研究，讨论了广州地区雨水硝酸盐的主要来源及与之有关的大气化学演变过程。雨水硝酸盐占δ15N的变化趋势与N2O5含量的相似。暗示雨水硝酸盐δ15N与氮氧化合物的大气化学过程之间存在某种联系。白天雨水硝酸盐δ15N值偏低，与OH自由基氧化NOx生成硝酸盐的“白天反应”为主要反应相一致；18：00以后硝酸盐δ15N值呈升高趋势，则与N2O5累积的“夜间反应”成为主导反应相一致。因“白天反应”生成的HNO3的δ15N值受同位素分馏影响较小，白天雨水硝酸盐占δ15N值更能准确反映大气NOx的来源。白天雨水硝酸盐占δ15N平均值为2．5‰±2．1‰，表明除火力发电厂和机动车尾气排放来源外，雷电以及海源对大气NOx可能也有潜在贡献。

英文摘要：

Sources and related atmospheric evolution processes of rainwater nitrate were studied using the nitrate δ15N values during summertime in Guangzhou. The rainwater samples were collected from July to September, 2007. The variation pattern of rainwater nitrate δ15N was similar to that of atmospheric N2O5, implying probable relationship between them. During daytime 615N was relatively low, concurrent with the daytime nitric acid formation via NO2 oxidation by OH radical; during the nighttime nitrate δ15N elevated to higher values, consistent with the nighttime nitric acid formation via hydrolysis of N2O5 from NO2 oxidation by O3. Due to limited isotope fraetionation during daytime nitric acid formation, daytime rainwater nitrate δ15N values in Guangzhou could approximate that of atmospheric NO x. The mean value of daytime rainwater nitrate δ15N measured in the present study was 2.5‰±2.1‰, lower than the overall mean value of 4.8‰± 3.2‰. Apart from vehicle exhausts and coal-fired power stations, lightening and maritime sources might also be potential contributors of rainwater nitrate in Guangzhou.