天津市PM2.5中氮含量及同位素的昼夜及季节变化

为研究天津市大气气溶胶中氮的来源，分析了2016年夏、冬两季昼夜采集的细颗粒物气溶胶（PM_2.5）中无机离子浓度和氮同位素组成（δ¹⁵N）.结果显示：天津市冬季平均PM_2.5质量浓度（207 μg/m³）远高于夏季（40.1 μg/m³），冬季PM_2.5的δ¹⁵N值（+5.1‰）低于夏季（+10.7‰），即夏季PM_2.5较冬季更富集¹⁵N；夏季PM_2.5中NH₄⁺的平均浓度高于c（NO₃^–），但是冬季NO₃^–浓度最高，其次是c（NH₄⁺）>c（SO₄^2–）；此外，通过对比昼夜样品，夏季PM_2.5中氮含量和氮同位素组成在昼夜均表现出明显差异，而冬季不明显.结果表明，天津市夏季气溶胶中含氮化合物在昼夜受海陆风的影响，即白天受海洋气溶胶影响较大而夜间则为陆源气溶胶物质影响，然而冬季受东亚季风的影响削弱了海陆风对海陆间大气气溶胶的交换作用，且在冬季化石燃料燃烧源氮贡献较大.

Diurnal and seasonal variations of nitrogen contents and isotopic composition of total nitrogen in PM2.5 in Tianjin

In order to understand the sources of nitrogen in atmospheric aerosols in Tianjin, the concentration of inorganic ions and nitrogen isotopic composition (δ¹⁵N) of total nitrogen (TN) in fine aerosols (PM_2.5) collected on day and night basis in summer and winter of 2016 were studied. The results showed that the average mass concentration of PM_2.5 in winter (207μg/m³) was much higher than that in summer (40.1μg/m³), and the δ¹⁵N value of TN in PM_2.5in winter (+5.1‰) was lower than that in summer (+10.7‰), with high enrichment of ¹⁵N in the summer. The average concentration of NH₄⁺ in PM_2.5 in summer was higher than that of NO₃^- (c(NO₃^-)), whereas in winter, it was opposite:c(NO₃^-) was higher than c(NH₄⁺), followed by c(SO₄^2-). In addition, both nitrogen contents and δ¹⁵N of TN in PM_2.5 showed significant differences between day and night in summer, but not in winter. The results demonstrated that the nitrogen loading in summer aerosols in Tianjin was significantly affected by the sea-land circulation, that is, with ocean aerosols during the day and terrestrial aerosols at night. However, East Asian monsoon in winter weakened the exchange effect of sea-land circulation, while the contribution of fossil fuel combustion source to nitrogen was more significant in winter.