天津市高校夏季道路扬尘PM2.5中水溶性离子污染特征及来源

为研究天津市高校道路扬尘PM_2.5中水溶性离子的污染特征、来源及校内外差异，于2018年7—8月采集天津市9所高校道路扬尘样品，用离子色谱法对其中8种水溶性离子（Ca²⁺、K⁺、Mg²⁺、Na⁺、Cl^-、NH₄⁺、NO₃^-、SO₄^2-）进行分析.结果显示：①水溶性离子占PM_2.5的11.65%，PM_2.5中占比大于1%的离子有Ca²⁺和SO₄^2-，其中Ca²⁺最多，占到总水溶性无机离子的65.75%；②入校道路离子含量（12.76%）稍高于校内道路（11.11%），其中8种离子含量的差异均无统计学意义；CE/AE（阴阳离子当量浓度比）值为9.59（远大于1），PM_2.5呈较强碱性；③NH₄⁺与SO₄^2-、NO₃^-主要以（NH₄）₂SO₄和NH₄NO₃的形态结合；④NO₃^-/SO₄^2-的比值为0.45，说明固定源的贡献更大；⑤天津市高校道路扬尘PM_2.5主要来源于海盐粒子、燃煤、机动车尾气、建筑水泥尘等.

Characteristics and sources of water-soluble ions in road dust PM2.5 during summer in university campuses of Tianjin

In order to study the characteristics and sources of water-soluble ion pollution in road dust PM_2.5 at university campuses in Tianjin, and to compare the differences of concentrations inside and outside universities, road dust samples were collected at 9 universities in Tianjin from July to August of 2018, and 8 water-soluble ions (including Ca²⁺, K⁺, Mg²⁺, Na⁺, Cl^-, NH₄⁺, NO₃^-, SO₄^2-) were measured by ion chromatography. The water-soluble ions accounted for 11.65% of PM_2.5. Ions with a ratio of >1% in PM_2.5 were Ca²⁺ and SO₄^2-, of which Ca²⁺ was the most, accounting for 65.75% of total water-soluble inorganic ions. The median concentration of total ions for entrance roads (12.76%) was slightly higher than those on-campus roads (11.11%), and there were no significant differences for 8 ions between entrance roads and on-campus roads. The ratio of anion to cation equivalent concentration was 9.59 (much higher than 1), which showed that PM_2.5 in road dust was strong alkaline. NH₄⁺ combined with SO₄^2- and NO₃^- mainly in the form of (NH₄)₂SO₄ and NH₄NO₃. The ratio of NO₃^-/SO₄^2- was 0.45, indicating that the contribution of stationary sources was greater than mobile exhaust. Road dust PM_2.5 in campuses was mainly from the sea salt particles, coal combustion, motor vehicle exhaust and cement dust.