为了探讨采暖期和非采暖期西安大气颗粒物水溶性组分的化学特征和来源， 分别于2005年冬季（2005年12月-2006年2月）和2006年夏季（6~8月）采集西安大气PM2.5和TSP样品， 分析其中Na+、 NH+4、 K+、 Mg2+、 Ca2+、 F-、 Cl-、 Br-、 NO-2、 NO-3和SO2-4共11种水溶性离子的浓度， 并对其季节特征和来源进行了研究。结果显示， 采暖期西安大气PM2.5和TSP中11种水溶性离子的平均浓度分别为53.2 μg·m-3和110.3 μg·m-3， 非采暖期分别为51.3 μg·m-3和89.3 μg·m-3。SO2-4、 NO-3和NH+4在PM2.5和TSP中均为最主要的离子组分， 浓度之和在采暖期分别占到PM2.5和TSP总离子浓度的78％和76％， 在非采暖期则占到88％和76％。PM2.5和TSP中， NH+4、 SO2-4和NO-3三者之间都有很好的相关性， 其在颗粒物中的主要结合形式为(NH4)2SO4、 NH4HSO4和NH4NO3。硫的转化率（SOR）和氮的转化率（NOR）在非采暖期明显大于采暖期， 揭示SO2-4和NO-3的形成机制为气相氧化， 主要受温度的控制。阴阳离子平衡和pH值测定的结果表明西安市大气PM2.5稍偏酸性， TSP为碱性， 无论是粗、 细粒子采暖期比非采暖期更偏酸性。对比10年前的研究结果， 显示西安市大气污染控制措施大大降低了采暖期气溶胶中二次组分的污染程度， 但主要污染排放源已逐渐由燃煤型向机动车排放转化。
Abstract
TSP and PM2.5samples were collected over Xi′an in winter (heating season) and summer (non heating season) to characterize the seasonal variations of water-soluble inorganic ions and to evaluate the effectiveness of the pollution controls during the past ten years. Mass concentrations of the water-soluble ions (Na+, NH+4, K+, Mg2+, Ca2+, F-, Cl-, Br-, NO-2, NO-3, and SO2-4) were measured for the total of 104 samples. The average concentration of the total 11 ions in PM2.5and TSP were 53.2 and110.3 g·m-3 in heating seasons, while they were 51.3and89.3 g m-3in non-heating seasons, respectively. SO2-4, NO-3,and NH+4were the majorions both in PM2.5and TSP; they occupied 78% and 76% of the total ions in PM2.5and TSP in heating seasons, and 88% and 76% in non-heating seasons. These three ions were mainly in the form of (NH4)2SO4, NH4HSO4and NH4NO3in aerosol particles. The sulfuroxidation ratio (SOR)and nitrogen oxidation ratio (NOR)in non heating season were higher than those in heating season, indicating SO2-4and NO-3were largely from the process of gas-phase photochemical reaction, and mainly influenced by ambient temperature. The ions balance between total cations and total anions and pH measurement showed that the airborne PM2.5at Xi′an was just a little acid, while TSP was a little alkaline. The heating season samples were more acid than the summer aerosol samples. Comparison with the data from ten years ago showed that the concentrationsof major three ions (SO2-4, NO-3and NH+4 ) decreased significantly,indicating that pollution controls in Xi′an were effective during the past ten years.On the other side, the emission of mobile source was prevailed to coal combustionand should be paid more attention in the near future.
关键词
大气颗粒物 /
水溶性离子 /
二次颗粒物 /
阴阳离子平衡
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Key words
Aerosol /
Water-soluble ions /
Secondary aerosol sp /
Ions balance
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