沙尘天气对兰州市PM10中主要水溶性离子的影响

利用在线监测仪器MARGA在兰州大学盘旋路校区对兰州市大气PM10中水溶性离子进行监测,监测期间(2011-04-01~2011-06-30)有15 d出现沙尘天气.兰州市PM10中主要水溶性离子物种为Ca2+、SO2-4和NO-3.扬沙天气期间NO-3和NH+4的浓度比非沙尘期间低,说明沙尘天气对当地人为源所排放污染物具有清除作用.沙尘天气期间,作为土壤污染源标识物的Mg2+、Na+和Ca2+离子都有明显增加,Na+和Mg2+相关系数为0.520,Na+和Ca2+相关系数为0.659,Mg2+和Ca2+相关系数为0.671,而非沙尘天气期间三者的相关系数并不高,Na+和Mg2+相关系数为0.065,Na+和Ca2+相关系数为0.131,Mg2+和Ca2+相关系数为0.163,说明沙尘天气期间三者之间具有相同的污染源,主要来自于土壤风沙尘,而非沙尘天气期间三者来源不同.Cl-的浓度在扬沙天气明显高于浮尘和非沙尘天气期间,说明外来的土壤风沙尘是Cl-的主要来源.

Effect of Sand Dust Weather on Major Water-soluble Ions in PM10 in Lanzhou, China

The major water-soluble ions (Ca²⁺, NH₄⁺, Mg²⁺, K⁺, Na⁺, SO₄^2-, NO₃^- and Cl^-) in PM₁₀ at 1-h interval were measured by an online analyzer for monitoring of Aerosols and Gases(MARGA) at the campus of Lanzhou University, from April 1 to June 30, 2011. There were 15 days of dust weather during the monitoring period. The main water-soluble ions in PM₁₀ were Ca²⁺, SO₄^2- and NO₃^-. The concentration of NO₃^- and NH₄⁺ decreased during blowing sand weather comparing with non-dust, this phenomenon showed that the dust weather had the function of eliminating the local anthropogenic emissions. As the soil pollution marker,the concentration of Mg²⁺, Na⁺ and Ca²⁺ increased during dust weather comparing with non-dust. The correlation coefficients between Na⁺ and Mg²⁺, Na⁺ and Ca²⁺, Mg²⁺ and Ca²⁺ during dust weather were 0.520, 0.659 and 0.671, respectively. The similar correlation coefficients indicated that some fraction of these species was derived from the same sources, such as soil dust. The correlation coefficients between Na⁺ and Mg²⁺, Na⁺ and Ca²⁺, Mg²⁺ and Ca²⁺ during non-dust weather were not strong, only 0.065, 0.131 and 0.163, respectively. The low correlation coefficients indicated that these species were derived from different sources. The mass concentration of Cl^- in the dust weather was significantly higher than that of floating dust and non dust, indicating that soil dust was the main source of Cl^-.