北京两次沙尘污染过程中PM2.5浓度变化特征

Variation of PM2.5 Concentration during Two Dust Pollution Events in Beijing

利用北京市空气质量监测数据和气象资料,对2013年2月28日和3月9日两次沙尘污染过程PM2.5(空气动力学当量直径小于等于2.5μm的颗粒物,即细颗粒物)、PM10(空气动力学当量直径小于等于10μm的颗粒物,即可吸入颗粒物)浓度及PM2.5浓度/PM10浓度比值的变化特征进行了分析,研究结果表明:(1)沙尘开始影响北京时,PM2.5与PM10浓度表现出反位相变化,PM10浓度在两次沙尘过程中2 h内分别上升50.8%与202.4%,最高达800μg m-3以上;PM2.5浓度分别下降58.3%与50.9%,直至下降至35μg m-3以下,PM2.5有明显改善现象。(2)虽然PM2.5浓度在沙尘到达前有缓升的迹象,但沙尘抵达后,PM2.5浓度持续快速下降,PM2.5浓度/PM10浓度比值由沙尘影响前的0.75以上降至0.25以下。沙尘影响前,PM2.5日均值均超过150μg m-3,北京地区处于重度污染水平。这说明沙尘来临前以人为污染为主,主要由细粒子"贡献",沙尘来临后的空气污染,主要由巨、大粒子的沙尘"贡献"。

Based on air quality automatic monitoring data and meteorological data, this study analyzed the variation of PM2.5, PM10, SO2, and NO2 during two dust weather cases that occurred in Beijing on 28 February and 9 March 2013. The results showed that：（1） Concentrations of PM2.5 and PM10 showed clearly opposite change characteristics when the dust arrived at Beijing： The PM10 concentration increased by 50.8% and 202.4% in two hours, respectively, with a maximum of over 800 μg m-3. On the contrary, the PM2.5 concentration decreased by 58.3% and 50.9%, respectively, both to lower than 35 μg m-3. The dust weather had a significant effect on reducing the concentration of PM2.5 in Beijing.（2） Although concentrations of PM2.5 rose slowly in a few hours before the dust arrived, the concentration of PM2.5 declined consistently during the dust arrival period. The PM2.5/PM10 ration dropped from above 0.75 to below 0.25. In both cases, the day before the dust day, daily concentrations of PM2.5 were greater than 150 μg m-3, and air quality was at a serious pollution level, implying that fine particulate matter contributed to the air pollution. After the arrival of the dust, air pollution was mainly caused by giant and large particulate matter.