北京市城区单监测点PM_(2.5)质量浓度变化特征

VARIATIONALCHARACTERISTICS OF PM_(2.5) CONCENTRATION IN A MONITORING SITE IN BEIJING URBAN AREA

2009年在北京师范大学科技园内对PM2s质量浓度的连续监测结果表明，PM22.5质量浓度的年均值为55．2μg·m^-3日均值在1．2-325．9μg·m^-3之间变化，且频数分布呈现出明显的倾斜：大量的质量浓度值位于30-70μg·m^3之间；季节变化特征为冬季PM2.5污染水平明显高于其他季节；不同季节的日变化模式存在显著差异：整体上是冬季夜间质量浓度高于白天，夏季白天质量浓度高于夜晚，同时在各个季节下午16：00以后质量浓度都存在回升现象．

PM2.5 concentration was monitored continuously at The Science and Technology Park at Beijing Normal University in 2009. It was found that annual average PM2.5 concentration was 55.2μg·m^-3. The 24 h average concentrations ranged from 1.2 to 325.9 μg·m^-3 and frequency distributions for PM2.5 concentrations was highly skewed, with most of the values lying in the range from 30 to 70μg·m^-3. Pronounced seasonal variability was observed. PM2.5 concentration in winter was higher than in other seasons. Diurnal variation also changed with season： in winter, PM2.5 concentration at night was higher than in the day, but in summer this was reversed. In all seasons a concentration rebound after 4 PM was all observed.