北京城区PM_(2.5)中有机碳和元素碳的变化特征

Characteristics of Organic Carbon and Elemental Carbon in PM_(2.5) in Urban of Beijing

为了了解北京城区大气细颗粒物(PM2.5)中有机碳(OC)和元素碳(EC)的浓度水平与季节变化特征,2013年5月、8月、10月和2014年1月分季节在北京城区进行了PM2.5和PM2.5中OC、EC的连续监测。在监测期间,PM2.5质量浓度平均值为86.8μg/m3,PM2.5中OC的平均浓度为15.46μg/m3,占PM2.5的17.8%;EC的平均浓度为2.88μg/m3,占PM2.5的3.3%。北京城区的PM2.5和OC、EC随季节变化明显,冬季最高,秋季大于春季,夏季最低。其中秋、冬季的OC、EC浓度的日变化有着明显的白天低、傍晚前后逐渐升高、在午夜出现峰值的特点。通过一次重污染过程分析发现,静稳、高湿的气象条件使PM2.5、OC、EC的浓度都有着显著地增加。对OC、EC相关分析显示,冬季两者的相关性最高。而且OC/EC的比值都大于2.0,说明北京存在着一定的二次污染。

In order to understand the concentration and the season characteristics of organic carbon and elemental carbon in PMz~ in urban of Beijing, OC, EC and PM2.5 were continuously monitored in May, August, October, 2013 and in January, 2014. During the monitoring, average concentration of PM25 was 86.8 μg/m3, average concentration of OC in PM2.5 was 15.46 μg/m3, accounting for 17.8% in PM2.5; average concentration of EC in PM2.5 was 2.88 μg/m3, accounting for 3.3% in PM2.5. The season variation of the concentration of PM2.5, OC, EC were clear, with the highest concentration in winter and the lowest in summer, and the concentration in autumn higher than in spring. The daily variation of the concentration was lower in the daytime, increasing at nightfall, with the highest in the midnight during autumn and winter. Through the process of the heavy air pollution, the concentration was clearly increasing in the low wind and high humidity. The correlation between OC and EC was better in winter. And the ratios of OC/EC were all larger than 2.0, indicating the existence of the secondary pollution in Beijing.