上海冬春季PM2.5中不挥发和半挥发颗粒物的浓度特征

微量振荡天平法广泛的应用于我国PM2.5的监测,该方法50℃的采样加热温度会导致PM2.5中半挥发颗粒物的损失, 而仅可获得PM2.5中的不挥发颗粒物的质量浓度,因此,PM2.5浓度的实际测值会偏低.微量振荡天平和膜动态测量联用技术可同时获得PM2.5中不挥发和半挥发颗粒物的质量浓度,本研究利用该技术于2011年12月~2012年4月在上海城郊开展了PM2.5中不挥发和半挥发颗粒物的连续观测,并对其浓度特征进行了分析.结果表明:上海冬春季大气PM2.5中半挥发性颗粒物占有较高比重,平均浓度比率为18.91%;PM2.5中半挥发颗粒物主要来自NH4NO3,在NH4NO3浓度较高的地区,PM2.5的监测应考虑半挥发颗粒物的损失;半挥发性颗粒物补偿前后的PM2.5浓度间有着较好的线性关系,在一定数据质量目标下,可由未补偿的浓度推算补偿后的PM2.5浓度.

Characteristics of non-volatile and semi-volatile particulate matters in PM2.5 in Shanghai during winter and spring

The tapered element oscillating microbalance (TEOM) instruments are widely used to measure the concentration of PM2.5 in China. It is found that only non-volatile particulate matters can be measured by TEOM method, while the semi-volatile particulate matters are lost by increased sampling temperature at 50℃. Thus, the PM2.5 concentrations are undermeasured. Currently, a new method of combining TEOM with FDMS (Filter Dynamic Measurement System) was developed and applied to measure both the non-volatile and the semi-volatile particulate matters in PM2.5. In this paper, the non-volatile and semi-volatile fractions in PM2.5 were measured in the suburban aera of Shanghai from Dec. 2011 to Apr. 2012. The results showed that the semi-volatile fraction accounted for 18.91% in PM2.5. NH4NO3 is an overwhelming component in the semi-volatile fraction in mega cities, therefore, additional compensation of PM2.5 measurement must be concerned in this regime. Based on the well linear correlation between compensated PM2.5 concentration and uncompensated PM2.5 concentration, the compensated concentration of PM2.5 could be calculated by the measured uncompensated PM2.5.