[PM2.5 Background Concentration at Different Directions in Beijing in 2013].

PM2.5, background concentration at different directions in 2013 in Beijing was analyzed combining the techniques of mathematical statistics, physical identification and numerical simulation (CMAQ4.7.1) as well as using monitoring data of six PM2.5 auto-monitoring sites and five meteorological sites in 2013. Results showed that background concentrations of PM2.5 at northwest, northeast, eastern, southeast, southern and southwest boundary sites were between 40.3 and 85.3 µg · m⁻³ in Beijing. From the lowest to the highest, PMPM2.5 background concentrations at different sites were: Miyun reservoir, Badaling, Donggaocun, Yufa, Yongledian and Liulihe. Background concentration of PM2.5 was the lowest under north wind, then under west wind, and significantly higher under south and east wind. Calculated PM2.5 background average concentrations were 6.5-27.9, 22.4-73.4, 67.2-91.7, 40.7-116.1 µg · m⁻³ respectively in different wind directions. Simulated PM2.5 background concentration showed a clear north-south gradient distribution and the surrounding area had a notable effect on the spatial distribution of PM2.5 background concentration in 2013 in Beijing.