This is comparable to previous studies of Cheng et al. [2006] conducted at the Hok Tsui of Hong Kong (2.4 mgm−3), and larger than the annual BC averages of the background or rural sites and less than those values of urban sites, which are located in other eastern Asia areas (Table 2). Throughout the sampling period, the lowest hourly BC value was 77.61 ng m−3 in autumn, which is quite close to the BC mass concentrations (50–120ngm−3) most frequently observed by Tang et al. [1999] using a similar instrument at Waliguan, a basic meteorological station located on the Tibet Plateau to reflect the background BC level of East Asia continent.