Compared with these measurements, herein the reference hourly Black Carbon of 7 mgm−3 for Tongyu strong events was close to the average Black Carbon level in the typical Chinese polluted urban regions, comparative to a visibility below 10 km estimated by the method of Deng et al. [2008]. Table 3 shows the Black Carbon events and corresponding mixing heights calculated from HYSPLIT4 model at maximal hourly Black Carbon concentrations during these events.