A seasonal variation of hourly Black Carbon was obvious, with the highest monthly average in April (4.16 mgm−3) and the lowest in July (1.43 mgm−3) (Figure 2). The average Black Caebon concentration during spring (3.1 mg/m−3) was about 1.7 times that of summer (1.83 mgm−3), and the highest daily average Black Carbon in October (15.4 mgm−3) was about 55 times the lowest value in May (0.28 mgm−3).