A seasonal variation of hourly BC was obvious, with the highest monthly average in April (4.16 mgm) and the lowest in July (1.43 mgm−3) (Figure 2). The average BC 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 BC in October (15.4 mgm−3) was about 55 times the lowest value in May (0.28 mgm−3). This distribution of
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