Characterization of fine particulate black carbon in Guangzhou, a megacity of South China

Continuous measurement of fine particulate black carbon (BC) was conducted at an urban site of Guangzhou in South China from December 2007 to December 2008. The daily average BC concentrations ranged from 0.6 to 20.5 mu g m(-3), with an average value of 4.7 mu g m(-3), which was substantially higher than those observed in the urban areas of other developed countries. Diurnal fluctuations of BC were marked with two peaks, one in the morning rush hour (08:00 LT) and the other in the late evening hour (21:00-22:00 LT), while the lowest BC concentrations were observed in the afternoon. Ambient BC concentrations displayed significant seasonal and diurnal variations with higher values in winter and spring, followed by lower concentrations during autumn and summer. Wind speed, wind direction and temperature were important meteorological factors that affected BC concentrations. A clearly negative correlation (r=-0.50, p<0.01) between BC concentrations and wind speed was found during the study period. A specific investigation was conducted to determine the relationship between optical BC and thermal-optical-reflectance elemental carbon (TOR EC) in distinct seasons. Although significant correlations between BC and EC were obtained (r>0.92, p<0.01), the regression slopes (Delta BC/Delta EC) slightly deviated from each other with values of 0.79, 1.18, and 0.81 in winter, spring and summer, respectively, possibly due to the distinct mixing states and source variations in different seasons. The calculated experimental attenuation coefficient showed a higher value (19.3 m(2) g(-1)) in Guangzhou than the one recommended for typical Aethalometer measurements.