Black carbon measurements

Black carbon (BC) is an important atmospheric constitute as an air pollutant and as a climate forcer. To our knowledge, field measurements of BC have not been reported over the South China Sea. Observation of light absorption coefficients (s_abs) and BC concentrations by Aethalometer were conducted on Yongxing Island in the South China Sea and at five continental sites in the Pearl River Delta (PRD) region, South China in two periods: period 1 dominated by South China Sea monsoon (16 May-20 June 2008 in rainy season) and period 2 dominated by northeast monsoon (12 December 2008- 8 January 2009 in dry season). At the oceanic site, the daily average BC concentrations varied from 0.28 to 2.14 μg m^-3 and variations of BC were small between the two periods (0.67 in the dry season sampling period and 0.54 μg m^-3 in the rainy season sampling period). Similarly, little difference in BC level was found at a rural site in PRD between the two sampling periods (2.88 in the dry season sampling period and 2.62 μg m^-3 in the rainy season sampling period). At the PRD urban sites, the daily average concentration of BC ranged from 1.56 to 37.9 μg m^-3, higher in the dry season sampling period (12.6 μg m^-3) and lower in the rainy season sampling period (6.4 μg m^-3). The observed average s_abs values in rainy vs. dry season sampling period are 119 vs. 62 Mm^-1 at the PRD urban sites, 29 vs. 26 Mm^-1 at the PRD background site, and 8.4 vs. 7.2 Mm^-1 at the marine site. At most PRD sites, BC was observed to have a diurnal pattern of higher concentrations at night and at the urban sites a small peak in the early morning rush hour.