Measurement and analysis of black carbon aerosol in Xi'an

Black carbon (BC) aerosol was measured using an Aethalometer at Xi'an station for 10 months in 2004. Every 5 min BC concentrations ranged from 0.2 to 124.5 mg / m3. Average daily BC concentrations were found to be the highest in December 15 with 63.1 mg / m3, the lowest in July 22 with 2.0 mg / m3. The average monthly BC concentrations were from 9.0 mg / m3 in April to 21.8 mg / m3 in November. The weekly patterns of BC concentrations appeared to be dual-peak distributions. The value of BC in autumn and winter was higher than that of spring and summer. The BC concentrations became higher on Monday and Friday. Significant reduction in BC values was observed on Saturday. The diurnal variation pattern of BC was similar for all seasons. BC concentrations found to be the highest at 23:00 h in spring, summer and autumn, at 21:00 h in winter. Low value has been observed in afternoon. BC concentrations are high during morning (06:00 to 09:00 h) and evening hours (19:00 to 23:00 h) compared with afternoon hours. Compared with BC concentrations of other cities and background stations in the world, BC over Xi'an atmosphere was higher. Motor vehicle exhaust, coal combustion emissions and biomass burning contributed to the highest BC concentrations in Xi'an.