Black carbon aerosol mass concentrations over Ahmedabad, an urban location in western India: Comparison with urban sites in Asia, Europe, Canada, and the United States

Black carbon (BC) aerosol mass concentrations measured using an aethalometer at Ahmedabad, an urban location in western India, from September 2003 to June 2005 are analyzed. BC mass concentrations are found to show diurnal and seasonal variations. Diurnal evolution in BC is marked with two peaks, one in the morning hours, just after the sunrise, and the other in the late evening hours. The peaks occur due to fumigation effect of boundary layer, gradual increase in the anthropogenic activities, and rush hour traffic. January BC values are about a factor of 5 higher than July mass concentrations. During winter the surface boundary layer is shallow resulting in trapping of pollutants in a lesser volume which leads to higher BC concentrations. In July an increase in boundary layer height, surface temperature, convective activity, and rainfall result in lower BC values. BC mass concentrations are about 0.8 μ g m −3 in July 2004 (southwest monsoon), while BC was higher than 5 μ g m −3 in January 2004 (northeast monsoon). Ahmedabad BC mass concentrations are higher than those measured over central, western India and Hyderabad, an urban city in south India during a land campaign in February 2004. BC values measured over Ahmedabad are found to be higher than those measured over various locations representing different environments in Europe. Seasonal variations are less pronounced in urban locations in Europe. BC mass concentrations at east St. Louis, Illinois, an urban site are found to be less than 2 μ g m −3 during September 2003 to June 2005, with less pronounced seasonal variations. BC mass concentrations at various land locations in India, Beijing, and Seoul are higher than those measured over various locations in Europe, Canada, and the United States.