Heating rates and surface dimming due to black carbon aerosol absorption associated with a major U.S. city

Abstract

In situ airborne measurements of actinic flux and the mass and mixing state of individual refractory black carbon (BC) particles were made in the lower troposphere around a major U.S. metropolitan area. These data were used to estimate atmospheric heating rates and surface dimming due to absorption of solar radiation by refractory BC. Direct absorption by ozone is also calculated and averages 10% of that of BC below 4 km but becomes dominant above this altitude. Variability in BC absorption is large due to source variability and clouds. Average BC heating rates are much smaller than those associated with BC and other absorbing aerosol components in global hotspot regions. These results, which are specific to refractory BC. absorption, will help determine the value of short-term climate-change mitigation strategies involving BC emission reductions. They may also be used to estimate refractory BC contributions to total aerosol absorption Copyright 2009 by the American Geophysical Union.