Black carbon: Atmospheric concentrations and cloud water content measurements over southern Nova Scotia

Atmospheric black carbon concentrations have been measured in air and cloud water samples collected over southern Nova Scotia, Canada, during the North Atlantic Regional Experiment. The average black carbon atmospheric concentration found in continental air masses is 0.23 +/- 0.04 mu g/m(3) compared with 0.03 +/- 0.01 mu g/m(3) for maritime air. The concentrations found in the 1- to 3- km layer are higher than those below 1 km, suggesting that most of the black carbon is not of local origin. About 9% of black carbon was in the form of an internal mixture inside cloud droplets. The average black carbon content of cloud water was about 40 mu g/kg. The average black carbon to non-sea-salt SO4 mass mixing ratio was found to be between 0.02 and 0.04.