Shipboard measurements of concentrations and properties of carbonaceous aerosols during ACE-2

Mass concentrations of total, organic and black carbon were derived by anal yzing the super-micron and submicron aerosol fractions of shipboard collect ed samples in the eastern Atlantic Ocean as part of the second Aerosol Char acterization Experiment (ACE-2). These analyses were complemented by experi ments intended to estimate the water-soluble fraction of the submicron carb onaceous material. Our results can be summarized as follows. Depending on t he sample, between 35% and 80% of total aerosol carbon is associated with t he submicron fraction. Total submicron carbon was well correlated with blac k carbon, a unique tracer for incomplete combustion. These correlations and the approximately constant total to black carbon ratios, suggest that the majority of submicron total carbon is of primary combustion derived origin. No systematic relationship between total submicron aerosol carbon and sulf ate concentrations was found. Sulfate concentrations were, with a few excep tions, significantly higher than total carbon. Our experiments have demonst rated that water exposure removed between 36% and 72% of total carbon from the front filter, suggesting that a substantial fraction of the total submi cron aerosol organic carbon is water-soluble. An unexpected result of this study is that water exposure of filter samples caused substantial removal o f, nominally insoluble, submicron black carbon. Possible reasons for this o bservation are discussed.