In Situ Measurements of the Mixing State and Light-Scattering Properties of Black Carbon in the Troposphere and Lower Stratosphere.

Measurements were made of light-scattering from individual particles containing black carbon (BC) using a single particle soot photometer (SP2) integrated on board a NASA WB-57F high altitude research aircraft. The measurements were made during January and February 2006 at altitudes from near the surface to 19 km and at latitudes from 40^{circ}N to the equator. The BC mass of each particle was measured over the range ~0.1 - 0.6 μm BC volume equivalent diameter. The mixing state of each particle was inferred from light-scattering characteristics, with a detection limit equivalent to a ~40 nm coating of dry sulfate. We observed strongly contrasting mixing states for BC in the lower stratosphere versus the troposphere. Mie calculations were used to derive the coating thickness, single-scatter albedo, and enhanced light absorption for individual particles. These results provide important observations of the mixing state of black carbon particles in the tropical troposphere and lower stratosphere and, hence, represent important constraints on BC removal rates and lifetimes in global aerosol models.