Absorption Properties of Arctic Aerosol

The Arctic region is highly sensitive to global climate change. Aerosols, especially their absorption properties, have a significant potential to affect climate forcing. Accurate knowledge of aerosol absorption is critical to derive a complete set of aerosol optical properties from remote radiance measurements. We present airborne observations obtained during the NOAA-sponsored Aerosol Radiation and Cloud Processes affecting Arctic Climate (ARCPAC) campaign conducted in April 2008. The observations were made with a Particle Soot Absorption Photometer (PSAP) and a Single-Particle Soot Photometer (SP2) on the NOAA WP-3D research aircraft in flights from Fairbanks, Alaska. PSAP measures ensemble aerosol absorption and the SP2 selectively measures the refractory black carbon (rBC) content of individual particles. The correlation of PSAP and derived SP2 absorption at 530 nm is highly linear over a range of values from background to higher levels associated with biomass burning plumes. PSAP absorption on average is 23% larger than SP2 values, thereby providing strong evidence that in the Arctic 2008 springtime the dominant aerosol absorber is refractory black carbon at 530 nm and longer wavelengths. In addition, the SP2 observations show that the majority of BC mass resides in only a small subset of particles in the total aerosol population. This suggests that the retrieval algorithms for the remote sensing of atmospheric absorption such as those used by AERONET may need significant revision.