Abstract Number: 1019 Working Group: Remote/Regional Atmospheric Aerosol
Abstract This study presents long-term observations of aerosol size distributions for both coarse and fine modes as well as of aerosol light scattering and absorption that are ongoing at the Polar Environment Atmospheric Research Laboratory (PEARL) in the Canadian High Arctic (80N, 86W) since summer 2016. A variety of field measurements are utilised including a scanning mobility particle sizer, an optical particle counter, and two Photoacoustic Extinctiometers. The scattering and absorption coefficients are measured at 405 nm and 870 nm, and from these measurements a number of derived parameters are calculated such as aerosol single scattering albedo (SSA), the scattering and absorption angstrom exponents as well as black carbon concentration. The measurements of the aerosol scattering and absorption coefficients are also compared against the coefficient values calculated using Mie theory and the measured aerosol size distribution in an optical closure study.
As expected a strong seasonal variation in scattering and absorption is observed with higher scattering and absorption coefficient values during the wintertime Arctic Haze. Average SSA values of 0.96 are observed for 405 nm and 870 nm during the 2016 winter. The scattering angstrom exponent (SAE) varied between values of 1 and 4, wherease the absorption angstrom exponent (AAE) showed relatively little variation with an average value of 0.83 during the same period. The changes in the SAE are likely due to changes in particle size, with periods of low SAE resulting from long-range transported black carbon and periods of high SAE suggesting larger coated particles, possibly containing black carbon as well. Furthermore, a preliminary optical closure study has shown that the measured scattering coefficient is in agreement with the values calculated using Mie Theory, the measured size distributions, and an assumed value for the refractive index.
Finally, the optical properties determined from the surface measurements will be compared against sun photometer measurements to understand the relationship between the surface and columnar aerosol optical properties. The measurements at PEARL provide a unique combination of surface and columnar data sets on aerosols in the High Arctic, a region where such measurements are scarce despite the impact of aerosols on the climate of the Arctic.