Abstract Number: 689 Working Group: Remote and Regional Atmospheric Aerosol
Abstract The Arctic presents particular challenges when assessing aerosol direct and indirect climate forcing because of relatively sparse measurements in this region. Therefore, in situ surface measurements that characterize aerosols in detail, including their size distribution and optical properties, are needed to improve understanding of the composition and radiative properties of the Arctic atmosphere, particularly in the remote High Arctic.
The Polar Environment Atmospheric Research Laboratory (PEARL, 80°N 86°W) is a unique site for studying aerosols due to its location far above the Arctic Circle. At PEARL, year-round measurements of aerosol size distribution as well as of aerosol light scattering and absorption at 405 and 870 nm have been performed since 2016. During winter and springtime when the atmosphere at PEARL is impacted by Arctic Haze, scattering and absorption coefficients are much higher compared to the summer, with hourly total extinction reaching levels of 30 and 10 Mm-1 for 405 and 870 nm, respectively. Several intrinsic optical properties have been calculated from the measurements including SSA values as well as the scattering and absorption Angstrom exponents. Furthermore, the apparent real and imaginary components of the refractive index were retrieved using Mie theory, and their ranges (n = 1.65 – 1.81 and k = 0.002 – 0.012 at 405 nm) indicate very weak intrinsic absorption compared to elemental carbon.
A number of systematic relationships are found between the different optical properties. For example, the SSA at 405 nm is generally higher than that determined at 870 nm, with values ranging between 0.95 – 1 and 0.80 – 0.95, respectively. The higher scattering efficiency at the shorter wavelength is attributed to the relatively fine particle size of Arctic Haze aerosol. Lastly, comparisons of the in situ measurements to remote sensing and model data will also be discussed.