Vertical profiles of light absorption and scattering associated with black carbon particle fractions in the springtime Arctic above 79° N

• Published in: Atmospheric Chemistry and Physics
• Main Authors: W. R. Leaitch, J. K. Kodros, M. D. Willis, S. Hanna, H. Schulz, E. Andrews, H. Bozem, J. Burkart, P. Hoor, F. Kolonjari, J. A. Ogren, S. Sharma, M. Si, K. von Salzen, A. K. Bertram, A. Herber, J. P. D. Abbatt, J. R. Pierce
• Format: Article in Journal/Newspaper
• Language: English
• Published: Copernicus Publications 2020
• Subjects: Physics; QC1-999; Chemistry; QD1-999; Arctic; Nunavut; albedo; black carbon; Canadian Archipelago
• Online Access: https://doi.org/10.5194/acp-20-10545-2020; https://doaj.org/article/d3ea359ec1ad4c66b3e04b6e8e9b1aa5

Despite the potential importance of black carbon (BC) for radiative forcing of the Arctic atmosphere, vertically resolved measurements of the particle light scattering coefficient ( σ sp ) and light absorption coefficient ( σ ap ) in the springtime Arctic atmosphere are infrequent, especially measurements at latitudes at or above 80 ∘ N. Here, relationships among vertically distributed aerosol optical properties ( σ ap , σ sp and single scattering albedo or SSA), particle microphysics and particle chemistry are examined for a region of the Canadian archipelago between 79.9 and 83.4 ∘ N from near the surface to 500 hPa . Airborne data collected during April 2015 are combined with ground-based observations from the observatory at Alert, Nunavut and simulations from the Goddard Earth Observing System (GEOS) model, GEOS-Chem, coupled with the TwO-Moment Aerosol Sectional (TOMAS) model (collectively GEOS-Chem–TOMAS; Kodros et al., 2018) to further our knowledge of the effects of BC on light absorption in the Arctic troposphere. The results are constrained for σ sp less than 15 Mm −1 , which represent 98 % of the observed σ sp , because the single scattering albedo (SSA) has a tendency to be lower at lower σ sp , resulting in a larger relative contribution to Arctic warming. At 18.4 m 2 g −1 , the average BC mass absorption coefficient (MAC) from the combined airborne and Alert observations is substantially higher than the two averaged modelled MAC values (13.6 and 9.1 m 2 g −1 ) for two different internal mixing assumptions, the latter of which is based on previous observations. The higher observed MAC value may be explained by an underestimation of BC, the presence of small amounts of dust and/or possible differences in BC microphysics and morphologies between the observations and model. In comparing the observations and simulations, we present σ ap and SSA, as measured, and σ ap ∕2 and the corresponding SSA to encompass the lower modelled MAC that is more consistent with accepted MAC values. Median values of the ...