Airborne and ground-based measurements of aerosol optical depth of freshly emitted anthropogenic plumes in the Athabasca Oil Sands Region

• Published in: Atmospheric Chemistry and Physics
• Main Authors: Baibakov, Konstantin, LeBlanc, Samuel, Ranjbar, Keyvan, O'Neill, Norman T., Wolde, Mengistu, Redemann, Jens, Pistone, Kristina, Li, Shao-Meng, Liggio, John, Hayden, Katherine, Chan, Tak W., Wheeler, Michael J., Nichman, Leonid, Flynn, Connor, Johnson, Roy
• Format: Article in Journal/Newspaper
• Language: English
• Published: European Geosciences Union 2021
• Subjects: Canada; Fort McMurray
• Online Access: https://doi.org/10.5194/acp-21-10671-2021; https://nrc-publications.canada.ca/eng/view/ft/?id=e2fca141-49b3-45b2-bcc3-2c135c5b3903; https://nrc-publications.canada.ca/eng/view/object/?id=e2fca141-49b3-45b2-bcc3-2c135c5b3903; https://nrc-publications.canada.ca/fra/voir/objet/?id=e2fca141-49b3-45b2-bcc3-2c135c5b3903

In this work we report the airborne aerosol optical depth (AOD) from measurements within freshly emitted anthropogenic plumes arising from mining and processing operations in the Athabasca Oil Sands Region (AOSR) in the context of ground-based AERONET climatological daily averaged AODs at Fort McMurray (Alberta, Canada). During two flights on 9 and 18 June 2018, the NASA airborne 4STAR (Spectrometers for Sky-Scanning, Sun-Tracking Atmospheric Research) Sun photometer registered high fine-mode (FM, <1 µm) in-plume AODs of up to 0.4 and 0.9, respectively, in the vicinity of the plume source (<20 km). Particle composition shows that the plumes were associated with elevated concentrations of sulfates and ammonium. These high AODs significantly exceed climatological averages for June and were not captured by the nearby AERONET instrument (mean daily AODs of 0.10±0.01 and 0.07±0.02, maximum AOD of 0.12) due possibly to horizontal inhomogeneity of the plumes, plume dilution and winds which in certain cases were carrying the plume away from the ground-based instrument. The average 4STAR out-of-plume (background) AODs deviated only marginally from AERONET daily averaged values. While 4STAR AOD peaks were generally well correlated in time with peaks in the in situ-measured particle concentrations, we show that differences in particle size are the dominant factor in determining the 4STAR-derived AOD. During the two flights of 24 June and 5 July 2018 when plumes likely travelled distances of 60 km or more, the average 4STAR FM AOD increased by 0.01–0.02 over ∼50 km of downwind particle evolution, which was supported by the increases in layer AODs calculated from the in situ extinction measurements. Based on these observations as well as the increases in organic mass, we attribute the observed AOD increase, at least in part, to secondary organic aerosol formation. The in-plume and out-of-plume AODs for this second pair of flights, in contrast to clear differences in in situ optical and other measurements, were ...