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Atmospheric Chemistry and Physics An interactive open-access journal of the European Geosciences Union
Atmos. Chem. Phys., 17, 8411-8427, 2017
https://doi.org/10.5194/acp-17-8411-2017
© Author(s) 2017. This work is distributed under
the Creative Commons Attribution 3.0 License.
Research article
11 Jul 2017
Understanding the primary emissions and secondary formation of gaseous organic acids in the oil sands region of Alberta, Canada
John Liggio1, Samar G. Moussa1, Jeremy Wentzell1, Andrea Darlington1, Peter Liu1, Amy Leithead1, Katherine Hayden1, Jason O'Brien1, Richard L. Mittermeier1, Ralf Staebler1, Mengistu Wolde2, and Shao-Meng Li1 1Air Quality Research Division, Environment and Climate Change Canada, Toronto, Ontario, M3H 5T4, Canada
2National Research Council Canada, Flight Research Laboratory, Ottawa, K1A 0R6, Canada
Abstract. Organic acids are known to be emitted from combustion processes and are key photochemical products of biogenic and anthropogenic precursors. Despite their multiple environmental impacts, such as on acid deposition and human–ecosystem health, little is known regarding their emission magnitudes or detailed chemical formation mechanisms. In the current work, airborne measurements of 18 gas-phase low-molecular-weight organic acids were made in the summer of 2013 over the oil sands region of Alberta, Canada, an area of intense unconventional oil extraction. The data from these measurements were used in conjunction with emission retrieval algorithms to derive the total and speciated primary organic acid emission rates, as well as secondary formation rates downwind of oil sands operations. The results of the analysis indicate that approximately 12 t day−1 of low-molecular-weight organic acids, dominated by C1–C5 acids, were emitted directly from off-road diesel vehicles within open pit mines. Although there are no specific reporting requirements for primary organic acids, the measured emissions were similar in magnitude to primary oxygenated hydrocarbon emissions, for which there are reporting thresholds, measured previously ( ≈  20 t day−1). Conversely, photochemical production of gaseous organic acids significantly exceeded the primary sources, with formation rates of up to  ≈  184 t day−1 downwind of the oil sands facilities. The formation and evolution of organic acids from a Lagrangian flight were modelled with a box model, incorporating a detailed hydrocarbon reaction mechanism extracted from the Master Chemical Mechanism (v3.3). Despite evidence of significant secondary organic acid formation, the explicit chemical box model largely underestimated their formation in the oil sands plumes, accounting for 39, 46, 26, and 23 % of the measured formic, acetic, acrylic, and propionic acids respectively and with little contributions from biogenic VOC precursors. The model results, together with an examination of the carbon mass balance between the organic acids formed and the primary VOCs emitted from oil sands operations, suggest the existence of significant missing secondary sources and precursor emissions related to oil sands and/or an incomplete mechanistic and quantitative understanding of how they are processed in the atmosphere.

Citation: Liggio, J., Moussa, S. G., Wentzell, J., Darlington, A., Liu, P., Leithead, A., Hayden, K., O'Brien, J., Mittermeier, R. L., Staebler, R., Wolde, M., and Li, S.-M.: Understanding the primary emissions and secondary formation of gaseous organic acids in the oil sands region of Alberta, Canada, Atmos. Chem. Phys., 17, 8411-8427, https://doi.org/10.5194/acp-17-8411-2017, 2017.
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Short summary
The emission and formation of gaseous organic acids from the oil sands industry in Canada is explored through aircraft measurements directly over and downwind wind of industrial facilities. Results demonstrated that the formation of organic acids through atmospheric chemical reactions dominated over the direct emissions from mining activities but could not be explicitly modeled. The results highlight the need for improved understanding of photochemical mechanisms leading to these species.
The emission and formation of gaseous organic acids from the oil sands industry in Canada is...
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