Understanding the Primary Emissions and Secondary Formation of Gaseous Organic Acids in the Oil Sands Region of Alberta, Canada

Abstract

<p><strong>Abstract.</strong> 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 tonnes day<sup>−1</sup> of low molecular weight organic acids, dominated by C<sub>1</sub>–C<sub>5</sub> 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 measured previously (≈ 20 tonnes day<sup>−1</sup>), for which there are reporting thresholds. Conversely, photochemical production of gaseous organic acids significantly exceeded the primary sources, with formation rates up to ≈ 184 tonnes day<sup>−1</sup> downwind of the oil sands facilities. The formation and evolution of organic acids from a Lagrangian flight were modeled with a box model, incorporating a detailed hydrocarbon reaction mechanism extracted from the Master Chemical Mechanism (v 3.3). 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 oils sands operations, suggest the existence of significant missing oil sands related secondary sources/precursor emissions and/or an incomplete mechanistic and quantitative understanding of how they are processed in the atmosphere.</p>

Spaceborne Measurements of Formic and Acetic Acids: A Global View of the Regional Sources

“…Moreover, whereas the C(O)O /RO reactions yielding COOH dominate in clean and remote environments, in polluted conditions (high NO concentration) C(O)O primarily reacts with NO to produce methyl peroxy radical ( O ) and peroxyacyl nitrates. Although large direct COOH emissions have been reported locally from fossil fuel and biofuel burning (e.g., Kawamura et al, ; Liggio et al, ), altogether the primary and secondary anthropogenic sources are estimated not to contribute significantly to the HCOOH and COOH burden (Khan et al, ; Müller et al, ; Paulot et al, ), leaving the indirect biogenic source as the main known driver throughout the year.…”

Estimates of Exceedances of Critical Loads for Acidifying Deposition in Alberta and Saskatchewan

“…TERRA makes use of aircraft flux data 10 and mass conservation equations to estimate emissions from facilities, and was shown to produce SO 2 emissions estimates which were within 5% of direct within-stack estimates from Continuous Emissions Monitoring. The algorithm has more recently been used to estimate the emissions fluxes of intermediate volatility organic compounds (Liggio et al, 2016), volatile organic compounds and the primary emissions of gaseous organic acids from these facilities (Liggio et al, 2017). 5…”

Theoretical Study on Criegee Intermediate’s Role in Ozonolysis of Acrylic Acid

“…50 Reaction between CH 2 OO and acrylic acid could be a major sink of concentration of CH 2 OO in some regions, with a large emission of carboxylic acid. 51 Besides, not only for acrylic acid, fast reaction with CH 2 OO should be characteristic of carboxylic acid because of the existence of the carboxylic moiety. From organic acid concentration 50 and other common species in the atmosphere along with rate coefficients, 52 it can be seen that, to CH 2 OO, acrylic acid, and more generally carboxylic acids, are potent scavengers.…”

“…It holds true not only for acrylic acid but also for other organic acids which possess a carboxylic group. It is noteworthy that human activities including industrial production, bonfires, and fireworks have a strong correlation with emission of acid and formation of related SOA, [13][14][15]51,55 showing CH 2 OO's weaved involvement in atmospheric chemistry. More information is still needed to validate the mechanism experimentally and atmospherically and to raise attention toward the possibly overlooked formation source of SOA.…”