Year: 2010
Abstract:
Oil sands comprise 30% of the world’s oil reserves and the crude oil reserves in Canada’s oil sands deposits are second only to Saudi Arabia. The extraction and processing of oil sands is much more challenging than for light sweet crude oils because of the high viscosity of the bitumen con- tained within the oil sands and because the bitumen is mixed with sand and contains chemical impurities such as sulphur. Despite these challenges, the importance of oil sands is in- creasing in the energy market. To our best knowledge this is the first peer-reviewed study to characterize volatile organic compounds (VOCs) emitted from Alberta’s oil sands mining sites. We present high-precision gas chromatography mea- surements of 76 speciated C2–C10 VOCs (alkanes, alkenes, alkynes, cycloalkanes, aromatics, monoterpenes, oxygenated hydrocarbons, halocarbons and sulphur compounds) in 17 boundary layer air samples collected over surface mining operations in northeast Alberta on 10 July 2008, using the NASA DC-8 airborne laboratory as a research platform. In addition to the VOCs, we present simultaneous measure- ments of CO2, CH4, CO, NO, NO2, NOy, O3 and SO2, which were measured in situ aboard the DC-8.
Carbon dioxide, CH4 , CO, NO, NO2 , NOy , SO2 and 53 VOCs (e.g., non-methane hydrocarbons, halocarbons, sul- phur species) showed clear statistical enhancements (1.1– 397×) over the oil sands compared to local background val-
Correspondence to: I. J. Simpson (isimpson@uci.edu)
ues and, with the exception of CO, were greater over the oil sands than at any other time during the flight. Twenty halo- carbons (e.g., CFCs, HFCs, halons, brominated species) ei- ther were not enhanced or were minimally enhanced (<10%) over the oil sands. Ozone levels remained low because of titration by NO, and three VOCs (propyne, furan, MTBE) remained below their 3 pptv detection limit throughout the flight. Based on their correlations with one another, the com- pounds emitted by the oil sands industry fell into two groups: (1) evaporative emissions from the oil sands and its prod- ucts and/or from the diluent used to lower the viscosity of the extracted bitumen (i.e., C4 –C9 alkanes, C5 –C6 cycloalka- nes, C6–C8 aromatics), together with CO; and (2) emissions associated with the mining effort, such as upgraders (i.e., CO2, CO, CH4, NO, NO2, NOy, SO2, C2–C4 alkanes, C2– C4 alkenes, C9 aromatics, short-lived solvents such as C2Cl4 and C2 HCl3 , and longer-lived species such as HCFC-22 and HCFC-142b). Prominent in the second group, SO2 and NO were remarkably enhanced over the oil sands, with maxi- mum mixing ratios of 38.7 ppbv and 5.0 ppbv, or 383× and 319× the local background, respectively. These SO2 lev- els are comparable to maximum values measured in heavily polluted megacities such as Mexico City and are attributed to coke combustion. By contrast, relatively poor correla- tions between CH4, ethane and propane suggest low levels of natural gas leakage despite its heavy use at the surface mining sites. Instead the elevated CH4 levels are attributed to methanogenic tailings pond emissions.
