Characterization of trace gases measured over Alberta oil sands mining operations: 76 speciated C<sub>2</sub>–C<sub>10</sub> volatile organic compounds (VOCs), CO<sub>2</sub>, CH<sub>4</sub>, CO, NO, NO<sub>2</sub>, NO<sub>y</sub>, O<sub>3</sub> and SO<sub>2</sub>
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...
| Main Authors: | , , , , , , , , , , , , |
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| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2010-12-01
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| Series: | Atmospheric Chemistry and Physics |
| Online Access: | http://www.atmos-chem-phys.net/10/11931/2010/acp-10-11931-2010.pdf |
| Summary: | 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 contained 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 increasing 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 measurements of 76
speciated C<sub>2</sub>–C<sub>10</sub> 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 measurements of CO<sub>2</sub>, CH<sub>4</sub>, CO, NO, NO<sub>2</sub>,
NO<sub>y</sub>, O<sub>3</sub> and SO<sub>2</sub>, which were measured in situ aboard the DC-8.
<br><br>
Carbon dioxide, CH<sub>4</sub>, CO, NO, NO<sub>2</sub>, NO<sub>y</sub>, SO<sub>2</sub> and 53 VOCs
(e.g., non-methane hydrocarbons, halocarbons, sulphur species) showed clear
statistical enhancements (1.1–397×) over the oil sands compared to
local background values and, with the exception of CO, were greater over the
oil sands than at any other time during the flight. Twenty halocarbons
(e.g., CFCs, HFCs, halons, brominated species) either 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 compounds emitted by the
oil sands industry fell into two groups: (1) evaporative emissions from the
oil sands and its products and/or from the diluent used to lower the
viscosity of the extracted bitumen (i.e., C<sub>4</sub>–C<sub>9</sub> alkanes,
C<sub>5</sub>–C<sub>6</sub> cycloalkanes, C<sub>6</sub>–C<sub>8</sub> aromatics), together with CO;
and (2) emissions associated with the mining effort, such as upgraders
(i.e., CO<sub>2</sub>, CO, CH<sub>4</sub>, NO, NO<sub>2</sub>, NO<sub>y</sub>, SO<sub>2</sub>,
C<sub>2</sub>–C<sub>4</sub> alkanes, C<sub>2</sub>–C<sub>4</sub> alkenes, C<sub>9</sub> aromatics,
short-lived solvents such as C<sub>2</sub>Cl<sub>4</sub> and C<sub>2</sub>HCl<sub>3</sub>, and
longer-lived species such as HCFC-22 and HCFC-142b). Prominent in the second
group, SO<sub>2</sub> and NO were remarkably enhanced over the oil sands, with
maximum mixing ratios of 38.7 ppbv and 5.0 ppbv, or 383× and
319× the local background, respectively. These SO<sub>2</sub> levels are
comparable to maximum values measured in heavily polluted megacities such as
Mexico City and are attributed to coke combustion. By contrast, relatively
poor correlations between CH<sub>4</sub>, ethane and propane suggest low levels of
natural gas leakage despite its heavy use at the surface mining sites.
Instead the elevated CH<sub>4</sub> levels are attributed to methanogenic tailings
pond emissions.
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In addition to the emission of many trace gases, the natural drawdown of OCS
by vegetation was absent above the surface mining operations, presumably
because of the widespread land disturbance. Unexpectedly, the mixing ratios
of α-pinene and β-pinene were much greater over the oil sands (up to 217 pptv
and 610 pptv, respectively) than over vegetation in the background boundary
layer (20±7 pptv and 84±24 pptv, respectively), and the
pinenes correlated well with several industrial tracers that were elevated
in the oil sands plumes. Because so few independent measurements from the
oil sands mining industry exist, this study provides an important initial
characterization of trace gas emissions from oil sands surface mining
operations. |
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| ISSN: | 1680-7316 1680-7324 |