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The Athabasca deposit in Alberta is the largest oil sand in the world and is a powerful source of Canadian energy. Over the last decade a lot attention has been paid to the environmental impacts of oil sands production. Primary emissions associated with oil sands activities have been the focus of past research but less is known about the reaction products of these emissions to the atmosphere. In the SOCCAR Seminar held on September 14, Dr. Liggio, a research scientist at Environment and Climate Change Canada’s Air Quality Research Division, presented his research on the formation of organic acidity and secondary organic aerosol from oil sands activities.
All particulate matter emitted into the atmosphere eventually becomes oxidized. Volatile organic compounds (VOC) become oxidized to form products such as organic acids. VOC can also form condensable products called secondary organic aerosols (SOA).
SOA makeup a major fraction of particulate matter in many places. The effect of SOA on ecosystem health is unclear but they are known to contribute to urban and regional air quality problems. On the other hand, organic acids contribute to rain acidity and some have been linked to the ecosystem impacts on marine invertebrates or even on humans.
Oil sands are a mixture of sand, water, clay and a type of oil called bitumen. It’s mined from the ground and the bitumen is separated out, processed, and eventually sold.
Dr. Liggio and his team conducted an aircraft campaign in August 2013 over the Athabasca oil sands in Alberta. The data collected were used to understand the transport and transformation of primary pollutants from oil sand sources to downwind areas that were hundreds of kilometers away. They observed the oil sand emissions consist mostly of two plume types: either VOC rich or SO2 rich. Bitumen SOA dominated the plumes and that was associated with the intermediate volatility organic compounds (IVOC) emitted into the atmosphere from open-pit mining activities. The researchers calculated a significantly quantity, 45-84 tonnes/day, of SOA was being formed as a result of the oil sands activities. In fact, the mass of SOA being formed is similar to estimates for Canada’s largest city (Toronto).
In addition to SOA from oil sand facilities, organic acids were observed in the plumes downwind of the mine. It’s known that organic acids are also primary emissions from oil sands facilities resulting from hauling trucks and other diesel machinery. The primary organic acid emission rates from mine trucks were dominated by C1-C5 acids such as acetic and formic acid. But it was observed that the secondary formation rates were 30 to 40 times larger than primary emission rates from trucks. Dr. Liggio believes the secondary formation of organic acids is largely contributed by the carbon emitted from VOC that’s converted into organic acids.
HCNO is another organic acid that was measured as part of the airship campaign. It is a known toxic acid that has been associated with an inflammatory response from smoking and leads to cardiovascular disease. But it can also be formed from gas and diesel combustion as a primary emission or secondary formation from diesel exhaust oxidation, so it’s an important emission to analyze for oil sands activities. The team did measure HCNO in the oil sand plumes. Primary formation of HCNO in the oil sands operations from trucks are found to be larger than the on road primary emissions for the entire Canadian mobile fleet of gasoline and diesel vehicles. More secondary emissions of HCNO were observed in the downwind plume than the secondary HNCO from the entire Canadian mobile fleet of gasoline and diesel vehicles. More importantly, Dr. Liggio observed that there are 20 to 30 times more secondary formation than primary emissions. He believes there is something happening in the oil sands causing it to form a lot faster than just oxidizing diesel exhaust in the lab.
From the airship campaign, the team found that SOA formation from oil sands is one of the bigger sources in North America and is mostly attributed to the bitumen vapors released during the mining process. Both primary emission and secondary formation of organic acids are observed. However, organic acid formation is poorly modeled and contributions from IVOC are likely missing from model. Therefore the emission of IVOC needs to be incorporated into air quality models and SOA should be assessed when current and future oil sand projects involve extracting bitumen.