Airborne Mysteries

Art Courtesy of Kara Tao.

Oil production is estimated to be responsible for around fifteen percent of total global energy-related emissions. From extraction to refining to consumption, various stages of oil production are heavily associated with air pollution. But our ability to estimate organic carbon emissions from these processes may be threatened by the emergence of more unconventional oil sources in recent decades. Two of these sources, heavy oil and bitumen deposits, are projected to account for about forty percent of oil production by the year 2040.

In a recent paper published in Science, a team of researchers from Yale and Environment and Climate Change Canada, a department of the Canadian government, examined the magnitude and impact of traditionally unmonitored gases on total organic carbon emissions. 

Addressing Overlooked Air Pollutants

Organic carbon emissions, or gaseous organic compounds, refer to substances containing carbon and hydrogen that are released into the atmosphere. Historically, studies on carbon emissions have focused on volatile organic compounds (VOCs), a subset of organic carbon emissions that have short- and long-term adverse effects on human health and the environment. “These compounds pose both environmental and human health risks,” said Lexie Gardner (YC ’23), a co-author of the study and environmental engineer at CDM Smith. Short-term health effects include respiratory irritation, headaches, dizziness, and fatigue, while more long-term effects include cancer, organ damage, and neurological effects.

While certain subsets are typically the focus of monitoring and industry reporting, many types of emissions go unmonitored—including emissions that still contribute greatly to air pollution. These compounds include intermediate-volatility organic compounds (IVOCs) and semivolatile organic compounds (SVOCs). Their volatility, or tendency to evaporate at a given temperature, influences their emissions and abundance in the atmosphere, though they all undergo chemical reactions in the atmosphere that affect air quality. Up until now, they have largely gone unmonitored compared to VOCs. “There are opportunities for improvement in emissions reporting,” said Drew Gentner, an associate professor of chemical and environmental engineering at Yale and senior author of the study.

Studying unmonitored gases is particularly important because the reported concentration of emissions helps dictate policy on environmental regulations. Air pollution contributes to the worsening effects of climate change, which has direct ramifications on legislation. “Organic carbon emissions encompass a wide range of species with a diverse range of sizes and functionalities,” said Megan He (YC ’22), the lead author of the study and a current graduate student at Harvard University. “For typical research and reporting purposes, it is hard to measure all of these individual species together,” He said.

Underreporting by Canadian Oil Sands Operations

Oil sands are a critical contributor to the majority of Canadian oil production, particularly in the Athabasca oil sands regions in northern Alberta, which make up about two-thirds of Canadian oil production. Oil sands provide a substantial source of unconventional petroleum, which refers to compounds of hydrogens and carbons (hydrocarbons) extracted from unconventional sources, such as tight reservoirs and oil sands themselves. Special extraction and processing techniques are used to extract these compounds from unconventional sources compared to conventional ones. Oil sands, often incorrectly known as tar sands, are composed of bitumen—a heavier version of crude oil—sand, and clay. The bitumen is separated from the sand and the clay and is then refined into various petroleum products. However, the extraction and processing techniques pose several environmental challenges, one of which is their impact on air quality.

The researchers were interested in using new measurements to quantify the total carbon emissions and compare those values to estimates reported by the industry on the Athabasca oil sands. They performed both airborne measurements and supplementary laboratory experiments. 

The first experiment they did was to collect air samples and later analyze their contents. The researchers used an aircraft to measure the total carbon emissions in the Athabasca oil sands. A total of thirty flights were conducted flying both upwind and downwind near five different facilities, some of which were for surface mining and others for in situ mining. Surface mining consists of the removal of overlying rock or soil to access the valuable minerals underneath and is ideal when the minerals are located close to the surface. In situ mining consists of extracting minerals directly from their location without the removal of overlying rock or soil. The five facilities were Syncrude Mildred Lake, Suncor, Canadian Natural Resources, Imperial Kearl Lake, and MJP Petroleum Corporation. 

“The aircrafts were equipped with instruments capable of analyzing gas-phase organic pollutants and were supplemented by samples taken in the field,” Gardner said. After the samples were analyzed, the researchers found that the total reported annual carbon emissions were underestimated by about 1,900 percent to over 6,300 percent, depending on the respective facility. The researchers focused on the three facilities that had the highest carbon emissions, which were Syncrude Mildred Lake, Suncor, and Canadian Natural Resources. Of the three facilities, Syncrude Mildred Lake was found to have the highest percentage difference between estimated carbon emissions and reported values (6,324 percent), while Canadian Natural Resources had the lowest difference (1,922 percent). 

“The benefit of a total gas-phase organic carbon measurement is that you convert all of the complex mixture of organic carbon compounds to carbon dioxide with a catalyst and just measure the produced carbon dioxide,” Gentner said. This means that instead of individually quantifying each organic carbon compound present in the atmosphere, the researchers were able to directly measure carbon content, streamlining the measurement process. Consequently, IVOCs and SVOCs are just as much a part of the equation as VOCs normally are. However, this conversion makes it difficult to attribute respective measurements to the specific organic carbon compounds. Thus, additional measurements were necessary to conduct the experiments and distinguish between different organic compounds. In addition, based on observations from the aircraft, the researchers determined that non-combustion-related sources largely contribute to the emissions. “[This] is likely contributed to by a range of on-site sources across the lifecycle of oil sands extraction [and] processing,” He said. 

Supplementary experiments were conducted to determine whether mature fine tailings also contributed to the total organic carbon observed during the flights. Mature fine tailings are structures that are built into the earth and house mining waste from oil sands. This waste consists of a mixture of particles, such as sand, clay, and silt, which are difficult to separate from wastewater and serve as a persistent environmental pollutant. Over time, off-gassing emissions—emissions released under normal environmental conditions—were measured. The magnitude and chemical composition of emissions were determined, and the researchers demonstrated that mature fine tailings contribute to the total organic carbon observed.

“The collection of aircraft and laboratory measurements in the study demonstrates the importance of considering life-cycle-wide emissions, spanning from mining through waste management and disposal,” Gentner said.

Limitations of Aircraft-Based Emissions Monitoring

These new aircraft-based measurements elucidated stark differences between the total reported annual carbon emissions compared to the total annual carbon emission estimates, calling for a need to better monitor the impact of oil production on our climate. However, there are a few limitations to this study. Methane is responsible for approximately sixteen percent of global emissions, making it the second-largest contributor to climate warming after carbon dioxide. Despite being one of the most abundant greenhouse gases, it was excluded from the study. “Other research by Environment and Climate Change Canada has specifically examined methane [and carbon dioxide] emissions,” He said. Thus, the researchers decided to specifically focus on VOCs, IVOCs, and SVOCs, which methane does not fall under.

In addition, it may be difficult to use aircraft-based measurements in other cases beyond Canada’s oil sands due to sensitivity. “Generally speaking, aircraft-based measurements are challenging since you have an array of sensitive instrumentation on the aircraft that you are preparing for each flight,” Gentner said. The researchers were careful to adequately calibrate and monitor each flight to prevent any inaccurate measurements.

Improving Reporting of Total Organic Carbon Emissions

Ultimately, the findings from this study can help inform future policy. The researchers identified challenges with reporting and monitoring diverse gaseous organic compounds but also highlighted the necessity of obtaining comprehensive emissions data. With these new methods for quantifying total carbon emissions beyond VOCs, policymakers will be able to determine which programs must be implemented. As we seek to mitigate worsening climate change, it is imperative to have accurate measurements of total carbon emissions to create accurate, effective, and crucial environmental policies and regulations across the globe.