Residential heating fuel use is the largest contributor to primary sulfate pollution in Fairbanks’ winter air, according to research conducted as part of a 2022 international community science program.
Authors of a recent research article, published in ACS ES&T Air, write that the results, along with other results from the program, will help air quality managers decide which improvement methods to use. This information could also benefit other high-latitude urban areas in winter.
William Simpson, a professor at the University of Alaska Fairbanks, an atmospheric and environmental chemist and co-author of the paper, said the research predicts that a reduction in airborne primary sulfates is likely.
“The finding that most sulfate particles are directly emitted is good news as primary sulfate is expected to decline alongside fuel oil sulfur reductions that began in September 2022,” he said.
Previous studies have identified residential heating oil as the primary source of sulfate particles in Fairbanks’ air, but have not clarified whether this occurs through direct emission from residential heating, called primary sulfate, or through atmospheric chemical reactions after exhaust, called secondary sulfate.
The new research also found that most primary sulfate particles are less than 0.7 microns in diameter. One micron is equivalent to one thousandth of a millimeter. One millimeter is the thickness of 10 sheets of standard photocopier paper.
Particles 2.5 microns or smaller, known as PM2.5, have been shown to cause respiratory and heart disease among residents of cold communities with poor air dispersion. Particles smaller than 0.7 microns pose a greater risk to human health because they can penetrate deeper into the body.
The paper’s authors write that primary sulfate made up, on average, 50 to 74 percent of the total sulfate present in Fairbanks’ winter air during the 2022 research season. Secondary sulfate made up the remainder.
The paper’s 23 co-authors include three from the University of Alaska Fairbanks: Simpson and Associate Professor Jingqiu Mao, also an atmospheric/environmental chemist; and Meeta Cesler-Maloney, graduate student in atmospheric sciences. Simpson and Mao are affiliated with the UAF Geophysical Institute and the UAF College of Natural Sciences and Mathematics.
“The biggest finding is that primary sulfate makes up the majority of sulfate, especially since it is so abundant in the smaller size category,” said Allison Moon, lead author of the paper and a graduate student in atmospheric sciences at the University of Washington. “This was unexpected. Some studies assume that primary sulfate is negligible compared to secondary sulfate formed in the atmosphere after emission.”
The research is a component of the 2022 Alaskan Layered Pollution and Chemical Analysis, or ALPACA, project.
The U.S. Environmental Protection Agency has classified Fairbanks as “serious” for persistently violating Clean Air Act standards for PM2.5 levels and has threatened sanctions. For years, the community has tried various methods to improve air quality in the part of Fairbanks North Star Borough that did not meet air quality standards.
The research found that sulfate — primary and secondary — is also the second largest contributor to PM2.5 in Fairbanks, accounting for 15 to 33 percent of the total, the research paper states. It comes just behind wood smoke from space heating.
Although wood smoke from space heating is the largest contributor to PM2.5, this smoke is only a minor supplier of atmospheric sulfate. Burning wood produces sulfur dioxide, the precursor to sulfate created by atmospheric processes, which is equivalent to just 4 percent of the sulfur dioxide produced by burning fuel oil for space heating, according to the newspaper.
Moon and his colleagues analyzed sulfate particles from January 18, 2022 to February 25, 2022, sorting primary and secondary sulfate data into three categories based on particle size. The team collected filter samples in the Fairbanks area and samples over two weeks at the relatively clean Poker Flat Research Range northeast of Fairbanks for comparison.
However, a key question remains unanswered: does a reduction in primary sulfate emissions lead to a reduction in secondary sulfates?
Moon notes in the research paper that switching to ultra-low sulfur heating fuel would likely reduce emissions of primary sulfate and sulfur dioxide, but that more research is needed to understand how the change would affect the formation of secondary sulfate and air quality in general.
Moon added, however, that ultra-low sulfur heating fuel is more expensive and that “it is important to recognize the economic impacts of increasing fuel oil costs, since this financial burden may motivate residents to rely more wood heating and degrade air quality in general. “
The research also confirmed previous work by the Alaska Department of Environmental Conservation that sulfate derived from coal burning was not a major contributor to air pollution in the violation area from Fairbanks. The paper notes that Fairbanks-area power plants burn low-sulfur coal and their smokestacks often emit above the shallow inversion layer.
The ALPACA project aims to better understand how pollution behaves in cold and dark conditions and how atmospheric layers affect pollution events. Nearly 50 scientists from the United States and Europe spent seven weeks in Fairbanks in early 2022 to study the community’s winter air quality.
More information:
Allison Moon et al, Primary sulfate is the dominant source of particulate sulfate during winter in Fairbanks, Alaska, ACS ES&T Air (2023). DOI: 10.1021/acsestair.3c00023
Provided by University of Alaska Fairbanks
Quote: Study finds home heating fuel a direct source of sulfate in Fairbanks’ winter air (February 21, 2024) retrieved February 21, 2024 from
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