A new study has found that chemical traces from Canada’s 2023 wildfires lingered in the air above Maryland – more than 1,000 miles from where the smoke originated – for months after the visible smoke had disappeared.
The 2023 fire season in Canada sent smoke billowing thousands of miles across the U.S., blanketing East Coast cities and plunging the Washington, D.C., region into air quality alerts.
When the smoke eventually cleared, scientists at the University of Maryland saw an opportunity to examine the chemical fingerprint of the wildfire plumes up close, something much more common in the fire-prone western U.S. than on the East Coast.
Their findings show that wildfire-related compounds remained present in College Park in Maryland months after the smoke had visibly cleared.
Senior author Prof. Akua Asa-Awuku of UMD’s Department of Chemical and Biomolecular Engineering said: ‘Even when the Air Quality Index was good—long after the fires started to dwindle—we still found similar compounds that we saw during the Canadian wildfire event.’
The research team collected air samples from the roof of a UMD building during three June 2023, August 2023 and February 2024. They then used a high-pressure liquid chromatography method to analyse organic acids, carbon-rich compounds known to influence climate and human health.
Although smoke concentrations peaked in June 2023, the August samples taken on a day classified as ‘good’ by the AQI, still contained wildfire-associated chemicals.
Chemistry Ph.D. student Esther Olonimoyo, who led the research, said: ‘We see the persistence of compounds in the atmosphere beyond what the air quality indices tell us. That raises public health concerns that people might still be exposed to certain compounds even after air quality indices have significantly improved.’
The team identified multiple classes of carbonaceous compounds, including some that can be harmful in high concentrations. Asa-Awuku noted that while the AQI reflects levels of five major pollutants, it does not measure the full spectrum of chemical species present in the atmosphere.
It was not until eight months after the wildfires, in February 2024, that researchers observed a substantial decrease in these compounds. Asa-Awuku believes the lingering presence may be the result of atmospheric chemical reactions that transformed the original emissions into longer-lived derivatives.
She explained: ‘They are persistent over time and space, which suggests that they are part of an atmospheric soup that’s generating more and more of these organic compounds with time.’
These findings could inform more accurate wildfire prediction models and help scientists understand how long-range smoke plumes influence ecosystems. Some of the compounds analysed can dissolve in water and be deposited via rainfall, potentially altering soil chemistry and natural biogeochemical cycles.
Olonimoyo plans to continue analyzing the compounds and identify those with unique signatures. ‘Knowing the molecular composition of these plumes is very important in model predictions. The scientific community can make better predictions when they have more accurate knowledge.’
The full research can be read here.
Photo: Anasmeister
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