Toronto's COVID Pause Reversed This 'Forever Chemical

Scientists watching Toronto's air quality got the shock of their careers when lockdowns began in 2020. A stubborn forever chemical that seemed impossible to control suddenly started disappearing.

The pollutant is trifluoroacetic acid, or TFA, the smallest member of the PFAS family of forever chemicals. When people stopped their normal routines during COVID lockdowns, TFA levels in Toronto's atmosphere dropped fast and significantly.

"When we turned off the tap, so to speak, we saw a really quick response," says Professor Cora Young, an atmospheric chemist at York University who led the study. She was so surprised by the data that she checked it two more times before believing it.

The team collected monthly air samples from 2018 to 2024 on the roof of York University's science building. They measured both rain and snow samples, plus the invisible gases and particles that settle on surfaces like dust on a windshield.

The discovery changes everything scientists thought they knew about TFA. Researchers previously believed it came from long-lived chemicals that hang around for years. Instead, the rapid drop during lockdowns proved TFA forms quickly from short-lived emissions, likely from sources like car air conditioners and industrial facilities.

That's actually wonderful news. If TFA responds immediately when we reduce certain emissions, we can figure out how to minimize it. "We could have a lot more control over this than we previously thought," Young explains.

The catch? As Toronto returned to normal life, TFA levels crept back up. They peak in summer when sunlight helps create the chemical from various emissions mixing in the air.

The Bright Side

This accidental experiment during lockdowns handed scientists a roadmap for tackling forever chemicals. For the first time, researchers can pinpoint TFA's thousands of sources instead of watching helplessly as it accumulates everywhere from Arctic ice to Antarctic snow.

The timing matters because TFA is already showing up in unexpected places. Scientists are finding it concentrated in plants and food, even in human blood. While researchers don't yet know the health effects of long-term exposure, TFA levels in the environment already dwarf other PFAS chemicals that triggered massive lawsuits and hundred-million-dollar payouts.

Modern car air conditioners switched to chemicals that create TFA specifically to help the climate, replacing older refrigerants that damaged the ozone layer and acted as potent greenhouse gases. Every car sold in North America since 2019 uses these newer compounds.

Now scientists know these replacement chemicals aren't as benign as hoped, but they also know something more important: we can measure the problem, trace its sources, and potentially fix it. "If we don't know where it's coming from, it's very difficult for us to regulate," Young notes.

The pandemic revealed an unexpected silver lining in Toronto's air.