California emits more of this little-known greenhouse gas than all other US states combined

California, a state known for advancing some of the strictest climate policies in the country, is the nation’s top emitter of a little-known — but very persistent — greenhouse gas, a new study has found.

Sulfuryl fluoride, a common pesticide for treating termites and other wood-infesting insects, lingers in the atmosphere for more than 40 years — where it traps heat and sends it back down to Earth, according to the study, published on Wednesday in Communications Earth & Environment.

And the Golden State is responsible for an enormous share of those sulfuryl fluoride releases, accounting for as much as 12 percent worldwide, per the study. All other U.S. states combined contribute up to 5 percent of those global emissions, the researchers found. 

“Other greenhouse gases like carbon dioxide and methane are found everywhere across the U.S.,” senior author Scot Miller, an assistant professor of environmental health and engineering at Johns Hopkins, said in a statement.

“On our sulfuryl fluoride map, only California lit up like a Christmas tree,” Miller added. 

The researchers analyzed some 15,385 air emissions of sulfuryl fluoride collected between 2015 and 2019 by the National Oceanic and Atmospheric Administration’s (NOAA) Global Monitoring Laboratory.

In addition to working with the Colorado-based NOAA group, the Johns Hopkins scientists also collaborated with a scientist at the University of California, San Diego’s Scripps Institute of Oceanography.

The coast-to-coast research team then traced the sulfuryl fluoride emissions back to their point of origin, while factoring in wind speed and direction, as well as other meteorological variables.

They found that between 60 and 85 percent of sulfuryl fluoride emissions in the U.S. come from California — and predominantly form Los Angeles, Orange and San Diego counties.

“We can now show not only where but also how and why this gas is being emitted,” lead author Dylan Gaeta, a PhD candidate at Johns Hopkins, said in a statement.

The Environmental Protection Agency first approved sulfuryl fluoride for use as a pesticide in 1959. The material gained popularity after many countries started phasing out more reactive fumigants that were depleting the ozone layer, the authors noted.

“It really is a double-edged sword,” Miller said. “Sulfuryl fluoride is less harmful than the banned fumigants, but it also contributes to global warming.”

The researchers were able to attribute the vast majority of California’s sulfuryl fluoride use to a practice called “structural fumigation” — sealing an infested target with an airtight tent, pumping the gas inside to eliminate the pests and then venting it into the atmosphere.

About 85 percent of California’s sulfuryl fluoride emissions stems from structural fumigation, while the remaining 15 percent comes from fumigating agriculture and other commodities, according to the study. 

Looking toward a future in which global nations have pledged to reduce greenhouse gas reductions, the scientists suggested possible solutions to California’s problem.

Because certain basic solutions and bio-based organic solvents can absorb and destroy sulfuryl fluoride, these substances could be situated at the exhaust vents of fumigated structures, the authors noted.

Such a step, they continued, could also reduce exposure risks to area residents and fumigation workers.

“California’s track record shows that it’s been looking at out-of-the-box, creative ways to reduce its greenhouse gas emissions,” Miller said.

“Knowing better what the emissions are and what impact they have will give the state the information it needs to help holistically develop greenhouse gas reduction strategies.”

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