California Leads the Nation in Emissions of a Climate Super-Pollutant, Study Finds

California emits more sulfuryl fluoride, a potent greenhouse gas and toxic pesticide, than the rest of the lower 48 states combined, a new study concludes. 

The study, published Wednesday in the journal Communications Earth & Environment, comes after California—a state that touts its leadership role in addressing climate change—denied a recent request to include the emissions in its annual greenhouse gas inventory and phase out the pollutant.

“This is a greenhouse gas that is not being treated as a greenhouse gas and has sort of slipped under the radar,” said Dylan Gaeta, an environmental health and engineering researcher at Johns Hopkins University and the study’s lead author. 

Sulfuryl fluoride is a synthetic pesticide used primarily as a fumigant for homes and other buildings infested with “drywood” termites, which nest aboveground in the structures’ wooden beams.  

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The gas is also used to fumigate dried fruits, nuts and other agricultural products to keep them insect-free during storage. As a greenhouse gas, sulfuryl fluoride is 7,510 times more potent at warming the climate than carbon dioxide on a pound-for-pound basis in the first 20 years after being released into the atmosphere.

Drywood termites are most prevalent in hot, dry regions. Three counties in southern California—Los Angeles, Orange and San Diego—make up the majority of the fumigant’s use in the state. Structures treated with sulfuryl fluoride are covered in large tents for several days while the gas is released inside. Once the fumigation is complete, the gas is vented into the atmosphere.

Approximately 260 metric tons of sulfuryl fluoride is released into the air in California each year, according to the study, which analyzed air samples collected from an air monitoring network that spanned the lower 48 states from 2015 to 2019. Emissions from California represent 60 percent to 85 percent of all sulfuryl fluoride released in the contiguous United States. Releases of the gas from California alone are equal to the annual greenhouse gas emissions of approximately 465,000 automobiles.

Actual emissions may be even higher. California’s Department of Pesticide Regulation reported that 1,367 metric tons of sulfuryl fluoride was used in 2019, a figure more than five times higher than the 260 metric tons of emissions from California detected in the current study.   

Gaeta said it’s possible that state data may over-report actual sulfuryl fluoride use or that the air monitoring network used in the study may have missed some of the emissions.  

In addition to being a potent climate pollutant, sulfuryl fluoride is highly toxic. The gas targets the nervous system and can cause severe irritation of the nose, eyes, throat and respiratory system, leading to multiple serious problems, including shortness of breath, weakness, nausea, numbness, stomach pain, vomiting, muscle twitching, seizures and death. 

Long-term effects of exposure include cancer, cognitive problems and reproductive damage. Because it’s an odorless, colorless gas and doesn’t irritate the eyes or skin at normal concentrations, exterminators are required to use trace amounts of another fumigant (chloropicrin) that has a strong odor and irritates the eyes and respiratory tract as a warning agent.

More than 80 sulfuryl fluoride poisoning complaints were registered with the California Department of Pesticide Regulation between 2015 and 2019, causing poisoning victims to lose a total of more than 3 weeks of work.

In 2016, a man broke into an apartment in Alameda County about 18 hours into a sulfuryl fluoride fumigation. He started sweating profusely, had trouble breathing and asked a security guard to get him medical care. The burglar died on the way to the hospital. The exterminator had not used chloropicrin and was cited for violating state law.

“It’s a double whammy, worsening our climate crisis and then killing people who are also exposed to the gas,” Jonathan Evans, environmental health legal director for the Center for Biological Diversity, an environmental organization based in Tucson, said of sulfuryl fluoride.

The study follows a report last month by Beacon Economics, an independent research firm, and Next 10, an environmental nonprofit, finding California is not on track to meet its emissions reduction targets.

State law requires California to reduce greenhouse gas emissions by 40 percent below 1990 levels by 2030. The California Air Resources Board (CARB) set a more aggressive goal in 2022 to reduce greenhouse gas emissions by 48 percent below 1990 levels by 2030.

“On the one hand, the Air Resources Board is saying we need to do more to address climate change, and on the other hand, they’re failing to really take steps in the context of sulfuryl fluoride to reduce this highly potent greenhouse gas,” Evans said.

The Center for Biological Diversity filed a formal petition in 2022 asking the Air Resources Board to add sulfuryl fluoride to the agency’s annual greenhouse gas emissions inventory and phase out the use of sulfuryl fluoride in the state.

The Air Resources Board declined both requests, stating in February 2023 that “CARB is committed to further dialogue and further study of this issue.”

“The response we got from the Air Resources Board was very disheartening,” Evans said. “We have an obligation to really reduce these emissions if we want to reduce our overall greenhouse gas emissions and continue being a leader in the fight against climate change.”

“CARB is tracking information and research about sulfuryl fluoride and collaborating with the California Department of Pesticide Regulation,” said Lys Mendez, a spokesperson for the Air Resources Board. “As part of its commitment to address greenhouse gas emissions and their impact on human health, CARB will track information as it becomes available before it can determine any future action on sulfuryl fluoride, including availability of pest control alternatives.”

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In its response to the Center for Biological Diversity’s petition, the agency stated that it “is a global leader in developing and implementing actions to mitigate climate change” and “partners around the world look to California as a model for decarbonization across all economic sectors.”

However, the Air Resources Board noted that “to date, research indicates that alternatives are not sufficiently viable to replace sulfuryl fluoride for its necessary uses for residential termite fumigation and agricultural commodity fumigation.”

One alternative for treating homes and other structures would be to capture the sulfuryl fluoride inside the building after fumigation is complete rather than vent the gas into the atmosphere. The current study noted that chemical solvents can be used to absorb and destroy sulfuryl fluoride, but that additional work would be required to reduce cost and technical barriers.

In the meantime, the state should begin counting sulfuryl fluoride in its annual greenhouse gas emissions inventory, Gaeta, of Johns Hopkins, said.

“California has these goals on the books of getting to net zero greenhouse gas emissions by the year 2045,” he said. “But in order to get to net zero emissions the state, and the U.S., needs an inventory of all of the greenhouse gases that are being emitted.”

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