New research has suggested that the nationwide rise of the potent greenhouse gas sulfuryl fluoride comes almost entirely from termite fumigations in the greater Los Angeles area.
Sulfuryl fluoride is a common treatment for drywood termites, bedbugs, cockroaches, and other pests. The Dow Chemical Company developed the gas, also known by its brand name Vikane, in 1959.
Concentrations of sulfuryl fluoride have grown exponentially worldwide: In 1978, it was 0.3 part per trillion. Today it’s more than 2.5 parts per trillion.
The latest research has found that one hot spot in the United States—the greater Los Angeles area—has the highest emissions of sulfuryl fluoride. In the region, sulfuryl fluoride concentrations have topped 400 parts per trillion at times between 2015 and 2017, said graduate student Dylan Gaeta of Johns Hopkins University. The second-highest emissions came from California’s Bay Area. The rest of the country releases barely any emissions.
According to the state’s Department of Pesticide Regulation, the source of emissions in California is clear: Structural fumigations account for 99% of sulfuryl fluoride use.
The study analyzed the concentration of sulfuryl fluoride in the air between 2015 and 2017 taken by NOAA’s Global Monitoring Laboratory. The agency’s scientists regularly gather flasks of air across the country using aircraft, towers, and surface collectors. NOAA scientists in Boulder, Colo., then test the flasks for minute traces of gas.
Gaeta and his collaborators used these measurements to estimate the rate of emissions nationwide. They fed a statistical model sulfuryl fluoride concentration measurements at different sites, along with other relevant data, and asked the model to infer where the emissions came from.
“We expected to see little splotches of emissions throughout at least some other parts of the country,” Gaeta said. “The fact that we are seeing almost all of it from California? That was the shocking part.”
NOAA’s monitoring network does not extend to Florida, however, and the state does not track sulfuryl fluoride use. “It is possible that Florida is also emitting, and then it’s just not being detected by the NOAA network,” said Gaeta. He presented the research, which has not yet been peer reviewed, at AGU’s Fall Meeting 2021.
A Surprise Greenhouse Gas
For years, the insecticide was thought to be relatively harmless when it came to global warming.
To use the substance, fumigators first cover a building with an airtight tent. They fill the building with gas and let it do its work. Afterward, workers open windows to air out the building, releasing the gas to the atmosphere, where it was believed to break down relatively quickly.
The method rose in popularity after the Montreal Protocol phased out another common fumigant, methyl bromide, that was found to erode the ozone layer.
But research in 2008 and 2009 revealed that sulfuryl fluoride has a relatively high global warming potential and sticks around longer than initially thought. The gas has a global warming potential of more than 4,000 times that of carbon dioxide over 100 years and remains in the atmosphere for about 36 years.
“When something stays in the atmosphere this long, you cannot lessen the climate effects overnight by just turning off the emissions,” said atmospheric chemist Mads Sulbaek Andersen of California State University Northridge, who has studied the gas’s characteristics but was not involved in the new research.
The California Air Resources Board (CARB) recently added the insecticide to its list of short-lived climate pollutants. It’s the only state to track its use, with records stretching back to the 1990s. Yet the state’s progressive emissions goals don’t include sulfuryl fluoride because the rules were written before scientists knew it was a greenhouse gas.
“CARB staff continue to monitor the scientific literature to better understand the greenhouse gas emissions and effects of sulfuryl fluoride and other pesticides,” said CARB public information officer Dave Clegern.
You can rid your house of pests without fumigation, but other methods may not work as well, said urban pest researcher Andrew Sutherland at University of California Agriculture and Natural Resources (UC ANR). Other techniques to target drywood termites, bedbugs, and wood-boring beetles include heat treatments and local insecticide application. Both require advanced monitoring, detection, and delimitation methods, said Sutherland.
But when infestations are widespread, nothing can equal sulfuryl fluoride’s “efficacy and cost-effectiveness,” Sutherland said.
Los Angeles County integrated pest management adviser Siavash Taravati of UC ANR said that sulfuryl fluoride comes in handy when an infestation is inaccessible to technicians. “If banned, pest control operators will have to switch to local treatment methods.”
The change could reverberate around the world: According to recent work from the Massachusetts Institute of Technology, structural fumigation in North America was the leading global source of sulfuryl fluoride emissions in 2019.
If California fumigations stopped, said Gaeta, “almost all the emissions coming from the U.S. would go away.”
—Jenessa Duncombe (@jrdscience), Staff Writer