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Abstract Sulfuryl fluoride (SO₂F₂) is a synthetic pesticide and a potent greenhouse gas that is accumulating in the global atmosphere. Rising emissions are a concern since SO₂F₂has a relatively long atmospheric lifetime and a high global warming potential. The U.S. is thought to contribute substantially to global SO₂F₂emissions, but there is a paucity of information on how emissions of SO₂F₂are distributed across the U.S., and there is currently no inventory of SO₂F₂emissions for the U.S. or individual states. Here we provide an atmospheric measurement-based estimate of U.S. SO₂F₂emissions using high-precision SO₂F₂measurements from the NOAA Global Greenhouse Gas Reference Network (GGGRN) and a geostatistical inverse model. We find that California has the largest SO₂F₂emissions among all U.S. states, with the highest emissions from southern coastal California (Los Angeles, Orange, and San Diego counties). Outside of California, only very small and infrequent SO₂F₂emissions are detected by our analysis of GGGRN data. We find that California emits 60-85% of U.S. SO₂F₂emissions, at a rate of 0.26 ( ± 0.10) Gg yr⁻¹. We estimate that emissions of SO₂F₂from California are equal to 5.5–12% of global SO₂F₂emissions. 

The mean abundance of sulfuryl fluoride (SO2F2) in the global atmosphere has been increasing since at least the 1970s, with ambient air mole fractions exceeding 2.5 parts per trillion (ppt) today. SO2F2 is a synthetic pesticide and a potent greenhouse gas (GHG) used for fumigation - predominantly of wooden structures, and increasingly for agricultural and commodity products as well. Worldwide use of SO2F2 has surged since the use of methyl bromide (CH3Br) for fumigation was largely phased out under the Montreal Protocol. Recent atmospheric measurements and modeling work from the Advanced Global Atmospheric Gases Experiment (AGAGE) indicates that global emissions of SO2F2 have reached a historic high in recent years at roughly 3.0 Gg SO2F2 yr-1. However, under the current UNFCCC emissions reporting guidelines, countries are not required to report their emissions of SO2F2, and thus SO2F2 is not included in most national GHG emissions inventories, leading to a scarcity of information on the global distribution and magnitude of SO2F2 emissions. In the U.S., California is the only state that keeps a public record of statewide SO2F2 use, despite the gas being used for termite fumigation in other warm-climate coastal states such as Florida. To fill this information gap, we use flask-sample measurements of SO2F2 from the NOAA Global Greenhouse Gas Reference Network (GGGRN) and a geostatistical inverse model (GIM) to provide a measurement-based top-down constraint on the magnitude and spatial distribution of SO2F2 emissions across the continental U.S. We find that California emits the vast majority (>90%) of U.S. SO2F2 emissions, with the largest emissions coming from the California South Coast (Los Angeles, Orange, and San Diego Counties), and the second largest from the San Francisco Bay Area. Outside of California, SO2F2 emissions are rarely detected by the NOAA GGGRN. However, despite California's oversized contribution to U.S. SO2F2 emissions, a significantly large fraction (>50%) of the 3.0 Gg yr-1 global emissions budget is still emitted elsewhere. We will present insights gained from the NOAA GGGRN measurements and our inverse modeling work, including a case study on California's SO2F2 emissions and reconciliation with California state SO2F2 usage records.