Fenceline measurements reveal regional disparities in United States refinery benzene emissions and emission sources

Abstract United States petroleum refineries have measured fenceline ambient concentrations of benzene since 2018 to comply with an Environmental Protection Agency rule. Benzene is a known carcinogen that is present in most fugitive emissions from refineries. Due to sparse air monitoring, most past comparisons of hazardous air pollutant emissions from refineries have relied on facility-reported emissions estimates. The fenceline measurements have the potential to address key questions about observed benzene pollution levels, disparities in performance between refineries, and root causes of emissions that could inform mitigation actions. We analyzed six years of benzene fenceline measurements from 119 US refineries to characterize air pollution trends and disparities and investigate the underlying causes. We found that the refinery net benzene concentrations declined nationally, but state-level differences were persistent, with refineries in Louisiana (mean: 6.5 µ g m −3 ) and Texas (mean: 6.1 µ g m −3 ) exhibiting significantly higher levels compared with California (mean: 1.0 µ g m −3 ) and Washington (mean: 1.2 µ g m −3 ). Notably, differences in facility capacity did not effectively explain differences in measured net benzene levels. We then analyzed measurements at two specific refineries with high net benzene concentrations, identifying likely source areas of benzene leaks. We found that benzene hotspots typically occurred repeatedly at the same sampler locations, implying that persistent emissions sources were not always addressed after initial detection. Our results highlight disparities in the performance of refineries between US states and provide insight into opportunities to reduce fugitive emissions. This work also illustrates the utility of regulatory fenceline measurements, a new and expanding data source, to characterize and mitigate industrial emissions.