Effects of Oil and Gas Well Site Proximity on Ambient Air Pollutant Concentrations in California

Abstract:

An estimated 17.6 million people in the United States live within 1.6 km of an active oil or gas well, including 2.1 million California residents. California has the fifth-largest share of U.S. crude oil reserves and is the seventh-largest producer of crude oil in the nation, accounting for about 4% of total U.S. production in 2018. However, the effects of oil and gas preproduction and production activities on air quality are not well characterized. We obtained oil and gas production data from Enverus and the California Geologic Energy Management Division (CalGEM), and air pollutant concentration data from the US EPA Air Quality System for 284 monitors throughout California, with daily concentrations of CO, NO2, O3, SO2, and particulate matter with a diameter of less than 10 µm (PM10) and less than 2.5 µm (PM2.5). For each air monitor daily observation during the study period (1999-2019), we assessed exposure to upwind wells in the preproduction and production stages. For each pollutant, we fit crude linear regression models and adjusted fixed effects models that account for meteorologic, geographic, and temporal factors, such as wind direction, daily total precipitation, daily mean air temperature, monitor location, month, and year. We found evidence that exposure to well sites is associated with higher concentrations of ambient air pollutants, which may contribute to adverse health outcomes. Our results support the use of proximity-based methods to assess exposure to oil and gas wells in population health studies and suggest such wells could be an important source of local air pollution.