Regional Impacts of Unconventional Oil and Gas Operations on Ozone and Air Toxics

Abstract Unconventional oil and gas development (UOGD) has expanded over the past three decades and now accounts for most of U.S. oil and natural gas production. Although prior studies link local UOGD activity to health outcomes, they provide limited evidence directly attributing ambient pollutant levels to UOGD emissions. We address this gap by quantifying UOGD impacts on ozone and air toxics using the Community Multiscale Air Quality (CMAQ) model with the Integrated Source Apportionment Method (ISAM), enabling an explicit linkage between UOGD emissions and ambient concentrations. UOGD activities produce substantial local contributions to primary air toxics and continental-scale influences on ozone. Across CONUS, UOGD increases population-weighted annual averages of maximum daily average 8-h (MDA8) ozone, 1-h benzene, 1-h nitrogen dioxide (NO2), and 1-h formaldehyde (HCHO) concentrations by roughly 1 ppb, 1.1 ppt, 0.035 ppb, and 0.03 ppb, respectively. Annual maximum UOGD contributions to MDA8 ozone are about half of those from other anthropogenic sources. ISAM also reveals unexpectedly large UOGD-driven ozone enhancement (up to 4–5 ppb) in the Los Angeles region from Texas emissions, a feature less evident in brute-force sensitivity tests. These findings highlight the need to further examine interstate UOGD influences on nonattainment areas and source-impact quantification methods.