The impact of detailed spatial and temporal allocation of unconventional oil and gas development (UOGD) NOx emissions on predicted ozone formation was examined using hydraulic fracturing emissions in the Eagle Ford Shale region of Texas as a case study. Hydraulic fracturing occurs at specific well sites, lasting only 1-2 weeks prior to production. Four scenarios for spatial and temporal allocation of hydraulic fracturing NOx emissions were developed. In one scenario, NOx emissions were evenly distributed to all active wells in the Eagle Ford region, with continuous emissions throughout the year. In other scenarios, NOx emissions from hydraulic fracturing engines in Karnes County were allocated only to fractured wells, with durations ranging from 2 days to 2 weeks. In the month of August, predicted daily maximum of 8 h average (MDA8) O