Spatial and Temporal Variability in Atmospheric Emissions from Oil and Gas Sector Sources in the Marcellus Production Region

Temporal variability in emissions from oil and gas supply chains depends on the spatial scale at which emissions are aggregated. Emissions of methane, ethane, volatile organic compounds (VOCs) and nitrogen oxides (NOx) from oil and gas facilities in the Marcellus production region were estimated at a one-hour time resolution for calendar year 2023. Emissions from more than 200,000 well sites were included in the analyses and hourly emissions were aggregated at the grid cell (4 km by 4 km), county and basin level. Ratios of maximum to annual average hourly predicted emission rates were calculated at the grid cell, county and basin level for each pollutant. Maximum to average emission rate ratios decreased as the scale of spatial aggregation increased. At the grid cell level, ratios of maximum to average emission rates exceeded 100 in some grid cells for hydrocarbon emissions such as VOCs. In contrast, basin level maximum to average ratios for NOx emission rates were less than 1.1. The sources driving temporal variability for hydrocarbon emissions were well completions and liquid unloadings, while the sources driving temporal variability in NOx emissions were pre-production activities such as drilling and hydraulic fracturing. Accurately reconciling predicted emissions with measurements requires accounting for the timing, duration, and frequency of intermittent events, and depends on the type of measurements being made.