O3, CH4, CO2, CO, NO2 and NMHC aircraft measurements in the Uinta Basin oil and gas region under low and high ozone conditions in winter 2012 and 2013

Abstract

Instrumented aircraft measuring air composition in the Uinta Basin, Utah, during February 2012 and January-February 2013 documented dramatically different atmospheric ozone (O 3 ) mole fractions. In 2012 O 3 remained near levels of ∼40 ppb in a well-mixed 500-1000 m deep boundary layer while in 2013, O 3 mole fractions >140 ppb were measured in a shallow (∼200 m) boundary layer. In contrast to 2012 when mole fractions of emissions from oil and gas production such as methane (CH 4 ), non-methane hydrocarbons (NMHCs) and combustion products such as carbon dioxide (CO 2 ) were moderately elevated, in winter 2013 very high mole fractions were observed. Snow cover in 2013 helped produce and maintain strong tempera ture inversions that capped a shallow cold pool layer. In 2012, O 3 and CH 4 and associated NMHCs mole fractions were not closely related. In 2013, O 3 mole fractions were correlated with CH 4 and a suite of NMHCs identifying the gas field as the primary source of the O 3 precursor NMHC emissions. In 2013 there was a strong positive correlation between CH 4 and CO 2 suggesting combustion from oil and natural gas processing activities. The presence of O 3 precursor NMHCs through the depth of the boundary layer in 2013 led to O 3 production throughout the layer. In 2013, O 3 mole fractions increased over the course of the week-long episodes indicating O 3 photochemical production was larger than dilution and deposition rates, while CH 4 mole fractions began to level off after 3 days indicative of some air being mixed out of the boundary layer. The plume of a coal-fired power plant located east of the main gas field was not an important contributor to O 3 or O 3 precursors in the boundary layer in 2013.

Quantifying methane emissions in the Uintah Basin during wintertime stagnation episodes

“…Therefore, the visual technique was adopted here, where the ceilometer time series is short enough for manual visual processing to be carried out. Vertical profiles collected using rawinsondes and tethersondes during multiple wintertime cold-air pools in past years within the Uintah Basin, along with numerical model simulations, show that daytime heating results in h generally ranging between 250-500 m in depth in the lower portions of the Basin with a strong gradient in pollutants near the top of the inversion layer (e.g., Neemann et al 2015;Schnell et al 2016;Oltmans et al 2016). Within this mixedlayer, nearly constant potential temperature and pollutant levels are observed.…”

“…The rates of change over multiple days were then used to calculate daily increases in CH 4 at each site. The afternoon periods between 2000 and 2300 UTC were used in the analyses because afternoon mixing redistributes pollutants relatively uniformly with height throughout ~7 5% of the depth of the pollution layer during this time of the day (Oltmans et al 2016;Schnell et al 2016). In contrast, stable to very stable near-surface inversions often exist during the nighttime, morning, and evening, and the observed surface CH 4 mole fractions at these times are not representative of values throughout the boundary layer, with large variations observed with height.…”

Confirmation of Elevated Methane Emissions in Utah's Uintah Basin With Ground‐Based Observations and a High‐Resolution Transport Model

“…Both “bottom‐up” and “top‐down” methods are used to estimate leakage/emission rates of CH 4 and other trace species associated with oil and gas production. Top‐down methods use atmospheric observations, mainly aircraft or ground‐based, and transport models to constrain emissions in source regions (Karion et al, , ; Oltmans et al, ; Petron et al, ). Through a combination of in situ CH 4 concentrations and meteorological transport modeling, emission rates can be inferred (Turner et al, ).…”

Surface ozone in the Colorado northern Front Range and the influence of oil and gas development during FRAPPE/DISCOVER-AQ in summer 2014

“…Several studies have analyzed the O 3 production resulting from oil and gas emissions in the Uintah Basin, Utah (Edwards et al, 2014;Schnell et al, 2016;Oltmans et al, 2016) as well as in the Upper Green River Basin, Wyoming (Schnell et al, 2009;Oltmans et al, 2014;Rappenglück et al, 2014;Field et al, 2015). However, the Colorado Front Range contains more complex land use patterns and population distributions than those areas.…”