Impact of Changes in Oil and Gas Production Activities on Air Quality in Northeastern Oklahoma: Ambient Air Studies in 2015-2017.

A total of three ground-based ambient air studies were conducted in February through March of 2015, 2016, and 2017 at the Phillips 66 Research Center in northeastern Oklahoma. C2 -C12 nonmethane hydrocarbons (NMHCs) were measured using whole-air sampling and gas chromatography-mass spectrometry. In 2016 and 2017, online methane and ethane measurements were also conducted. Strong methane-ethane correlation identified oil and gas (O&G) upstream and midstream operations to be the primary methane source. C2 -C5 alkanes were the dominant NMHCs whose average mixing ratio peaked in 2016 before dropping in 2017. This observation is attributed to regional O&G upstream operations, which peaked in 2015. Mean mixing ratios of C2 -C5 alkanes ranged from 0.99 to 16.99 ppb. Measured ratios of i-C5 / n-C5 were 0.97 ± 0.03, 1.18 ± 0.04, and 1.06 ± 0.02 in 2015, 2016, and 2017, respectively, indicating that O&G upstream and midstream operations were their primary source. Photochemical age was estimated using observed ratio between hexane and propane. Emission ratios of NMHCs at zero photochemical age were calculated, which resembled the composition reported in the literature for natural gas field condensate tank flashing. Back-trajectory analysis showed that hydrocarbon-rich plumes came from the south and west directions, where O&G upstream and midstream operations are abundant. High OH reactivity values were calculated from C2 -C6 alkanes mixing ratios, with the average reactivity for the 3 years being 1.55, 1.88, and 1.16 s-1 . This indicates that VOC emissions from O & G operations may contribute to ozone production.