Exceptionally Elevated Wintertime Photochemical Ozone Production Associated With Natural Gas Fields

Rapid, cold temperature photochemical ozone production occurs in rural Wyoming and Utah in regions of natural gas production. Sunrise surface ozone concentrations of 10-30 ppb increase to 140-150 ppb soon after solar noon in these events. This photochemical production occurs at temperatures as low as -17°C during in December-March when daily solar energy levels are relatively low. In the winter of 2009-2010, elevated ozone began over ~15,000 km2 of the sparsely populated Uintah Basin when snow pack was established in mid-December and until the day the snow melted in mid-March. During this 3 month wintertime elevated ozone period, there were 521 hours with hourly ozone concentrations above 75 ppb. In the winter of 2011-2012, there was essentially no photochemical ozone production in the Uintah Basin even though oil and gas production was greater than in the winter of 2009-2010. The difference between the two seasons is that the winter of 2011-2012 in the Uintah Basin was devoid of snow cover. It is suggested that the snow cover aids in the formation of strong temperature inversions that trap ozone precursors such as NOx and volatile organic carbons in a shallow layer near the surface. The snow also reflects solar radiation allowing for a doubling of the energy available for the photochemical production of ozone. Finally, it is speculated that the snow may also be acting as a nocturnal reservoir of nitrous acid that is released at sunrise initiating rapid ozone formation. This wintertime ozone formation is putting the respective gas fields into regulatory ozone health exceedences. This in turn is requiring large investments (billion U$ scale) in ozone precursor reduction efforts. It is suggested that similar cold temperature photochemical ozone production is occurring in other regions of natural gas production where winter snow cover and strong temperature inversions are prevalent.