Seminar

Abstract

In the United States, Colorado and Utah rank 5^th and 9^th, respectively, in the production of natural gas, and 10^th and 11^th, respectively, for domestic crude oil production. Raw natural gas surfacing at a completed wellhead is a mixture of approximately 75 mole percent methane (C1) while the remaining fraction is mostly composed of ethane (C2), propane (C3), and higher hydrocarbons (C4-C6+) that are subsequently distilled. An extensive set of volatile organic compounds (VOCs) and other trace gases were measured in the ambient air near two highly active areas of oil and natural gas production in Colorado's Denver-Julesburg Basin and Utah's Uintah Basin. The Colorado study took place in February-March 2011 at the NOAA Boulder Atmospheric Observatory (BAO) in southwestern Weld County as part of the Nitrogen, Aerosol Composition, and Halogens on a Tall Tower (NACHTT) experiment. The Utah study took place in January-February 2012 in northeastern Utah as part of the Uintah Basin Winter Ozone Study (UBWOS). Both of these data sets are characterized by 1) highly elevated hydrocarbon mixing ratios and 2) very strong correlations amongst the alkanes and several aromatics indicating a common source for all of these compounds. For example, the median mixing ratios for propane were 16 and 31 ppbv during the Colorado and Utah studies, respectively, which is substantially greater than median urban values that range between 1-5 ppbv. The VOC measurements from these two studies will be compared to previous experiments in Pasadena, CA and other sites in Colorado's northern Front Range to show that the chemical signature associated with oil and natural gas operations is very distinctive and can be clearly differentiated from urban VOC emission sources that are dominated by vehicular exhaust. We will compare the regional characteristics of the Colorado and Utah data sets in order to assess the potential atmospheric impacts of VOC emissions from the oil and gas sector, such as the photochemical production of ozone.