Measurement of hydrogen sulfide from oil and natural gas production in the Uintah Basin, Utah using PTR-MS

Natural gas production is associated with emissions of a variety of toxic trace gases. While volatile organic compounds (VOCs) have received considerable attention, H2S is also of concern due to the known health impacts of exposure to this hazardous air pollutant. Here, we present quantitative, fast time-response measurements of hydrogen sulfide (H2S) using Proton-Transfer-Reaction Mass-Spectrometry (PTR-MS) instruments. The PTR-MS was operated for measurements of VOCs including H2S at the Horsepool ground site in the Uintah Basin during the Uintah Basin Winter Ozone Study (UBWOS) 2013 campaign. Measurements of H2S from a mobile laboratory in the gas and oil fields were also made by Ultra-Light-Weight PTR-MS (ULW-PTR-MS) during UBWOS 2012. The H2S measurement by PTR-MS is strongly humidity dependent. We compare the humidity dependence determined in the laboratory with in-field calibrations of H2S and determine the H2S mixing ratios for the mobile and ground measurements. The PTR-MS measurements at Horsepool are compared with simultaneous H2S measurements using a Proton-Transfer-Reaction Time-of-Flight (PTR-ToF) and an H2S/CH4 Picarro instrument. The H2S measurements by PTR-MS agree with both instruments within 30% uncertainties. The combination of the two campaigns (UBWOS 2012 & 2013) has shown that on average 1 - 2 ppbv of H2S is present in the Uintah Basin. The correlation between H2S and methane suggests that the source of H2S is associated with the oil and gas extraction in the basin. Significant H2S emissions with mixing ratios of up to 3 ppmv from storage tanks and wells were observed during the mobile lab measurements. This study suggests that H2S emissions associated with oil and gas production can lead to short-term high levels close to point sources, and elevated background levels away from those sources. Our work has also shown that PTR-MS can make reliable measurements of H2S at levels below 1 ppbv.