Fig. 1

Number of UOG air sampling studies by geologic formation. Air sampling has been performed in various UOG sites in the US. The most commonly sampled site in studies identified by our search was the Barnett Shale located in TX. The least frequently studied were Eagle Ford Shale, Fayetteville Shale, Haynesville Shale, and Powder River Basin. TX, Texas; AR, Arkansas; OK, Oklahoma; LA, Louisiana; MT, Montana; WY, Wyoming; NY, New York; MD, Maryland; PA, Pennsylvania; WV, West Virginia; OH, Ohio; VA, Virginia; KY, Kentucky; TN, Tennessee; CO, Colorado; ND, North Dakota; UT, Utah; KS, Kansas; NE, Nebraska; UOG, unconventional oil and gas