“…In recent decades, stricter regulations by the U.S. Environmental Protection Agency and state agencies have 20 resulted in lower emissions of black carbon, hydrocarbons (including air toxics), and nitrogen oxides in many urban environments (e.g., Parrish et al, 2002;Peischl et al, 2010;Sather and Cavender 2012;Warneke et al, 2012;Zhou et al, 2014;Kirchstetter et al, 2017) while in other areas, both populated and remote, expansion or emergence of new oil and natural gas (O&G) exploration and production activities has led to higher emissions of air toxics, methane, and non-methane hydrocarbons, e.g., C 2 -C 8 and larger alkanes, benzene and larger aromatic species (e.g., 25 Petron et al, 2012;Gilman et al, 2013;Adgate et al, 2014;Helmig et al, 2014;Pekney et al, 2014;Warneke et al, 2014;Field et al, 2015;Koss et al, 2015;Rutter et al, 2015;Swarthout et al, 2015;Helmig et al, 2016;Prenni et al, 2016;Abeleira et al, 2017;Koss et al, 2017). The impact of higher emissions of such hydrocarbons from oil and gas fields of Utah and Wyoming on wintertime ozone has been assessed through recent measurement and modeling studies (Carter and Seinfeld 2012;Edwards et al, 2014;Rappenglück et al, 2014;Ahmadov et al, 2015).…”