Identifying ozone production from oil and gas versus urban emissions sources in the Denver Metro Area and North Front Range of Colorado

Abstract:

During summertime, ozone concentrations in the Denver Metro Area and North Front Range of Colorado often exceed the 8-hour average EPA National Ambient Air Quality Standard (NAAQS) of 75 ppbv. Ambient measurements of ozone, ozone precursors – volatile organic compounds (VOC) and nitrogen oxides (NO_x=NO+NO₂) – and other secondary pollutants such as peroxyacetyl nitrate (PAN) were collected during spring (15 Mar–18 May) and summer (6 Jul–9 Sept) 2015 at the Boulder Atmospheric Observatory (BAO) in Erie, Colorado. These measurements were made in conjunction with airborne measurements from the Shale Oil and Gas Nexus (SONGNEX) field campaign in spring 2015, which focused on studying the air quality impacts of emissions from oil and gas production in the western U.S. Using the in-situ ground-based measurements collected at the BAO field site, we attempt to identify and compare regional ozone production originating from oil and gas emissions (e.g., the Denver-Julesburg oil basin northeast of BAO) with that from urban and mobile sources (e.g., the Denver/Boulder metropolitan area south and west of BAO). We use ozone production efficiency (i.e., the number of molecules of ozone produced per molecule of NO_x oxidized) and emissions ratios of selected VOCs as a metric for comparing ozone production associated with these different sources of emissions as well as seasonal differences between observations collected in spring versus summer.