Surface ozone in the Colorado northern Front Range and the influence of oil and gas development during FRAPPE/DISCOVER-AQ in summer 2014

Abstract

High mixing ratios of ozone (O3) in the northern Front Range (NFR) of Colorado are not limited to the urban Denver area but were also observed in rural areas where oil and gas activity is the primary source of O3 precursors. On individual days, oil and gas O3 precursors can contribute in excess of 30 ppb to O3 growth and can lead to exceedances of the EPA O3 National Ambient Air Quality Standard. Data used in this study were gathered from continuous surface O3 monitors for June–August 2013–2015 as well as additional flask measurements and mobile laboratories that were part of the FRAPPE/DISCOVER-AQ field campaign of July–August 2014. Overall observed O3 levels during the summer of 2014 were lower than in 2013, likely due to cooler and damper weather than an average summer. This study determined the median hourly surface O3 mixing ratio in the NFR on summer days with limited photochemical production to be approximately 45–55 ppb. Mobile laboratory and flask data collected on three days provide representative case studies of different O3 formation environments in and around Greeley, Colorado. Observations of several gases (including methane, ethane, CO, nitrous oxide) along with O3 are used to identify sources of O3 precursor emissions. A July 23 survey demonstrated low O3 (45–60 ppb) while August 3 and August 13 surveys recorded O3 levels of 75–80 ppb or more. August 3 exemplifies influence of moderate urban and high oil and gas O3 precursor emissions. August 13 demonstrates high oil and gas emissions, low agricultural emissions, and CO measurements that were well correlated with ethane from oil and gas, suggesting an oil and gas related activity as a NOx and O3 precursor source. Low isoprene levels indicated that they were not a significant contributor to O3 precursors measured during the case studies.

Acyl Peroxy Nitrates Link Oil and Natural Gas Emissions to High Ozone Abundances in the Colorado Front Range During Summer 2015

“…Thus, the idealized BOXMOX simulations support our empirical conclusion that VOCs from oil and natural gas activities contribute to O 3 production on high O 3 days. This is consistent with the findings from several other recent studies on O 3 in the northern Colorado Front Range using a variety of different methods (e.g., Cheadle et al, 2017;Evans & Helmig, 2017;McDuffie et al, 2016;. 4.…”

“…Thus, the idealized BOXMOX simulations support our empirical conclusion that VOCs from oil and natural gas activities contribute to O 3 production on high O 3 days. This is consistent with the findings from several other recent studies on O 3 in the northern Colorado Front Range using a variety of different methods (e.g., Cheadle et al, ; Evans & Helmig, ; McDuffie et al, ; Pfister, Flocke, et al, ). Out of the VOC species that were measured, propane and several larger alkanes such as n‐pentane are the dominant contributors to PPN production in the BOXMOX simulations. In the northern Colorado Front Range, these species predominately come from oil and natural gas sources (e.g., Abeleira et al, ; Gilman et al, ) and thus indicate that high ratios of PPN/PAN observed in the northern Colorado Front Range are driven by the oxidation of emissions from oil and natural gas production.…”

“…Evans and Helmig () partitioned O 3 measurements made over 4 years (2009–2012) at two Front Range locations by wind direction and observed that a majority of elevated O 3 measurements were characterized by transport from areas with large oil and gas emissions. Cheadle et al () used measurements from three individual days in Greeley as case studies to show that a larger abundance of oil‐ and gas‐related species is correlated with higher O 3 mixing ratios. And lastly, regional chemical transport modeling conducted by NCAR as a follow up to the Front Range Air Pollution and Photochemistry Experiment indicates that oil and gas and traffic emissions generally make the largest contributions to local O 3 production during summer 2014 in the NFRMA (Pfister, Flocke, et al, ).…”

“…The northern Colorado Front Range metropolitan area (NFRMA) has been in violation of the EPA National Ambient Air Quality Standard for O 3 since 2008 (CDPHE, 2009). Rapid population growth and increasing oil and natural gas development since the early 2000s have changed the quantity and distribution of emissions of many important O 3 precursors (e.g., Evans & Helmig, 2017;McDuffie et al, 2016).…”

Changes in summertime ozone in Colorado during 2000–2015

“…Other recent research building on campaign observations has provided observational and modeling evidence that O&NG emissions significantly contribute to summer O 3 production within the DJB and NCFR downwind regions (Gilman et al, 2013;Swarthout et al, 2013;McDuffie et al, 2016;Pfister et al, 2017;Cheadle et al, 2017). This association is difficult to prove with the data and tools that were applied here.…”