Decadal Trends and Variability in Intermountain West Surface Ozone near Oil and Gas Extraction Fields

Air Methods & Monitoring
Oral Presentation

Prepared by B. Sive1, Y. Zhou2, H. Mao2
1 - National Park Service, Air Resources Division, 7333 W. Jefferson Ave, Lakewood, CO, 80235, United States
2 - State University of New York College of Environmental Science and Forestry, Department of Chemistry, Syracuse, NY, 13210, United States

Contact Information:; 303 987 6947


Decadal trends in the annual fourth-highest daily maximum 8-hour average (A4DM8HA) ozone (O3) were studied over 2005 – 2015 at 13 rural/remote sites in the U.S. Intermountain West to investigate the impact of oil and natural gas (O&NG) emissions on decadal O3 levels. No trends were observed in A4DM8HA O3 at two reference sites, which are located upwind of and thus minimally influenced by emissions from O&NG production regions. Trends, or a lack thereof, varied widely at 11 sites in/near O&NG basins resulting from different controlling factors rather than a simplistic, uniform one. A lack of trend was observed at 8 sites, including Rocky Mountain National Park (ROMO), and was likely caused by the increasing O&NG emissions and decreasing emissions from other activities. ROMO is located to the west of the Denver-Julesburg Basin and experienced northwesterly and southeasterly wind most frequently over 2005 – 2015, with higher O3 (>60 ppbv) from the east and southeast. Natural gas production in Weld County increased by nearly a factor of 3 from 2009 to 2015, which coincided with use of horizontal drilling starting in 2009. Additionally, NOx emission reductions of ~37% from the urban area of Denver offset the effect of increased NOx emissions from O&NG extraction. The decadal (2005 – 2015) mean of the A4DM8HA O3 reached or exceeded 70 ppbv, the current National Ambient Air Quality Standard, at three sites in the Intermountain West, including ROMO (75.1 ppbv). Decreasing trends were observed at three sites and were attributed to decreases in natural gas production, emission reductions in coal-fired electricity generation, and increasingly frequent precipitation weather. Our findings suggest that emissions from O&NG extraction played a significant role in shaping long-term trends in surface O3 near/within O&NG regions and warrants consideration in the design of efficient O3 mitigation strategies for the Intermountain West.