Spatial patterns in summertime surface ozone in the Southern Front Range of the U.S. Rocky Mountains

Abstract

Summertime ozone in the Western United States presents a unique public health challenge. Changes in population, background ozone, wildland fire, and local precursor emissions combined with terrain-induced meteorology can affect surface ozone levels and compliance with the National Ambient Air Quality Standards (NAAQS). While there is considerable research on ozone in the Northern Front Range Metropolitan Area of Colorado, United States, less is known about the Southern Front Range. In Colorado Springs, approximately 100 km south of Denver, summertime maximum daily 8-h average (MDA8) ozone shows no significant (p < .05) trend at the 5th, 50th, or 95th percentile over the past 20 years. However, the region is at risk of nonattainment with the NAAQS based on observations from 2018 to 2020. From June through September 2018, the Colorado Department of Public Health and Environment measured hourly ozone at eight sites to characterize the spatial distribution of ozone in Colorado Springs. Mean ozone (±1σ) ranged from 34 ± 19 to 60 ± 9 ppb. The 95th percentile of hourly ozone increased approximately 1.1 ppb per 100 m of elevation, while the amplitudes of mean diurnal profiles decreased with elevation and distance from the interstate. MDA8 ozone was also highly correlated across all sites, and there is little evidence of local photochemical production or ozone transport from Denver. Further, results from generalized additive modeling show that summertime MDA8 in this region is strongly influenced by regional background air and wildfire, with smoke contributing an average of 4–5 ppb to the MDA8. Enhanced MDA8 values due to wildfires were especially pronounced in 2018 and 2020. Lastly, we find that the permanent monitoring sites represent the lower end of observed ozone in the region, suggesting that additional long-term monitoring for public health may be warranted in populated, higher elevation areas.

Synthesis of Satellite and Surface Measurements, Model Results, and FRAPPÉ Study Findings to Assess the Impacts of Oil and Gas Emissions Reductions on Maximum Ozone in the Denver Metro and Northern Front Range Region in Colorado

“…These were used to track trends and relationships with other variables from 2010 to 2019. Data for the year 2020 was not used because of frequent wildfire smoke (Albores et al., 2023; Flynn et al., 2021). Data were acquired for the FTCW, WCT, RFLAT, NREL, and CHAT sites.…”

Maximum ozone concentrations in the southwestern US and Texas: Implications of growing predominance of background contribution

“…Similarly, Abeleira and Farmer (2017) found that ozone in the Denver urban area was either stagnant or increasing between 2000 and 2015, despite substantial reductions in NOX emissions. In Colorado Springs, approximately 100 km south of Denver, Flynn et al (2021) found that summertime MDA8 ozone shows no significant trend throughout its distribution over the past 20 years. Further, they found little evidence of local photochemical production or ozone transport from Denver, consistent with our classification of this area as rural.…”

Synthesis of Satellite and Surface Measurements, Model Results, and FRAPPÉ Study Findings to Assess the Impacts of Oil and Gas Emissions Reductions on Maximum Ozone in the Denver Metro and Northern Front Range Region in Colorado

“…These were used to track trends and relationships with other variables from 2010-2019. Data for the year 2020 was not used because of frequent wildfire smoke (Albores et al, 2023;Flynn et al, 2021) To test for the effects of meteorology on trends in O3, June-August mean 500 hPa heights were acquired from the National Center for Environmental Prediction (NCEP) Reanalysis for a 2.5° by 2.5° grid cell centered on 40°N 105°W which contains the DM/NFR. The NCEP Reanalysis meteorological data product is described by Kalnay et al (1996).…”