The ozone climate penalty, NAAQS attainment, and health equity along the Colorado Front Range.

While ozone levels in the USA have decreased since the 1980s, the Denver Metro North Front Range (DMNFR) region remains in nonattainment of the National Ambient Air Quality Standard (NAAQS). To estimate the warm season ozone climate penalty to characterize its impact on Colorado Front Range NAAQS attainment and health equity. May to October ozone concentrations were estimated using spatio-temporal land-use regression models accounting for climate and weather patterns. The ozone climate penalty was defined as the difference between the 2010s concentrations and concentrations predicted using daily 2010s weather adjusted to match the 1950s climate, holding constant other factors affecting ozone formation. The ozone climate penalty was 0.5–1.0 ppb for 8-h max ozone concentrations. The highest penalty was around major urban centers and later in the summer. The penalty was positively associated with census tract-level percentage of Hispanic/Latino residents, children living within 100–200% of the federal poverty level, and residents with asthma, diabetes, fair or poor health status, or lacking health insurance. The penalty increased the DMNFR ozone NAAQS design values, delaying extrapolated future attainment of the 2008 and 2015 ozone standards by approximately 2 years each, to 2025 and 2035, respectively. The ozone climate penalty in parts per billion (ppb) in the Denver Metro North Front Range region, with nonattainment areas located within the gray box. The ozone climate penalty was defined as the difference between ground-level ozone concentrations in the 2010s and concentrations predicted using daily 2010s weather adjusted to match the 1950s climate, holding constant other factors affecting ozone formation.