气候变化领域集成服务门户

BACKGROUND: Ambient monitoring data show spatial gradients in ozone (O-3) across urban areas. Nitrogen oxide (NOx) emissions reductions will likely alter these gradients. Epidemiological studies often use exposure surrogates that may not fully account for the impacts of spatially and temporally changing concentrations on population exposure.

OBJECTIVES: We examined the impact of large NOx decreases on spatial and temporal O-3 patterns and the implications on exposure.

METHODS: We used a photochemical model to estimate O-3 response to large NOx reductions. We derived time series of 2006-2008 O-3 concentrations consistent with 50% and 75% NOx emissions reduction scenarios in three urban areas (Atlanta, Philadelphia, and Chicago) at each monitor location and spatially interpolated O-3 to census-tract centroids.

RESULTS: We predicted that low O-3 concentrations would increase and high O-3 concentrations would decrease in response to NOx reductions within an urban area. O-3 increases occurred across larger areas for the seasonal mean metric than for the regulatory metric (annual 4th highest daily 8-hr maximum) and were located only in urban core areas. O-3 always decreased outside the urban core (e.g., at locations of maximum local ozone concentration) for both metrics and decreased within the urban core in some instances. NOx reductions led to more uniform spatial gradients and diurnal and seasonal patterns and caused seasonal peaks in midrange O-3 concentrations to shift from midsummer to earlier in the year.

CONCLUSIONS: These changes have implications for how O-3 exposure may change in response to NOx reductions and are informative for the design of future epidemiology studies and risk assessments.