Citation:

Luo, H., M. Astitha, C. Hogrefe, R. Mathur, AND S. Rao. Assessing the manageable portion of the ozone problem in the contiguous United States. JOURNAL OF THE AIR & WASTE MANAGEMENT ASSOCIATION. Air & Waste Management Association, Pittsburgh, PA, 70(11):1136-1147, (2020). https://doi.org/10.1080/10962247.2020.1805375

Impact/Purpose:

By analyzing an annual CMAQ simulation for a hypothetical case with zero anthropogenic emissions, the work in this study attempts to estimate the controllable portion of ambient ozone concentrations. The focus of this study is on quantifying the impact of anthropogenic emissions on the long-term component of the modeled ozone time series since previous work had shown that variations of this component have a strong influence on ozone exceedances. Furthermore, by extracting information about atmospheric variability from a long-term record of ozone observations and combining it with the results from the CMAQ simulation, the study also attempts to estimate the stochastic component of the manageable ozone component. Results of this analysis can potentially help to inform approaches for utilizing model sensitivity simulations in designing effective and efficient measures aimed at meeting and maintaining ambient air quality standards.

Description:

Regional air quality models are widely being used to understand the spatial extent and magnitude of the ozone non-attainment problem and to design emission control strategies needed to comply with the relevant ozone standard through direct emission perturbations. In this study, we examine the manageable portion of ground-level ozone using two simulations of the Community Multiscale Air Quality (CMAQ) model for 2010 and a probabilistic analysis approach involving 29 years of historical ozone observations (1990-2018). The modeling results reveal that the reduction in the peak ozone levels resulting from the total elimination of anthropogenic emissions within the modeling domain is around 13-21 ppb for the 90th -100th percentile range of the daily maximum 8-hr ozone concentrations across the contiguous United States (CONUS). Large reductions in the 4th highest 8-hr ozone are seen in the regions of West (interquartile range (IQR) of 17-33%), South (IQR 22-34%), Central (IQR 19-31%), Southeast (IQR 25-34%) and Northeast (IQR 24-37%). However, sites in the western portion of the domain generally show smaller reductions even when all anthropogenic emissions are removed, possibly due to the strong influence of global background ozone, intercontinental ozone transport, and stratospheric-tropospheric ozone intrusions. Probabilistic estimates of exceedances for several hypothetical thresholds of the 4th highest 8-hr ozone indicate that, in some areas, exceedances of such hypothetical thresholds may occur even under a scenario without anthropogenic emissions given the ever-present atmospheric stochasticity and the current global tropospheric ozone burden.

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