Efficacy of recent state implementation plans for 8-hour ozone

Abstract

The development of state implementation plans (SIPs) for attainment of criteria pollutant standards is an integral component of air quality management in the United States. However, the content and efficacy of SIPs have rarely been examined systematically. Here, 20 SIPs developed in response to the 1997 8-hr ozone standard are reviewed as case studies of attainment efforts at the state level.Comparison of observed and model predicted ozone concentrations shows the U.S. Environmental Protection Agency (EPA) recommended modeled attainment test to be a somewhat conservative predictor of attainment. Among 12 SIPs for regions that sought attainment by 2009, the test correctly predicted attainment and nonattainment in four and five regions, respectively; in the other three regions, attainment was observed despite predictions of nonattainment. However, weight-of-evidence determinations and deviations from the recommended modeled attainment test methodology led five of these SIPs to predict attainment that was not in fact observed by 2009; three of those regions achieved attainment in 2010. Ozone and NO 2 concentrations declined across much of the United States during the period covered by the SIPs, with rates of improvement strongly correlated with the initial pollution levels and hence greatest in nonattainment regions. However, at monitors with mid-range levels of ozone initially, rates of reduction were largely independent of the initial attainment status of the region. This is consistent with the fact that apart from California, the majority of ozone precursor reductions documented by SIPs resulted from federal measures rather than from state or local controls specific to the nonattainment regions.Implications: At a time of sharp debate in the United States about strengthening ambient ozone standards, this study highlights strengths and weaknesses of recent state implementation plans. Substantial improvements in air quality have been observed, bringing the majority of regions into attainment of the 1997 ozone standards. The extent to which state-level measures contributed to those improvements is unclear. The standard modeled attainment tests provided somewhat conservative predictions of future attainment, but alternate approaches predicted attainment that was not in fact observed. Greater caution may be needed in weight-of-evidence analyses to avoid overly optimistic predictions of future attainment.

Modeled and observed fine particulate matter reductions from state attainment demonstrations

“…Some of the larger improvement in nonattainment regions than in attainment regions reflects a general trend of greater improvements at monitors that were more polluted in earlier years. The correlation between initial air quality and the magnitude of improvements parallels the findings of Pegues et al (2012), who showed that ozone and nitrogen dioxide (NO 2 ) reductions were greatest in regions where pollution levels were initially highest. The effect of nonattainment status can be isolated by considering monitors with similar initial DVs.…”

“…The weight-of-evidence determinations proved to be a helpful supplement to the attainment test in the attainment demonstrations considered here, as they allowed states to document localized controls and other considerations that counteracted false-alarm predictions of nonattainment. Caution is still needed in reviewing weight-of-evidence determinations, since for both ozone and PM 2.5 they have almost uniformly been used to suggest pollution levels will be lower than modeled; as documented by Pegues et al (2012), this led to false predictions of attainment in some ozone attainment demonstrations. Nevertheless, the cases considered here paint an overall picture of success in achieving the previous PM 2.5 standard, and substantial progress toward achieving the new one.…”

“…These attainment demonstrations represent the first opportunity to evaluate the performance of the speciated PM 2.5 test in regulatory practice, since the test was set forth in an EPA guidance document in 2007. The modeled attainment test for PM 2.5 faces greater challenges than the similar one for ozone evaluated by Pegues et al (2012), since it must consider PM on a speciated basis in predicting future concentrations. As noted earlier, the test for PM faces the added complication that speciation is not directly measured at most monitors and must be inferred from nearby speciation monitors.…”

“…Pegues et al (2012) evaluated the performance of SIPs in achieving attainment of the 1997 ozone standard, and compared rates of air quality improvement in regions that were and were not required to develop an attainment demonstration. However, the methodology of the speciated modeled attainment test for PM 2.5 and its performance in predictions of pollutant levels have not been evaluated previously in the peer-reviewed literature.…”

Evaluating the effectiveness of air quality regulations: A review of accountability studies and frameworks

“…A few studies use population-weighted concentration (Hou et al, 2010) and personal exposure monitoring (Wu et al, 2010). Some studies opt to not assess exposure and instead apply statistical techniques that test for a change in health outcomes rates over the predefined time period of the intervention (Greenstone, 2004;Pegues et al, 2012;. Specific issues in relating air quality changes to exposures when conducting accountability studies include diagnosing both model uncertainty and parameter uncertainty in model selection (Morgenstern et al, 2012), missing data (Bell et al, 2011;Van Erp et al, 2011), and estimating baseline exposure for the no-control case that accounts for appropriate confounders (Health Effects Institute, 2003).…”