St. Louis Region Meets Federal Ozone Standard
The EPA has issued a “Clean Data Determination” for the Missouri part of the St. Louis nonattainment area. The determination confirms that the region's air quality now meets the 2015 8-hour ozone standard. This finding could provide temporary compliance cost relief for manufacturers with operations in the area.
The St. Louis metro area was first designated as a "Marginal" nonattainment area for the 2015 ozone standard in June 2018. This was triggered by air quality monitoring data from 2015-2017 showing ozone levels exceeding the 70 parts per billion (ppb) threshold. The nonattainment zone includes several counties in both Missouri and Illinois. The "Marginal" classification carried specific regulatory implications for manufacturers. While less stringent than higher classifications, it still subjected new major industrial facilities or major modifications to existing ones to stricter New Source Review (NSR) permitting requirements, potentially increasing compliance costs and project timelines. This Clean Data Determination formally acknowledges that air quality monitors across the region showed attainment for the 2023-2025 period. Consequently, the EPA is suspending certain state planning requirements, including the obligation to submit a formal plan demonstrating how the area would meet the standard and associated contingency measures. The relief is not permanent. A Clean Data Determination is distinct from a formal redesignation to "attainment." If future air quality monitoring shows a violation of the ozone standard, the suspension of the planning requirements can be lifted, re-imposing the regulatory obligations on the state and its industries. To achieve a permanent "attainment" status, the state must formally request redesignation from the EPA. This process requires submitting a comprehensive maintenance plan that demonstrates how the St. Louis region will continue to meet the ozone standard for the next 10 years. The improvement in air quality is the result of long-term efforts, including regulations on industrial plants and power plants, advancements in motor vehicle technology, and vehicle inspection programs. Regional initiatives led by groups like the East-West Gateway Council of Governments have also focused on reducing emissions from transportation through better traffic flow and increased use of mass transit.
