EPA Redraws Ozone Map, Splits Counties Three Ways
Published Date: 6/4/2026
Rule
Summary
The EPA is updating air quality rules for Cecil County, MD, and New Castle County, DE by splitting a big pollution area into three smaller ones, making it easier to manage ozone pollution. Both states asked for this change, and the EPA agrees they’ve cleaned up enough to meet 2008 and 2015 ozone standards. These changes take effect July 6, 2026, helping communities breathe easier without extra costs.
Analyzed Economic Effects
2 provisions identified: 1 benefits, 1 costs, 0 mixed.
Clean Data Determinations Suspend SIP Plans
The EPA issued clean data determinations (CDDs) for the Cecil County, MD and New Castle County, DE nonattainment areas based on 2022-2024 ambient monitoring data. Because Cecil County's most recent three-year design value is 67 ppb and New Castle County's is 68 ppb, the EPA is suspending each State's obligation to submit attainment demonstrations, reasonably available control measures (RACM), reasonable further progress (RFP) plans, contingency measures, and other attainment-related planning SIPs for the 2008 and 2015 ozone standards for as long as the area continues to meet the standards; the rule is effective July 6, 2026.
Nonattainment Area Split Keeps OTR Rules Intact
The EPA split the former Philadelphia-Wilmington-Atlantic City, PA-NJ-MD-DE nonattainment area into three separate nonattainment areas (Cecil County, MD; New Castle County, DE; and Philadelphia-Atlantic City, PA-NJ) while keeping all areas designated nonattainment (Marginal for the 2008 ozone NAAQS and Serious for the 2015 ozone NAAQS). The rule does not remove these areas from the Ozone Transport Region (OTR) requirements in 40 CFR 51.1116 and 51.1316, so OTR obligations continue to apply.
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Key Dates
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