EPA Splits Ozone Nonattainment Areas and Reduces Regulatory Burdens Across Parts of Maryland, Delaware

PHILADELPHIA - Today, U.S. Environmental Protection Agency (EPA) approved Maryland and Delaware's requests to redesignate Cecil County, Maryland, and New Castle County, Delaware, as separate ozone nonattainment areas (NAA) from the Philadelphia ozone NAA. This action, based on gold standard scientific data, recognizes that improved air quality in both Cecil and New Castle counties and will lift regulatory burdens on local businesses while ensuring progress towards cleaner air counties. Through this final rule, the Trump EPA is proving, once again, that protecting human health and the environment while growing the economy is not a binary choice.

"Today's action reflects a careful, science-based review demonstrating Cecil County and New Castle County are not driving ozone problems in the Philadelphia area," said EPA Mid-Atlantic Regional Administrator Amy Van Blarcom-Lackey. "This boundary update recognizes local air quality progress while keeping in place the Clean Air Act protections that safeguard human health and the environment."

After conducting a standard five-factor analysis and careful review, EPA has determined that activity in these counties do not lead to any air quality violations in the Philadelphia ozone NAA. This means these counties can be separated from the Philadelphia ozone NAA without compromising on improving the region's air quality.

Additionally, based on two three-year periods of quality-assured and certified data, EPA is issuing clean data determinations (CDD) for both counties for the 2008 and 2015 ozone National Ambient Air Quality Standards (NAAQS). The CDDs would suspend the obligations of Maryland and Delaware to submit certain nonattainment planning requirements for their respective NAAs for as long as the areas continue to attain the 2008 and 2015 ozone standards.

EPA, through cooperative federalism, will continue to work with Maryland and Delaware to promote prosperity in the states while fulfilling the agency's core mission of protecting human health and the environment.

To read the final rule please visit https://www.federalregister.gov/d/2026-11169Exit EPA's website.

Background

On February 13, 2025, Maryland's governor and on August 15, 2025, Delaware's governor requested EPA revise the designation for the Philadelphia-Wilmington-Atlantic City area for the 2008 and 2015 primary and secondary ozone NAAQS.

An NAA is a region where air quality does not meet EPA's NAAQSExit EPA's website for certain pollutants, as defined by the Clean Air Act. These classifications help provide information on air quality within a given area. NAAs can be made up of multiple counties, parts of different states, or even large metropolitan regions that cross state lines.