2025 ozone data shows continued progress in regional air quality

The metropolitan Washington region experienced five "Code Orange" unhealthy air days in 2025, a decrease from seven days in 2024, according to data collected as part of the Metropolitan Washington Council of Governments' Ozone Season Summary. The data was presented on September 24 by COG staff to the Metropolitan Washington Air Quality Committee (MWAQC).

In 2025, the region had the third lowest number of days exceeding the U.S. Environmental Protection Agency's National Ambient Air Quality Standards (NAAQS). For comparison, in 2015, there were 14 unhealthy air days, while in 2005, there were 51 unhealthy days based on the current standard. The region has not experienced a more serious "Code Red" unhealthy air day since 2023.

Ozone levels are exacerbated by high temperatures, low wind, local emissions, pollution transported into metropolitan Washington from outside the region, and other environmental factors. In 2025, despite favorable weather conditions for increased ozone levels, the low number of exceedances suggests the region's air quality continues to improve year over year.

COG data shows that, in recent years, multiple contributing factors must be present to result in an ozone exceedance. Previously, just a few factors, such as a combination of high temperatures and low wind, could create high ozone conditions.

Poor air quality contributes to increased severity of heart and lung disease, aggravates respiratory conditions, and can be particularly dangerous to children, older adults, and individuals with underlying health conditions.

Based on current data, the region would meet federal ozone standards, determined by a 3-year average of the fourth-highest daily maximum ozone concentrations. Meeting this standard has been a longstanding priority for area officials at COG.

The region's air quality has improved thanks to actions by federal, state and local governments, area businesses, and community groups, such as regulations to reduce power plant and passenger vehicle emissions, programs to improve energy efficiency and renewable energy use, and the promotion and use of transit options like Metro.

The Metropolitan Washington Air Quality Committee, which is staffed by COG, coordinates air quality planning in the region. Its members include area elected officials, environmental directors, and state air management and transportation officials. COG provides air quality forecasts for metropolitan Washington. It also educates the public about voluntary actions people can take to reduce pollution and the health risks of bad air quality through its Clean Air Partners program, which is co-sponsored by the Baltimore Metropolitan Council.