MADISON, Wis. – The Wisconsin Department of Justice (DOJ) secured a legal victory after a court issued a decision requiring the U.S. Environmental Protection Agency (EPA) to move forward with implementation of a rule strengthening national ambient air quality standards (NAAQS) for fine particulate matter, commonly known as soot.

“Air quality impacts people’s health and quality of life,” said AG Kaul. “The Trump administration should stop trying to block progress toward cleaner air.”

Wisconsin DOJ and a coalition sued the EPA in April over its failure to implement the rule. In its decision this week, the U.S. District Court for the Northern District of California granted the coalition’s motion for summary judgement, denied the EPA’s motion to pause the case, and rejected the agency’s other arguments against the coalition’s lawsuit.

Soot is an air pollutant emitted from a variety of sources including combustion-engine vehicles, factories, and construction sites. Because of the particles’ small size, once inhaled, they can penetrate the lower parts of lungs, move out of the respiratory system, and affect other organs. As a result, soot exposure can lead to myriad health problems, including shortened lifespans, heart attacks, asthma attacks, and cancer.

Under the Clean Air Act, EPA is required to set NAAQS for several pollutants, including fine particulate matter, at a level that protects public health and welfare. When NAAQS are updated, the Clean Air Act gives EPA a specific deadline to designate areas of the country that are in violation of the updated standard as “nonattainment.” This designation provides key support for state programs to reduce dangerous pollution levels to safer levels. EPA ignored this deadline, leading to the multistate suit, and the court decision requires EPA to issue the designations.

Reductions in soot are associated with decreases in the risk of mortality and increases in life expectancy. In 2024, EPA strengthened the soot NAAQS based on overwhelming scientific evidence. According to its own estimates, EPA has reported that the first year alone of full attainment of the 2024 NAAQS will result in significant public health benefits, including avoiding 4,500 premature deaths, 2,000 emergency room visits, 5,700 new cases of asthma, 800,000 cases of asthma symptoms, 290,000 lost workdays, and 1,000 hospital admissions for Alzheimer’s/Parkinson’s diseases. The value of these and other health benefits would outweigh the estimated costs of implementation by $46 billion.