Faced with a lawsuit by 15 states, the U.S. Environmental Protection Agency announced this week it would no longer delay the implementation of a rule requiring states to reduce emissions of smog-creating air pollution. Crafted by the Obama administration in 2015, the regulation calls for states to begin meeting stricter ozone standards as of October 1, 2017, lowering the air pollution limit from 0.075 parts per million to 0.070 ppm. Ground-level ozone, or smog, is created when pollutants from cars, power plants, and other common industrial activities react with sunlight. It can cause respiratory and other health problems. In June, U.S. EPA head Scott Pruitt announced the agency would delay implementation of the new standards by one year.