EPA signed its final national ambient air quality standards (NAAQS) for carbon monoxide (CO ) on August 12, 2011. In the rule, EPA concludes that the current primary standards are sufficient to protect public health and retains those standards. The agency also concludes that no secondary standard should be set for CO at this time. The rule revises monitoring provisions in the current standards so that states will have to monitor near roads in heavily populated areas, and it requires states to place monitors in areas with more than 1 million people. EPA notes that CO levels have dropped by 80 percent since 1980 because of emissions controls on vehicles, the largest source of CO . No areas in the United States currently violate the standards. The final rule will be effective 60 days after its publication in the Federal Register.