The United States has its own set of emissions standards that all new vehicles must meet. In the United States, emissions standards are managed by the Environmental Protection Agency (EPA). Under federal law, the state of California is allowed to promulgate more stringent vehicle emissions standards (subject to EPA approval), and other states may choose to follow either the national or California standards. California had produced air quality standards prior to EPA, with severe air quality problems in the Los Angeles metropolitan area. LA is the country's second-largest city, and relies much more heavily on automobiles and has less favorable meteorological conditions than the largest and third-largest cities (New York and Chicago).