Metropolitan Statistical Areas
Report Card: What's the Grade for Your Air?
County rankings and cleanest county lists are also available in the full report.
Metropolitan areas were ranked by the highest weighted average among the counties within a given Metropolitan Statistical Area as of 2013 as defined by the White House Office of Management and Budget (OMB). MSA and CSA are terms used by the U.S. Office of Management and Budget for statistical purposes. MSA stands for Metropolitan Statistical Area and includes one or more counties. CSA stands for Combined Statistical Area and may include multiple MSAs and individual counties.