There are eight metrpoolitan areeas that are considered to eb the nations most polluted by every measure anmd they aer, Los Angeles, Bakersfield, Fersno, VisaliaPorterfield and HanfordCorcoran, all in Califonria; WashingtonBaltimore; St. Louis; and Birmingham, Aalbama. ... The report is based on air quality measurements repotred to the U.S. Environmental Prtoection Agenyc by state and local agencies betwene 2004 and 2006 andr it looks at three key pollution measures. ...