According to a recent survey, residents of Portland, Ore., live in the cleanest city in the United States. Reader's Digest editors scored each of America's 50 largest cities on air quality, water quality, industrial pollution (toxics), Superfund sites, and sanitation. The study looked at the metropolitan areas surrounding the cities, not just the cities themselves. Each earned points on a scale from 1 to 50 in each category, with the numbers reflecting a city's ranking in comparison to the other places; the cleanest city in any category received 50 points. Next, the editors weighted the five categories in terms of the health threat each one posed relative to the others, further adjusting for cities with no available sanitation data. For example, water and air scores received twice the weight of sanitation scores. For the final number, they averaged all the points for each city.

America's cleanest, dirtiest cities

A recent Reader's Digest study ranked the nation's 50 biggest cities based on air and water quality, pollution, Superfund sites, and sanitation. For a complete list, visit www.rd.com. Source: Reader's Digest