Air pollution is a problem in places like China, Singapore and Mexico. U.S. government efforts have caused a sharp drop in air pollution in large American cities over the past several decades. However, those efforts have not yielded much in some large cities, many of which are in the central valley of California.

Realtor.com said of air quality in U.S. cities:

The Environmental Protection Agency tracks pollution in 500 urban areas with its Air Quality Index—a measure of sulfur dioxide, carbon monoxide, nitrogen dioxide, and ozone levels. It then rates the air quality on a spectrum from “good” to “hazardous.”

With the aid of 2015 EPA data, we ranked the 100 largest metropolitan areas (including their surrounding suburbs and counties) by the percentage of days with good air quality to come up with a list of the nation’s top 10 cities with the cleanest air and, of course, the other end of the spectrum.

Among the 10 cities with the worst air pollution were Riverside, Bakersfield and Los Angeles in California. Polluted air tends to get trapped in central California, probably because of the mountains.

Most of the remaining cities with the worst air pollution are among America’s biggest cities. Aside from Los Angeles, these include New York, Chicago and Philadelphia. Others are among the old-line industrial cities — Cleveland and Pittsburgh. Rounding out the 10 worst air cities are Phoenix and Kansas City.

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The other end of the list, the cities with the cleanest air, includes cities along the oceans. Five are in of Florida, either on the Atlantic or inland near Orlando: Palm Bay, Daytona Beach, Orlando, Lakeland and Cape Coral.

The top city, Honolulu, is obviously surrounded by ocean. Rounding out the cleanest air list are Boise, Idaho; Kansas City; Durham, N.C.; Wichita, Kan.; Colorado Springs, Colo.; and Durham, N.C.

Since size and geography determine many of the cities on the two lists, nothing is likely to make the list change.

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