California real estate is among the most valuable in the land, but to cash in you may have to breathe in some of the foulest air in the land.

Five metropolitan areas in the Golden State have the nation's brownest air, according to "Clearing The Air 2003: Public Health Threats From Cars And Heavy Duty Vehicles," recently released by Surface Transportation Policy Project (STPP).

STPP, a nationwide network of more than 800 organizations devoted to improving the nation's transportation system, ranked metropolitan areas by the number of days of unhealthy air pollution levels over the last three years, based on data from the U.S. Environmental Protection Agency.

"Our study shows air pollution continues to be a serious health problem and transportation sources are a significant part of that problem. The public deserves a federal transportation program that lowers their exposure to unhealthy air and delivers transportation choices beyond simply having to turn an ignition key" said Anne Canby, president of the Washington D.C.-based STPP.

Among the largest metropolitan areas, California cities topped the list with 445 bad air days in the Riverside-San Bernardino area -- averaging nearly 150 days a year -- followed by, Fresno, 421; Bakersfield, 409; Los Angeles-Long Beach, 255 and Sacramento, 163. Rounding out the Top Ten Cities with the most unhealthy air days were Pittsburgh, PA, with 134; Knoxville, TN, 109; Birmingham, AL, 100; Houston, TX, 94 and Baltimore, MD with 93 unhealthy air quality days over the three-year period.

Clean air cities included Bergen-Passaic, NJ, with no unhealthy air days during the three-year period; Jacksonville and West Palm Beach-Boca Raton, FL, both 1 day; Miami, FL, 4; Minneapolis-St. Paul, MN-WI, 5; Fort Lauderdale, FL, 8: Las Vegas, NV-AZ, 9; Oklahoma City, OK and Orlando, FL, both 10 and Austin-San Marcos, TX, 11 unhealthy air quality days.

Scientific studies link air pollution to asthma, heart and lung disease and certain cancers among a host of ailments and half of all Americans -- 133 million -- often breathe unhealthy air.

The STPP study says transportation is a major contributor to air pollution nationwide, at a time when some federal legislators want to roll back clean air protections and cut funding for transportation and transportation fuel alternatives.

Unfortunately, when you consider other environmental toxins -- industrial plant exhaust, pesticides from farms and lawns, as well as exhaust from passenger vehicles, few cities offer low levels of toxic exposure, according to "Healthy Cities," produced for Organic Style magazine by Robert Weinhold, author of the book "Rating Guide to Environmentally Healthy Metro Areas" (Animas)" a more comprehensive report.

To produce a list of the most and least healthy towns based on air quality, toxic releases and agricultural pollution, Weinhold analyzed data from 125 cities.

"A range of estimates suggest that the environment plays about a 10 to 20 percent role in determining your health. No city has low levels of exposure, but some areas are much better than others," said Weinhold.

Top ranked were Santa Fe, NM; Rapid City, SD; Grand Junction, CO; Olympia, WA; Fort Myers, FL; Sherman, TX; Cheyenne, WY; Flagstaff, AZ; Columbia, MO; and Anchorage, AK.

With California cities noticeably missing, the bottom 10 were Indianapolis, IN; Cincinnati, OH; Pittsburgh, PA; Washington, D.C.; Philadelphia, PA; Cleveland, OH; New York City, NY; Detroit, MI; Chicago, IL and, the very worst, St. Louis, MO.

How do you avoid so many unhealthy locations?

Head for the hills.

Weinhold says airborne pollutants tend to accumulate in valleys, so the higher up you live, the fewer pollutants you'll breathe.

Likewise, you can breathe cleaner air if you can determine the direction of prevailing winds and move upwind, away from the pollution drift from airports, landfills, industrial plants and the like.

Weinhold also says living upstream from industrialized and agricultural areas will give you a better shot at cleaner water.