Take a big breath, Naples.

The city tops realtor.com's list of the least-polluted cities in America.

To determine where the air is pristine and the water is safe to drink, the website ranked the 10 largest metros based on the following factors:

» Toxic chemicals released from factories

» Greenhouse gas emissions per square mile

» Number of Superfund sites per square mile

» Air quality, determined by the number of clear days in a year

» Water quality, measured by contaminants such as lead, copper and arsenic

Florida leads the way in air quality, and Naples is the cleanest city in the state, helped by its natural surroundings, which include the Everglades, Ten Thousand Islands and Corkscrew Swamp Sanctuary.

"Collier County has more acres of protected lands than any other county in Florida," Renee Wilson, a spokeswoman for the Rookery Bay National Estuarine Research Reserve, told realtor.com, pointing out that's mostly due to the wetland characteristics of the Everglades.

The No. 1 ranking didn't come as a big surprise to Dominic Pallini, president of the Naples Area Board of Realtors and broker/owner of Vanderbilt Realty of Naples.

"Our state and local government (Collier County) work hard to make Florida, Naples especially, the cleanest and safest place in the country. It makes Naples a prime location to purchase a home," he said in an email.

Ranking as the second-cleanest city? Salem, Oregon. Realtor.com tipped its hat to the state for becoming "the first in the nation to pass a law to phase out coal completely, requiring its largest utilities to supply at least half of their electricity from renewable resources, like wind and solar, by 2040."

In Salem, many residents bike or walk to work, and the city "didn't have a single day with bad air last year," according to realtor.com, which based that conclusion on data from the U.S. Environmental Protection Agency.

The third least-polluted city is also in Florida: Ocala, which realtor.com describes as "tucked in Central Florida's horse country" with "a glorious 673 square miles of vegetation" and offering "crystal-clear" water in Silver Springs.

Rounding out the top five cleanest cities: Anchorage, Alaska, at No. 4 and Santa Rosa, California, at No. 5.

Realtor.com points out that pollution in the U.S. has declined noticeably in recent years, adding that the nation's industrial plants released 25 percent less toxic chemicals in 2015 than in 2005. An EPA spokesman told the website the credit goes to green chemistry, better waste management and fewer facilities.

Topping the list of the dirtiest cities is Philadelphia, "where crude-oil trains chug through like clockwork" and "plumes of white smoke from oil refineries can be seen and sniffed from most residents’ backyards," according to realtor.com.

In the city, 13.4 million pounds of poisonous chemicals were released in 2015 by oil refineries, shipyards and auto manufacturers, the EPA reported.

For more information, see realtor.com/news/trends/most-polluted-and-least-polluted-cities.

The Rankings - Best and Worst

America's Top 10 cleanest cities

1. Naples, Florida

2. Salem, Oregon

3. Ocala, Florida

4. Anchorage, Alaska 

5. Santa Rosa, California

6. Ann Arbor, Michigan 

7. Eugene, Oregon

8. Little Rock, Arkansas

9. Salisbury, Maryland

10.Salinas, California

America's Top 10 dirtiest cities 

1. Philadelphia, Pennsylvania

2. Los Angeles, California

3. Houston, Texas

4. New York, New York

5. Chicago, Illinois

6.  New Orleans, Louisiana

7. Reading, Pennsylvania

8. Salt Lake City, Utah

9. Baton Rouge, Louisiana

10. Milwaukee, Wisconsin