The times are rapidly changing — for the better, at least — in terms of ozone pollution for the greater Los Angeles metropolitan area.

But despite improvements, the Los Angeles-Long Beach-Riverside region is the top ozone polluted area in the country, according to the American Lung Association’s State of the Air 2016 report released Wednesday.

For this survey, Los Angeles, San Bernardino, Riverside and Orange counties are lumped together as the Los Angeles metro area, said Maria Bernabe, a American Lung Association spokeswoman.

San Bernardino County registered as the worst of the lot, with 153 unhealthy ozone days, down from 203 in 2005. Nevertheless, it still received “F” grades for ozone and two types of particle pollution.

Los Angeles County registered 109 unhealthy ozone days, down from 159 in 2005; while Riverside County had 140, down from 191 in 2005; and Orange County recorded nine, down from 38 in 2005.

These three counties also received “F” grades for ozone.

Pollution readings from 2012-2014 form the basis of the 2016 air report.

Although many California metro areas are listed among the top 10 worst for air pollution nationally, some of those had their cleanest year yet for ozone or particle pollution, including Los Angeles, which saw its lowest air pollution levels in the 17 years of the State of the Air report, said Olivia J. Diaz-Lapham, president and CEO of the American Lung Association, during a news conference Tuesday.

The Southern California region has seen a 90 percent reduction in unhealthy particle pollution over the history of the report, the association said.

“Thanks to California’s cleaner vehicles and fuels and other innovative clean air policies, we’re seeing steady progress in our fight for cleaner air,” Diaz-Lapham said.

Nevertheless, more than 80 percent of Californians — 32 million residents — still live in counties with unhealthy air during certain parts of the year. And over 17 million Californians live in counties that received three failing grades in State of the Air 2016, the association said.

We simply must do more to protect Californians,” Diaz-Lapham said.

Climate change and global warming could erode some of the gains, by creating an environment more favorable to ozone formation and blowing dust, the association warned.

The association says Californians must continue to invest in zero-emission vehicles, cleaner freight transport, renewable power, more sustainable community planning and cleaner alternatives to wood burning.

At-risk populations include children, seniors, those with asthma, chronic obstructive pulmonary disease, heart disease, diabetes and low-income communities, the association said.

Air pollution can cause asthma, heart disease and retard the development of lungs in children, officials said.

Major improvements have occurred in particle pollution as well for the Los Angeles metro area, the report showed. In Los Angeles County, there were just eight unhealthy particle days in the 2016 report, down from 84 in 2004.

San Bernardino County posted nearly 25.9 unhealthy particle days in the 2004 report, while there were just 12.8 in the most recent one.

Nevertheless, Los Angeles received a “fail” under a pass/fail grading system.

Riverside County had 11 unhealthy particle days in the report released today, down from 107 in 2004. That also was a “fail.”

Orange County passed with its four unhealthy particle days in 2016, down from 41 in 2004.