More than 28 million California residents – or about 70 percent of the state’s population – live in counties with unhealthy air, according to a report published last week by the American Lung Association (ALA).

According to the ALA State of the Air Annual Report 2015, California’s pollution problems are primarily caused by emissions from transportation sources, including cars, diesel trucks and buses, locomotives, ships and agricultural equipment, and other sources including oil refineries, manufacturing plants, residential wood burning and wildfires.

Weather conditions, heat and geography also facilitate smog and soot formation in California. Ongoing drought weather conditions are contributing to worsening particle pollution in many areas of the state including Visalia, Bakersfield, Sacramento, Modesto-Merced, El Centro, San Jose-San Francisco and San Luis Obispo.

Despite these rankings, the report also shows that many California cities made significant improvements in reducing unhealthy ozone and particle pollution over the history of the report. Major regions of the state have seen reductions in unhealthy ozone days of approximately 40 percent or more since the 2000 report, led by 80 percent or more reductions in bad air days in the Bay Area and San Diego regions. Five cities reached their lowest levels (Los Angeles, Visalia, Bakersfield, Sacramento and San Diego).

This year, the American Lung Association in California launched Doctors for Climate Health, a social media campaign featuring leading physicians (including California Medical Association members) highlighting the critical health impacts of climate pollution on Californians’ health today, as well as for future generations.

Click here for more information and to read the report.