There are about 154 million Americans pose a threat to their health due to air pollution, according to American Lung Association (ALA).

Around 48 percent of U.S. residents live in counties where smog (ozone) is too high, 20 percent live in areas where there are too many short-term spikes in pollution and six percent live in areas with harmful year-round soot (particle pollution), said the report.

California is listed in the report as the most polluted state, where people are breathing some of the worst air.

The air is so polluted in some areas that it is often dangerous to breathe, the ALA said in its annual report on air quality across the United States.

About 17 million Americans live in areas afflicted by all three air pollution hazards, the report noted.

Compared with other states, California has more polluted places, including Los Angeles, Long Beach, Riverside, Bakersfield and Fresno, the report said.

Honolulu in Hawaii and Santa Fe-Española in New Mexico are the only two cities in the nation that had no days in which smog and soot levels reached unhealthy ranges, making them the cleanest cities in the nation, said the report.

Research suggests air pollution threatens human health. Small particles of pollution can lodge deep in the lungs and can damage blood vessels and the heart, according to Dr. Norman Edelman, the ALA’s chief medical officer.

Pollution can also contribute to low birth weights, diabetes, cardiovascular disease, heart attack, stroke and, ultimately, shorter life spans, said Michael Jerrett, a professor of environmental health sciences at University of California, Berkeley’s School of Public Health.