The U.S. state of California experiences far more days with poor air quality each year than the rest of the country, and this trend could worsen over the next 30 years due to the increasing incidence of wildfires and extreme heat events, according to a new study.

Climate change impacts, such as extreme heat, drought, and wildfires, are contributing to the rise in pollutant levels in California, undoing the progress in air quality that the state had achieved through regulations and policies in past decades. This information comes from a report released by the First Street Foundation, a research and technology nonprofit, on Monday.

Across the United States, over 83 million people, more than 25 percent of the population, are exposed annually to unhealthy air quality, and 1.5 million are at risk of experiencing "hazardous" air quality today.

To better understand air quality levels across the United States, the researchers developed computer models to simulate PM 2.5 and ozone levels.

Scientists believe the two pollutants are most clearly linked to climate change. PM 2.5 is emitted from increasing wildfire smoke, and higher ozone levels are generally associated with higher air temperatures.

Fine particles in the air, known as PM 2.5, travel deep into the lungs and can cause diseases such as cancer. PM 2.5 levels have generally dropped across the country since 2000, but the trend has reversed recently, especially in the country's west because of wildfire smoke.

Over the next 30 years, the population exposed to "unhealthy" air quality days is expected to increase by 51 percent, while the population exposed to "hazardous" days is expected to increase by 27 percent, according to the report.

The most persistently impacted areas of the country are in the west, where the number of days with poor air quality increased nearly two times compared to the beginning of the century.

The researchers said California had been most affected by the rising fine particle pollution, driven by more intense and frequent wildfires.

Places like California's Central Valley, the San Francisco metro area, and much of Southern California are all expected to experience up to 90 days of poor air quality in a bad year.

In the future, major metro areas like Seattle in Washington and Portland in Oregon are expected to see nearly two additional weeks of poor air quality due to increasing wildfires in the region, the report said.

The report adds evidence to previous studies examining pollution trends in the United States.

A study published in The Lancet Planetary Health in December found wildfires in the United States have caused a decline in air quality and an increase in deaths in parts of the country - even though air quality had been improving.

The study, using data on air pollution and related deaths in the United States between 2000 and 2020, revealed that air pollution started worsening again in 2010 in the wildfire-prone West, with California seeing the highest levels of air pollution.

(Cover image via CFP)