Poor air quality with high levels of tiny pollution particles known as PM 2.5 are tied to a spike in emergency department visits for heart- and lung-related illnesses and stroke, a California study suggests.

Based on analysis of areas affected by the intense 2015 California wildfire season, researchers found that within a day of residents being exposed to dense smoke, emergency room visits for heart attacks and other cardiac events and symptoms rose by 15 percent overall, and 42 percent among people over age 65.

Stroke and other cerebrovascular emergencies rose 17 percent overall, and 22 percent for older adults, the study team reports in the Journal of the American Heart Association.

“Wildfires have become a leading cause of short-term exposure to polluted air,” said Ana Rappold of the U.S. Environmental Protection Agency’s National Health and Environmental Effects Research Lab. “It’s important to talk to people about how exposure to wildfires can impact their health.”

Wildfire smoke contains several pollutants, including carbon monoxide, nitrogen dioxide, and ash particles that have been associated with lung and heart problems.

It also contains tiny particles, smaller than 2.5 micrometers, that are produced in indoor cooking fires and motor vehicle exhaust as well. These particles are small enough to enter the bloodstream from the lungs and are linked to inflammation, heart rhythm disturbances, and clotting issues.