New studies show strong links between wildfire smoke during the summer and health problems like flu or asthma later in the year.

“In 2021, almost half our days from June to September were affected by wildfire smoke last summer,” Montana Department of Environmental Quality air quality bureau chief Bo Wilkins told the Legislature’s Environmental Quality Council on Tuesday. “Our nice, green good-air-quality days are kind of gone.”

2021 was the fourth-driest on record going back 127 years, according to Montana State Forester Sonya Germann. The dry conditions contributed to 2,878 wildfires burning a total 953,000 acres across state, federal and private land. Of those, 96% were caught by initial attack firefighters and only 92 grew bigger than 100 acres.

Nevertheless, the ones that did escape initial attack were so serious, Montana was at Preparedness Level 5 for 42 days — the highest possible level indicating extreme fire risk and lack of firefighting resources. Germann said of the 3,962 requests for firefighting aircraft, agencies were unable to fulfill a third of the flights. And of the 1,472 ground crew requests, only 45% got filled.

“Those are significant numbers,” Germann said. The state’s 10-year average for firefighting expenses is $23.3 million. Last year, suppression costs hit $50.1 million, she said.

A new policy from the U.S. Forest Service released last week calls for more prescribed burning of public lands to reduce wildfire hazards, along with extensive logging and fuels reduction work. While prescribed burning produces smoke, it tends to contain fewer harmful toxins and particulates than large-scale wildfires. However, it extends the number of days communities might get smoky air each year.

Medical data from last year showed significant increases in emergency room visits in hospitals downwind from the Robertson Draw fire in Carbon County, the Harris Mountain fire in Cascade County and the Haystack fire in Silver Bow and Jefferson counties, according to research from Department of Health and Human Services chronic disease prevention supervisor Jessie Fernandes. Even after factoring for the surge in delta-variant COVID cases, the smoke-related cases of difficulty breathing or elevated heart rates were concerning, she said.

Professor Erin Landguth of the University of Montana’s Center for Population Health Research showed new studies linking summer smoke exposure to influenza cases later that winter. Cases go up 16 to 22% for every 1 microgram increase in smoke pollution, resulting in flu seasons three to five times worse than average following a bad fire summer.

Wildfire smoke contains particles 10 microns in diameter — small enough that a string of them would look like a pearl necklace around a human hair. But worse, there are particles just 2.5 microns around, which would form a necklace around those 10-micron bits. That particulate matter carries toxins like benzene and formaldehyde from burning forests deep into people’s lungs, where they aggravate health risks from heart disease to diabetes.

“Montana jumps out compared to other states,” George Washington University post-doctoral researcher Katelyn O’Dell said of the state’s deaths related to wildfire smoke exposure. Beyond that, the health impacts show up in people needing doctor visits, outpatient hospital services and asthma inhalers refilled.