The Montana Department of Environmental Quality (MTDEQ) is urging residents to stay indoors until air quality improves, as smoke from wildfires has created a poor living environment for vulnerable populations in parts of the state.

According to a webpage from the MTDEQ, air quality in Broadus, a city in eastern Montana, rose to unhealthy levels Tuesday morning. Unhealthy air quality levels occur when the air quality index (AQI) is measured between 151 and 200. Poor air quality was noted in western Montana on Monday, prompting MTDEQ officials to issue an air quality advisory.

The air quality advisory in western Montana was in effect for Beaverhead, Deer Lodge, Granite, Lake, Mineral, Missoula, Ravalli, Sanders and Silver Bow counties, according to a report from the National Weather Service (NWS). The air quality advisory is expected to remain in effect until 4 p.m. local time on Tuesday due to elevated particulate matter levels from wildfire smoke, the advisory said.

On Monday afternoon, particulate matter levels were measured ranging from “moderate” to “very unhealthy” in the affected areas.

“When air quality is very unhealthy… state and local health authorities advise that people with respiratory or heart conditions, the elderly, and children should avoid all outdoor activities; all others should avoid prolonged exertion,” the warning said.

The warning will be updated Tuesday afternoon. MTDEQ measurements on Tuesday showed that air quality had improved across much of western Montana, although some areas in eastern Montana, such as Broadus, still showed concerning levels.

Summer wildfires are a major contributor to Montana’s poor air quality, according to the MTDEQ website. Several wildfires are burning in Montana, according to a map from the Fire, Weather and Avalanche Center. Although smoke can travel for miles, NWS meteorologist Luke Robinson said Newsweek that the smoke causing poor air quality in Montana this week came from local fires.

Robinson said smoke will continue to linger in the region this week, though wildfire activity will determine how thick the smoke is. Other weather threats Tuesday included isolated showers and thunderstorms in western Montana with the potential to produce winds as high as 40 mph.

According to the MTDEQ, Montana’s wildfire season runs from April through October.

People who are sensitive to unhealthy air quality, such as children and the elderly, should limit their exertion when values ​​fall into the ‘unhealthy for sensitive groups’ category.

According to the United Nations Children’s Fund (UNICEF), young children are more sensitive to air pollution because, among other things, they breathe faster than adults.

“Children are physiologically more vulnerable to air pollution than adults because their brains, lungs and other organs are still developing,” according to a UNICEF website. “Some air pollutants can cross the placenta and affect developing babies. Air pollution can also affect lung function and development, which continues into adolescence.”