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Explainer: Montana’s air quality ratings

Posted at 1:47 PM, Aug 04, 2018
and last updated 2018-08-04 15:47:46-04

Smoke continues streaming into Montana from wildfires burning in the western United States, causing hazy skies and increased health risks.

The Montana Department of Environmental Quality (DEQ) provides daily updates about wildfire smoke and air quality. While decreasing air quality often leads to hazy conditions, it can also present health risks.

The DEQ rates air quality based on the amount of particulate matter (PM) in the air, which is often caused by smoke from wildfires. In addition to being emitted from wildfires, PM can also come directly from other sources, such as construction sites, unpaved roads, fields, and smokestacks. The EPA says that PM is a mixture of solid particles and liquid droplets found in the air. Some particles, such as dust, dirt, soot, or smoke, are large or dark enough to be seen with the naked eye. Others are so small they can only be detected using an electron microscope.

The air quality ratings in Montana are assigned a color code. The color green, for example, means that there are no negative health effects, and no precautions are necessary for outdoor activity. 

On Thursday, August 2nd, the air quality was rated as "moderate" for the following areas: Billings, Bozeman, Broadus, Butte, Columbia Falls, Dillon, Frenchtown, Great Falls, Hamilton, Lewistown, Missoula, and Seeley Lake.

"Moderate" (yellow) means that there is the possibility of aggravation of heart or lung disease for people with cardiopulmonary disease, and the elderly.

Here are the other ratings, listed in order of increasing danger or health risks: 

  • Unhealthy for Sensitive Groups (orange): Increasing likelihood of respiratory symptoms in sensitive individuals, aggravation of heart or lung disease and premature mortality in persons with cardiopulmonary disease and the elderly. People with respiratory or heart disease, the elderly and children should limit prolonged exertion.
  • Unhealthy (red): Increased aggravation of heart or lung disease and premature mortality in persons with cardiopulmonary disease and the elderly; increased respiratory effects in the general population. People with respiratory or heart disease, the elderly, and children should avoid prolonged exertion; everyone else should limit prolonged exertion.
  • Very Unhealthy (Purple): Significant aggravation of heart or lung disease and premature mortality in persons with cardiopulmonary disease and the elderly; significant risk of respiratory effects in the general population. People with respiratory or heart disease, the elderly, and children should avoid any outdoor activity; everyone else should avoid prolonged exertion.
  • Hazardous (maroon): Serious aggravation of heart or lung disease and premature mortality in persons with cardiopulmonary disease and the elderly; serious risk of respiratory effects in the general population. Everyone should avoid any outdoor exertion; people with respiratory or heart disease, the elderly, and children should remain indoors.

The DEQ publishes a daily Wildfire Smoke Update; here is the update for Thursday, August 2nd: 

Hazy skies and generally MODERATE air quality continues to dominate the skies across Montana on Thursday morning. The Helena Valley saw conditions deteriorate to UNHEALTHY FOR SENSITIVE GROUPS late last night and has remained there throughout the morning. The source of all this smoke remains the same, intense fire activity in California and Oregon. The smoke from these fires has been carried up into Montana along a strong ridge of high pressure. Most of this smoke has remained above ground level, leading to very hazy skies but only MODERATE air quality in most places.

First the good news. 
The ridge of high pressure is expected to break down over the next 24 hours. A disturbance is expected to bring strong westerly winds to the state today. This wind should help push out much of the haze that has built up over the past week. We are already starting to see clearer air move into Northwest Montana this morning, where air quality recently improved to GOOD levels. The change in wind direction will also keep smoke from fires in Oregon and California to our south for the weekend. This should improve visibility across the region.

And now the bad news. 
The increased westerly winds, combined with a dry cold front has prompted red flag warnings from central Washington all the way to the North Dakota border, covering most of Montana. Conditions will be ripe for new fire activity both in Montana and upwind in Idaho, Washington, and British Columbia. While existing fire activity in Montana remains light, fires in southern British Columbia and Washington will likely send smoke our way throughout the weekend, possibly beginning later this afternoon. There is also a cluster of fires in northwest Montana that are having localized impacts to air quality near Eureka. Under red flag conditions, smoke from these fires may spread further into northern Montana. Another ridge of high pressure is expected to build over the western U.S. starting on Monday and persisting through much of next week. This will likely bring the overhead haze back to Montana.

What does this mean for air quality? 

Expect the hazy skies and MODERATE to UNHEALTHY FOR SENSITIVE GROUPS air quality to improve from the northwest to southeast throughout the day. Some areas may see air quality get briefly worse later this afternoon when the increasing winds help mix the overhead smoke down to the ground level. By tomorrow morning, most areas should see improvement in the hazy skies. While visibility will improve in most areas, increasing fire activity in the Pacific Northwest will likely keep smoke present in Montana through the weekend. Northwest Montana could see smoke from these fires as early as this afternoon. Any smoke that does move over the state will be more likely to reach the ground level, but elevated concentrations will likely be more localized under the plumes than the widespread impacts that we have seen this week.