Current Air Quality and Restrictions:

Click here to check the most recent PM2.5 concentrations in Missoula, Frenchtown and Seeley Lake on Montana's Today's Air website!


Air quality in Missoula County is Good to Moderate   If air quality becomes Unhealthy for Sensitive Groups or worse this web page will be updated. Check the Today's Air website (link in box above) for the most current PM2.5 measurements across the state.

 Activity guidelines for schools, sporting events and day cares

Flyer about HEPA filters

Flyer about central air filtration

August 25, 2018 10:00 AM 

Improved air quality is possible starting on Sunday as a weather system with potential rain and change in transport wind direction starts to move through the area.  Wind direction may shift so that Missoula County is not downwind from as many fires for the beginning of the week.

August 24, 2018 9:00 AM 

Smoke from yesterday evening stuck around all night and we woke up to smoky skies this morning.  Conditions have been holding steady at Unhealthy for Sensitive Groups in most of Missoula County (Seeley Lake has been generally keeping to the upper edges of Moderate, but there’s still a lot of overhead smoke in the area.)  Cloud cover made this morning particularly dismal, but despite appearances, we haven’t tipped into Unhealthy air quality quite yet.  Of course, for a lot of folks – mainly the elderly, children and anyone with heart or lung disease, this is unhealthy air.  Fun smoke fact: roughly 30% of the population falls into the Sensitive Groups category.  That’s a lot of folks.  So even if you’re all hunky dory with the smoke in the area, understand a lot of people are likely being affected.  Wildfire smoke season is always a great time of year to treat each other with a little bit of extra kindness.

When air quality is Unhealthy for Sensitive Groups, people with heart or lung disease, children and the elderly should limit prolonged outdoor exertion.  Anyone experiencing symptoms of heart or lung disease associated with smoke exposure should contact their health care provider.

We’re currently coping with the remnants of the smoke plume that rolled over our area yesterday evening as well as some smoke being pulled into our area by southwesterly flow aloft.  The direction of our overhead winds is going to shift in the next few hours and that will put us, once again, downwind of the fires in Washington and British Columbia.  If you check out the satellite photo, you’ll see there’s a glorious gap of clean air between our current smoky air and the Washington smoke.  As our weather shifts throughout the day, there’s a good chance we’ll see some nice smoke clearing as that area of clean air moves overhead.  However, it will be closely followed by more smoke.  Strong winds and general atmospheric turbulence from a passing weak cold front may keep the smoke at bay for a few additional hours this afternoon, so pay attention to changing conditions and run outside quick like a bunny when the air clears! 

If we do get some of that sweet, sweet clean air, it will unfortunately be short-lived.  The Washington and Canadian fires are still going gangbusters, and the overhead winds are going to deliver that smoke for at least the next few days.   

Our overhead smoke was sent our way from fires to our southwest.  Later today we will see Washington smoke swing toward us and then keep heading our way for the next few days.  Happily, there’s a gap of clean air that is likely to roll over Missoula County as the winds shift.  That will be nice.  Source: CIRA and NOAA

082418_AM color satellite photo showing smoke over the western U.S.

August 23, 2018 5:00 PM

Well, it took longer than I expected, but the wall of smoke finally arrived in Missoula.  Our air quality in Missoula County is currently Unhealthy for Sensitive Groups.  While the smoke trudging its way across the state led rapid air quality deterioration across Western Montana, the good news is that the smoke plume is relatively thin and is moving at a good clip.  This will limit the amount of smoke that ends up on the valley floor.   The thick overhead smoke will be out of our area soon, but it will likely leave substantial haze in its wake and I’m not expecting any dramatic air quality improvement this evening.  When the smoke rolled over Thompson Falls, air quality hit Unhealthy for Sensitive Groups and stayed there. We’re likely to see some smoke stick around this evening and into Friday morning.  (Also, there’s just a lot of smoke in the area – even without the big old plume there’d be substantial overhead haze.)

When air quality is Unhealthy for Sensitive Groups, people with heart or lung disease, children and the elderly should limit prolonged outdoor exertion.  Anyone experiencing symptoms of heart or lung disease associated with smoke exposure should contact their health care provider.

For Friday, we’ll continue to be downwind of the fires in Washington, but a weak cold front may provide a reprieve from the smoke. 

Check Montana’s Today’s Air website for near real-time air quality conditions around the state: Today’s Air.

Oh, hello smoke.  The smoke plume responsible for the sudden air quality grossening (if it’s not a word, it should be) has been slowly making its way across the region all day.  Source: CIRA and NASA

082318_PM color satellite photo of smoke

August 23, 2018 11:00 AM

We’ve seen a return of smoky skies today thanks to overhead winds drawing smoke from Western fires back into Montana.  Conditions are currently Moderate throughout Missoula County, but may degrade later today as more smoke moves into the area.  Based on current trends, we’re likely to hit Unhealthy for Sensitive Groups by noon.

When air quality is Unhealthy for Sensitive Groups, people with heart or lung disease, children and the elderly should limit prolonged outdoor exertion.  Anyone experiencing symptoms of heart or lung disease associated with smoke exposure should contact their health care provider.

There’s a thick band of smoke headed for us, and if it makes landfall, conditions may deteriorate even further. At its current pace, I expect it to be overhead around 1 p.m. (Note that there’s a chance it will stay overhead.  However, its arrival looks to correspond with the time our atmospheric mixing reaches higher elevations.  This means there’s a chance some of the overhead smoke will be pulled down into our breathing space.  High pressure is keeping atmospheric mixing heights relatively low, so we *might* not pull that overhead smoke down into the valley, but I’m not comfortable saying the band of smoke won’t impact our breathing space.)

Westerly flow will keep us downwind of fires for the next several days, and a brief high pressure ridge will keep the smoke in our valleys through today and into Friday.  There’s a bit of a weather disturbance that will roll through the area Friday evening, producing strong winds and a potential break from the smoke.  However, we will still be downwind from a lot of fires, so any break will be short-lived. 

The National Weather Service (NWS) has been talking up a significant weather system moving through the area on Sunday and into Monday.  If it arrives with all the bells and whistles in the original forecast, we’re looking at significantly cooler temperatures and the potential for widespread precipitation.  This will be super groovy if it happens.  Locally, it will mostly mean a lessening of fire danger.   The NWS has backed off the original forecast a bit since yesterday, but we’re still seeing some cooler temperatures and potential precipitation in the forecast. I’ve had a lot of people ask me it means the smoke is going to go away.  I don’t think it means the smoke is going to go away or fire season is going to end.  This is because most of our smoke is coming from fires burning in British Columbia and Washington.  As a savvy consumer of forecast discussions, I looked up the weather forecast in that area, and the NWS meteorologists covering that zone are sending out a far less rosy forecast.  Currently, they’re only expecting the massive weather system to drop precipitation over the Idaho panhandle and Montana.  The fires sending us smoke are mostly going to see cooler temperatures.  Cooler temperatures will help with firefighting efforts, but they won’t put the fires out. 

We’re going to be downwind of fires for several days.  Expect continued hazy skies and intermittent smoke impacts. 

I’ve attached some resources to this email (the ones I thought I attached to my last update but then forgot).  Please pay attention to changing conditions and, if you are able, spend time in clean air to give your system a break from the smoke.   

There’s a lot of smoke covering western Montana in this morning’s satellite photo.  You can also see the thick band of smoke headed our way.  It’s currently marching across Idaho and will be likely be overhead in a couple hours.  If its arrival corresponds with the time in the afternoon when our atmospheric mixing heights peak (and right now, according to models and my super primitive estimation of the smoke’s arrival) it lines up nearly perfectly), some of that smoke may end up in our valleys and air quality will deteriorate. Source: CIRA and NOAA

082318_AM color satellite photo showing smoke over the Northwestern United States.

August 20, 2018 8:00 AM

Yes, the air is bad.  No, the smoke is not the entire reason it is so very dreary out there.  We are dealing with a combination of cloud cover and smoke cover, which means the sky is gray and the light we can see is filtered through the smoke and is therefore extra weak.  Smoke is basically the sun’s kryptonite.  I could get into a whole narrative about how the smoke is the product of the sun’s unrelenting heat on the landscape and it has risen (literally) from the ashes to challenge its creator, but really.  That would be silly. 

Anyway.  Air quality is currently Unhealthy in Missoula and Seeley Lake.  Air quality is Unhealthy for Sensitive Groups in Frenchtown but is currently on a worsening trend and is edging toward Unhealthy.

When air quality is Unhealthy, people with heart or lung disease, smokers, children and the elderly should limit heavy or prolonged exertion and limit time spent outdoors.  People with asthma should follow their asthma management plan. People experiencing symptoms of heart or lung disease associated with smoke exposure should contact their health care provider. 

When air quality is Unhealthy for Sensitive Groups, people with heart or lung disease, children and the elderly should limit prolonged outdoor exertion.  Anyone experiencing symptoms of heart or lung disease associated with smoke exposure should contact their health care provider. 

As the smoke season drags on, we're likely to see more Unhealthy air quality make its way into our valleys.  Also, the longer we're in the smoke, the worse it is for everyone.  Please pay attention to how your body is reacting to the smoke and take precautions such as limiting outdoor exertion and taking steps to clean your indoor air.  I’ve attached some handy dandy guidance to this email. 

The next several hours could be somewhat interesting.  We’re already seeing the strong easterly surface winds in Missoula that were in this morning’s forecast.  Meanwhile, there’s a string of clouds coming at us from the southwest that is dropping some precipitation in our area.   And on top of that, we have slow moving winds swirling high overhead and generally keeping out-of-state smoke in our vicinity.  The strong surface winds this morning haven’t been able to scour the valleys clear, which isn’t terribly surprising when you consider the amount of smoke that rolled in over the area yesterday.  If we’re lucky, afternoon convection and the incoming weather system will be sufficient to lift the smoke up and out of our breathing space this afternoon.  However, I have a suspicion that there’s enough smoke overhead to keep us from seeing any significant relief from the haze today. 

Looking toward the future, the high elevation winds that are currently coming from the southwest are going to switch direction by tomorrow and come at us from the northeast.  You know, the exact same direction the wind’s been dumping smoke all day.  There aren’t a ton of fires to our northeast, but there will likely be some old smoke out there that is going to be pulled back into our region on Tuesday.  Over the next several days there’s going to be some general high-level wind swirliness happening over Missoula, and the air is going to come at us from many different directions.  I have a suspicion that this may just mean the overhead smoke gets pushed and pulled and generally stays in our area and, to spice things up, we’ll see an occasional influx of new smoke.  However!  There’s also a possibility we’ll catch a break and we’ll see clean air delivered to our valleys.  It’s just so very swirly and it’s hard to say precisely where the smoke from fires burning in Canada, Washington, Idaho, Oregon and California is going to end up. 

Stay up to date with changing smoke conditions by checking Montana’s Today’s Air website for near real-time PM2.5 concentrations around the state:

August 19, 2018 5:30 PM

As of 5:30 PM on Sunday Air Quality is Unhealthy for Sensitive Groups in most of Missoula County with air quality expected to fluctuate between Moderate and Unhealthy through tonight.

When air quality is Unhealthy for Sensitive Groups, people with heart or lung disease, children and the elderly should limit prolonged outdoor exertion.  Anyone experiencing symptoms of heart or lung disease associated with smoke exposure should contact their health care provider.

While wildfire smoke concentrations came down a bit this afternoon, smoky conditions from wildfires in Oregon, Washington, Canada, Idaho and Montana  are expected to continue.  Chances of good air quality are not good over the next several days.  So even people who have not felt any impacts from the smoke so far may start to feel some affects from the smoke.  Listen to how you feel and moderate your physical activities based on how you feel.  If possible, make your home a clean air space by running a  HEPA air cleaner in rooms you frequent.

Because smoke conditions can change rapidly and vary widely based on location, wind, fire flare ups and proximity to fires, the department encourages individuals to use visibility as a guideline to help gauge air quality at a given time and place and take appropriate precautions. 

For the most current information on particulate air pollution levels throughout the state, access Montana’s “Today’s Air” web site.  


August 19, 2018 11:00 AM

As of 11:00 a.m. on Sunday, air quality is Unhealthy in Frenchtown  and Seeley Lake and Unhealthy for Sensitive Groups in Missoula.

When air quality is Unhealthy, people with heart or lung disease, smokers, children and the elderly should limit heavy or prolonged exertion and limit time spent outdoors.  People with asthma should follow their asthma management plan. People experiencing symptoms of heart or lung disease associated with smoke exposure should contact their health care provider.

Conditions may improve tonight (or this afternoon) when another weather disturbance moves through western Montana.  However, there is likely to be haze and air quality impacts throughout the county today.  Currently, most of our smoke appears to be coming from the Washington fires.

Because smoke conditions can change rapidly and vary widely based on location, wind, fire flare ups and proximity to fires, the department encourages individuals to use visibility as a guideline to help gauge air quality at a given time and place and take appropriate precautions.  

For the most current information on particulate air pollution levels throughout the state, access Montana’s “Today’s Air” web site.

This morning’s satellite image shows thick smoke through most of Montana with a bit of clearing in Idaho.  The smoke has been drifting in a generally easterly direction this morning, so there is a chance that that patch of clearer air to the west of Missoula County in Idaho may reach us at some point today.  Source: CIRA and NOAA081918_AM colorLabeled 

August 17, 2018 8:00 AM

Last night’s smoke stuck around and we’re currently sitting at Unhealthy for Sensitive Groups conditions in Missoula and Frenchtown.  Air quality is Moderate in Seeley Lake.  When air quality is Unhealthy for Sensitive Groups, children, the elderly and people with heart and lung disease should avoid prolonged outdoor exertion.  

We may see some improvement after the inversion breaks later this morning, but our best shot for significant smoke clearing will be late this afternoon when a series of storms makes it way across the region.  The National Weather Service has toned down the surface-level wind forecast for our area, but there should still be significant atmospheric disturbance that will allow the lingering smoke to move out of our valleys.  If we get a break, it will likely be short-lived, so take advantage of the smoke break while it’s here – air out your house, run around outside, frolic in the daisies.  Really, let your imagination run wild.  The high elevation winds will continue to deliver smoke to our area over the weekend and into next week, so we’re likely to see a return to smoky skies by Saturday afternoon. 

Stay up-to-date on near real-time smoke data by visiting Montana’s Today’s Air website:   This morning the map is sporting a fall theme – all reds and oranges and yellows.  There isn’t a green dot on the map, which basically means everyone in Montana is dealing with smoke this morning.    Solidarity in suffering, amiright? 

There’s a good chance smoke season is going to get worse before it gets better.  If you haven’t taken steps to clean your indoor air, please check out the handouts (above) for handy tips about cleaning the air in your home.

August 16, 2018 7:00 PM

If you’re in Missoula and looking west, you may be wondering where Frenchtown went.  Or at least where the mountains in that general vicinity have gone.  It looks extra scummy that direction for two reasons: 1) we’re looking toward the sun and that always makes the smoke look extra bad (particulate matter scatters light like a champion), and 2) the air is pretty scummy in Frenchtown.  Conditions in Frenchtown have deteriorated to Unhealthy for Sensitive Groups, and the rest of Missoula County will likely reach Unhealthy for Sensitive Groups later this evening.  When air quality is Unhealthy for Sensitive Groups, children, the elderly and people with heart and lung disease should limit prolonged exposure. 

The smoke that’s been lingering overhead for days has finally mixed down to the valley floor and we’re seeing deteriorating conditions across western Montana.  The smoke may stick around overnight and into the morning hours, but by tomorrow afternoon we have a good chance of cleaner air.  The high pressure ridge that’s kept us under a constant haze will be replaced by an atmospheric disturbance heralded by strong winds and possible thunderstorms.  The winds should help scour smoke out of the valley floor and provide a window of breathable air.  The thunderstorms are likely to be mostly dry and, if lightning strikes in unfortunate locations, may result in new and exciting smoke in the general region. 

Our overhead smoke will continue to arrive from fires to our southwest tomorrow before switching to fires burning in Washington, Canada and northern Idaho and Montana for the weekend.  Fortunately, there aren’t any long-lived high pressure ridges in the forecast for the next several days, so we may get a break from the persistent haze.  (The persistent haze may be replaced by occasional smoke impacts as smoke drops down to say “hi” from time to time. There are a lot of fires burning in the region and the high elevation winds will keep delivering smoke to our area for the foreseeable future.) 

In today’s satellite photo you can see smoke blanketing the Missoula region under a bit of cloud cover.  The Canadian smoke blob has spun out and is currently hovering over Central and Eastern Montana and arcing over North Dakota and curving down into Nebraska.  Source: CIRA and NOAA

081618_PM color


August 14, 2018 5:30 PM 

I know it doesn’t look it, but we’ve been in Moderate air quality all day today.  The unrelenting haze has at times felt oppressive and it is certainly unappealing, but concentrations have remained steadily in the (upper) Moderate range.  Conditions in Missoula and Frenchtown have occasionally crept up near Unhealthy for Sensitive Groups, so some folks with heart or lung disease may very well be feeling the effects of the smoke.  Pay attention to how your body is responding to the smoke and take steps to protect yourself – reduce your exposure and spend time indoors in a location with filtered air.  If you have asthma, follow your asthma management plan.  The longer this drags on, the worse it is for everyone, and even Moderate smoke concentrations can start to wear you down. 

We’re likely to continue to see similar conditions over the next several days.  High pressure will keep us from clearing out until at least Friday, and upper level winds will be sending smoke our way from fires burning in Washington, Oregon and California.  The only “good” news I have for you is it looks like the smoke blob in Canada is likely to dodge Missoula County.  It’s currently rotating toward Montana, but as it moves south it’s more likely to land in Central and Eastern Montana than it is our region.  This is less good news if you’re in Central or Eastern Montana.  (There is a decent chance it’ll dodge Montana altogether, so don’t lose hope, Central and Eastern Montana!) 

We may see some smoke from Northwest Montana and the northern Montana/Idaho border creep down into our airspace this evening.  Also, there’s quite a bit of smoke lurking overhead, and there’s a chance some of it will mix down early this evening.  Be alert for changing conditions and check Montana’s Today’s Air website ( for near real-time air quality data. For the rest of the week, our smoke source is looking pretty decidedly to be fires burning in West Coast states. 

Smoke from fires burning throughout the region is creating hazy conditions in Missoula County.  Upper level winds in our area moving slowly, but they may deliver smoke from northern Montana fires into our valleys later tonight.  Source: CIRA and NOAA

081418_PM color

August 11, 2018 at 5 PM

As of 11 AM on Saturday Air Quality is Moderate in Missoula County.  With Saturday afternoon’s predicted cold front and increased winds, air quality should remain moderate through Sunday with some good air quality mixed in if the plumes of smoke stay above us or pass around the county.

Because smoke conditions can change rapidly and vary widely based on location, wind, fire flare ups and proximity to fires, the department encourages individuals to use visibility as a guideline to help gauge air quality at a given time and place and take appropriate precautions. 

For the most current information on particulate air pollution levels throughout the state, access Montana’s “Today’s Air” web site.  Thank You.  Also, I just want to say that those lemonade soft serve ice-cream drinks at the fair are delicious and I can’t believe it took me this many years to try one.  I figure that drinking one of those should help put out the fires.

In this morning’s satellite photo, you can see that the whole region is covered in smoke.  Distinct plumes should become more apparent later in the weekend as the winds increase. 081118_AM color Source: CIRA and NOAA. 

 August 10, 2018 at 5 PM

Air quality has been hovering around Unhealthy for Sensitive Groups for much of Missoula County today with Moderate air quality in Seeley Lake.  Expect better, but not smoke free, air quality this weekend once the cold front with winds appear.

Today's smoke appears to be coming from fires in Idaho and Oregon with other smoke mixed in from Washington and California.  With most of the fires at long distances from Missoula County, impacts from the smoke are much more moderate than last year when we had the ring of fire in Missoula County.  Let us hope our luck for no nearby fires continues for this year.

The high pressure ridge is going to break down as we head into Saturday and it will be replaced by a dry cold front that is accompanied by surface winds and much, much zippier transport winds coming at us from the southwest.  The smoke that’s stalled over our area will move off, but there’s a chance it will be replaced by California smoke this weekend.  Expect better, but not smoke free, air quality this weekend once the winds appear.  On the downside, the higher wind speeds will increase fire activity.


August 8, 2018

As of 10 AM on Wednesday, air quality is Unhealthy for Sensitive Groups in Seeley Lake and Moderate through the rest of Missoula County. 

When air quality is Unhealthy for Sensitive Groups, people with heart or lung disease, children and the elderly should limit prolonged outdoor exertion.  Anyone experiencing symptoms of heart or lung disease associated with smoke exposure should contact their health care provider.

Smoke and haze are expected to continue into Friday with a decent chance of smoke clearing a bit Saturday when a dry windy cold front moves through the region.  The bad news is that the winds will increase active fire behavior.

Because smoke conditions can change rapidly and vary widely based on location, wind, fire flare ups and proximity to fires, the department encourages individuals to use visibility as a guideline to help gauge air quality at a given time and place and take appropriate precautions. 

For the most current information on particulate air pollution levels throughout the state, access Montana’s “Today’s Air” web site.  Thank You


August 1, 2018 

No, you’re not imagining things. That really is wildfire smoke dimming the morning sun.  Wildfire smoke season 2018 is officially upon us!  Now, before you break out the balloons and streamers (or, alternatively, curl up into a little quivering ball – we don’t judge), you should know the smoke we’re seeing is from very far away and is still very high above us.  Fires in California and Oregon have been sending smoke our direction for the past several days, and while it’s been messing with our sunshine and mountain views, relatively little of it has hit the valley floor.  The air has looked worse than it is, and air quality has been generally Moderate (and frequently Good) in Missoula County all week.  

First, the bad news – based on mixing heights this afternoon, there’s a decent chance more of that smoke is going to come down to the valley floor.  If this happens, we may see air quality deteriorate to Unhealthy for Sensitive Groups.  Also, based on upper elevation wind patterns, we’re likely to continue to see smoke from Oregon and California headed our way into Thursday.

Now the good news – by Friday, the high pressure ridge will break down and the West Coast smoke will shift south of Montana.  A dry cold front it set to arrive Thursday afternoon, and the strong winds on Thursday and Friday should do a good job scouring the valleys clear of West Coast smoke remnants. 

Now the bad news again – dry cold fronts are pretty scary during fire season.  If we get lightning or have any fires start before the cold front gets here, we could end up with active fire behavior.  Fortunately, we do not currently have any significant nearby fires to be stirred up by the front, but it’s something to keep in mind. Be very careful while out and about – make sure you aren’t dragging any chains, do not flick cigarette butts out your vehicle window, and if you have a campfire, make sure it is dead out before you walk away from it.  I mean, stick you hand in that puppy. Roll it all around in the ash.  If you don’t want to do that with your dead campfire, it’s not dead enough. 

We’ve had a nice break from wildfire smoke (at least compared to last year), but technically the season is still young.  Be alert for changing conditions and bookmark Montana’s Today’s Air website so you can keep track of the smoke we’re seeing at our monitors:


July 20, 2018

This is the third of a short series of blogs about becoming a smoke-ready community.  Stay tuned this summer as we prepare for wildfire season and scroll down to catch up on previous posts!

Remember when I talked about MERV ratings a few weeks ago? Did that make you uncomfortable? Well, buckle up, friends. 

Today we’re focusing on creating clean indoor air in large spaces such as offices, schools, fitness centers, etc.  Creating our own individual happy clean rooms in our homes is all well and good, but most of us can’t spend wildfire season hiding out at home.  We’ve got jobs, yo.

But wait, you say, my office is air conditioned! That means we’re good to go, right?  Well, it depends.  A lot of HVAC systems are, to be kind, older than dirt.  They do their job delivering fresh air into your breathing space and modifying the air temperature, but that’s about it.  They were designed and installed back in the good old days, when outside air was always going to be better for you than the stale indoor air. (For any of ya’ll who remember Missoula winters in the 80s, you know this wasn’t necessarily true even decades ago.)

Now, before we get into this, here is my disclaimer: I am not an HVAC technician.  I’ve spoken with some folks who know things and I’ve done a lot of reading, but this does not make me an expert.  If you want to upgrade your building’s filtration (and I hope you do), talk to your HVAC technician.  This blog will hopefully give you some starting points for asking questions, but it may not give you the correct answer for your situation.

Who should be thinking about this?  Anyone who owns, works in, or goes to a school, office, indoor recreation area, fitness center, etc.  As I mentioned in a previous post, being inside during a wildfire smoke event does not mean you’re protected from the fine particulate matter in smoke.  Being inside with filtered air, does. 

The ClifsNotes for folks with no time: upgrade your HVAC system’s filter, reduce or close the fresh air intake when it’s smoky, and keep doors and windows closed. 

Ok.  It’s MERV time.

Last wildfire season was the first time I’d heard of MERV, so don’t feel bad if you’re sitting there asking, “What’s a MERV?”  MERV stands for Minimum Efficiency Reporting Value.  It was developed by the American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE) to evaluate air filters.  The MERV ratings classify a filter’s ability to capture different sizes and amounts of particles at each pass.  For example, a MERV 3 will effectively filter large particles, such as cat hair and the bits and pieces of insects that end up in HVAC systems.  No one wants to inhale bug parts, but these are not the particles we’re concerned about during wildfire season. With each pass, a low-rated MERV (1-4) will filter less than 20% of coarse particles that are 3-10 microns in diameter (like road dust) and won’t do anything to stop the fine particulate in smoke.  A MERV 13, meanwhile, will remove about 90% of all particles larger than 1 micron in diameter and will remove about 50% of fine particles 0.3-1 micron in diameter with each pass.  MERV 17-20 gets into HEPA range, with greater than 99.9% of all particles 0.3 microns and larger being removed with each pass.  High MERV ratings (15+) are typically found in hospital and surgery settings. If you’re craving more numbers and details, here’s a link to a handy dandy chart:

HVAC systems are designed to meet standards set forth by ASHRAE.  ASHRAE does good work, but they haven’t taken a serious look at wildfire smoke yet, and there are no ventilation design standards for buildings in wildfire-prone areas.  Currently, ASHRAE’s standard for indoor air filtration in commercial buildings is MERV 8 (which is better than the MERV 6 they recommended prior to 2016).  The standard for low-rise residential buildings is a MERV 6 on a recirculating airstream. Both the commercial and residential ASHRAE standards recommend a higher MERV in areas with elevated PM2.5 pollution, but there are no requirements or specific guidance.  There is an interesting article in the ASHRAE Journal that discusses MERV ratings appropriate for cities with chronic high PM2.5 pollution, but it doesn’t address the pollution patterns typical in wildfire-prone areas. (

Because ASHRAE only requires a MERV 8 in new commercial buildings, that’s what you’ll typically find. There are reasons for the hesitation to install more robust filters – a higher MERV filter will need to be changed more frequently and there are added concerns about air flow and energy demands.  A higher MERV-rated filter means more work, and potentially more cost, for facilities.

If we’re being honest, a MERV 8 is probably ok most of the year.  We saw MERV 8s put out a valiant effort last wildfire season.  They couldn’t filter out all the smoke, but buildings using a MERV 8 were in much better shape than those with less filtration. (Note that MERV 8 filters aren’t rated for filtering fine particulate.  However, they do provide some filtration benefit if the air recirculates multiple times through the filter.  If you aren’t recirculating your building’s air, a MERV 8 isn’t going to do a whole heck of a lot against wildfire smoke.) 

Many older HVAC systems will not have a high or even middle-of-the-road MERV-rated filter.

So, what to do?  Talk to your HVAC technician to find out the maximum MERV-rated filter your system can handle.  If you can upgrade your filter(s) for wildfire season, do so.  Don’t forget to stock up on extra filters – the higher-rated filters will catch more material and will need to be changed more frequently.  Use a prefilter to prolong the life of your higher-rated MERV filter.  If you want to take a serious stance against wildfire smoke, aim for a MERV 13 or better in your HVAC system.  To save on energy and filter costs, go back to a MERV 8 when the smoke is gone.

If you can limit the amount of outside air your system delivers during a smoke event, do so.  By reducing the amount of smoky air introduced to the building, your indoor air will stay cleaner.  Also, as your indoor air recirculates through your filter, it will continue to improve.  Some modern commercial HVAC systems can be designed with the proverbial “big red button” to shut down fresh air intake during pollution episodes.  If you do completely bypass your fresh air intake, be sure to monitor the indoor CO2 levels and bring in fresh air as needed to keep CO2 within a safe range.

(ASHRAE standards require a certain amount of fresh air delivery.  However, the organization has acknowledged that sometimes the outdoor air is not optimal.  Per, ASHRAE, “The Indoor Air Quality (IAQ) Procedure of ASHRAE Standard 62.1 allows lower ventilation rates if alternative methods are used to reduce exposures to contaminants of concern, including the use of filtration or air cleaning.” .)

In addition to upgrading your HVAC’s filter and reducing outdoor air intake, it is important to limit your building’s door and window use.  Try to restrict general coming-and-going to a single entrance and keep windows closed.  If you have a foyer or small entryway, consider placing an appropriately sized room air purifier with a true HEPA filter in that space to provide some extra air cleaning before passing the buck to your HVAC’s filter.

If you cannot upgrade your HVAC filter, it may be a good idea to invest in some room air purifiers with true HEPA filtration.  You should particularly consider going this route if there will be anyone with heart or lung disease, children, pregnant women or elderly persons using that space, or if people will be exercising in the space.  You may feel a bit like Sisyphus with your room air purifiers processing a new burst of smoky air every time your HVAC whirs to life, but some air cleaning is better than none.

Note that I didn’t get into unit ventilators.  These are the standalone units that you’ll find in a lot of older classrooms and some office buildings.  They bring fresh air inside on a room-by-room basis.  It *is* possible to get a MERV 13 for unit ventilators, but it’s a custom job.  Folks in buildings with unit ventilators should talk to their HVAC technicians to come up with good solutions for wildfire smoke.  Room air purifiers with HEPA filtration may be the simplest solution.

As always, Climate Smart Missoula has some great tips on keeping homes, offices and commercial spaces smoke free this wildfire season:  I've added some updated flyers from Climate Smart Missoula about selecting HEPA filters and preparing your central air system for wildfire smoke in the HANDOUTS section (above).

Remember how I’ve been hinting that I’d talk about the latest and greatest fire season outlook from the National Interagency Fire Center?  Well, spoiler alert, it’s going to by hot and dry this summer.  Shocking, right? We’re supposed to have an average July fire season and an above-average fire season in August and September.  Based on the last two weeks and the long-range forecast, I’d say that’s probably pretty accurate.  Things are drying out fast, and we have our first significant Montana fire burning down on the southern Montana/Idaho border. 

You can check out the full outlook here:

Note that Oregon and Central Washington were supposed to have an above-active July, and that seems to be the case.  There are multiple fires in Oregon right now, and there’s a decent chance smoke from the large grass fire in Central Washington will arrive in Montana this weekend.  (The nice thing about grass fires is they tend to be short-lived.  That’s probably the only nice thing about grass fires.) We may also see more Oregon smoke in the coming days. 

Until our own fires take off, I expect to continue to see intermittent haze and occasional smoke impacts from the out-of-state fires.  We’ll start sending out regular smoke updates when we get further into the season and see smoke impacts other than haze and moderate air quality.


July 5, 2018

This is the second of a short series of blogs about becoming a smoke-ready community.  Stay tuned this summer as we prepare for wildfire season and scroll down to catch up on last week's post!

Did you go outside today?  It’s hot.  It’s going to be hot again tomorrow.  And, depending on which long-range forecasters you’re tuned in to, it’s going to be hot for the rest of the summer.  You know what that means!  It’s time to talk about air conditioning!  And smoke!  There’s always a way to work smoke into a conversation.  This is why air quality specialists make terrific (or terrible) dinner guests. 

Anyway, with the potential for another hot and smoky summer, it’s important to make plans for keeping your house cool.  According to the Centers for Disease Control, every year more than 600 people in the United States are killed by extreme heat.  However, heat-related illnesses are preventable, and one of the steps you can take is cooling your home. 

Do you have central air conditioning? Awesome!  If possible, bypass the fresh air intake when smoke arrives, upgrade your system’s filter (see last week’s blog post), keep your doors and windows closed, and enjoy the cool, clean air.  Also, maybe invite some friends or relatives over to share in your bounty. 

A lot of us do not have central air conditioning.  That leaves us with window air conditioners, portable air conditioners (those rolling things with giant hoses that send exhaust out the window), and the good old-fashioned method of opening windows at night and using fans to push hot air out and draw cool air in. Whichever method you use is personal preference, but the tricky thing here is smoke infiltration.  Opening windows at night works pretty well when it’s not smoky.  Unfortunately, the nice cool air that is so refreshing at night is the same cool air that traps smoke near the valley floor.  It’s not uncommon for us to see thick overnight smoke, and that smoke will move right into your home when you open your windows.  If you have no other option, it may be best to open your windows for long enough to cool your home, and then, once you’ve closed the windows, crank up your air purifier(s) to remove the smoke.  It is very important to avoid heat stress.  It can feel like a lousy bargain – clean air or cool air, but if you have an appropriately sized air purifier with HEPA filtration on hand, you should be able to clean the smoke out of a room relatively quickly. 

And now, a brief foray into window and portable air conditioners.  First, we need to talk very briefly about how air conditioners work.  Disclosure: I am not an air conditioning expert.  I don’t even play one on T.V.  I have, however, honed my googling skills.  After much trial and very little error, I recommend the search queries “How do window air conditioners work?” and “How do portable air conditioners work?” Don’t let anyone tell you we aren’t a full-service health department.


Air conditioners transfer heat from your inside air to the outside air in a process that involves a cool air cycle and a hot air cycle. In the cool air cycle, the air conditioner draws indoor air across cooling coils, transferring the heat from the air to the refrigerant in the coils.  The now-cooled air is released back into the room.  The heated refrigerant needs to be cooled down, so in a separate part of the machine, the air conditioner pulls outside air across the heated refrigerant.  The heat from the refrigerant transfers to the air and the machine sends the now extra-warm air back outside.  A properly installed window air conditioner should keep theses two air cycles separate.  Inside air cycles across the cooling coils and is released back inside and outside air cycles across the heated refrigerant and is released back outside.

 Here’s a nifty link to a site that describes the process in better detail:

 Here’s a snazzy diagram for those of us who like our air conditioner explanations in picture form: 

Because window ACs recirculate room air, they generally keep indoor air in and outside air out.  However, some models have a feature that allows the user to bring in fresh air.  Check your model for a fresh air intake and be certain to close it during a smoke event.  Also, you will want to make sure the area around your window AC is as sealed as possible to limit smoke infiltration around the sides of the machine.  If you have a jerry-rigged setup such as a window AC unit in a side-sliding window, you may need to basically treat your window AC unit as an open window.

If you want to use your window air conditioner to help filter your indoor air, research your machine’s ability to function with an upgraded air filter.  Window air conditioners have filters, but they’re designed for catching dust and pet hair, not the fine particulate in smoke.  There are some aftermarket window air conditioner filters out there, but they can be a bit dodgy on specifics about particulate removal.  Also, you need to cautious about adding an upgraded filter to a window air conditioner because the increased resistance can put significant stress on the machine. If you choose to upgrade your filter, get the highest MERV-rated filter you can for your model of window air conditioner, and use your room air purifier with HEPA filtration to clean whatever is left over.

Because of their design, portable air conditioners can be used with more window types than a window air conditioner, so they may be an option worth considering if you have side-sliding windows.  However, they tend to be considerably more expensive than window air conditioners and not all portable air conditioners are created equal.  Portable air conditioners come in two types: single and dual hosed.  In both types, the hoses bring in outdoor air to cool the refrigerant and send heated exhaust out the window. A single-hosed portable unit will use the same hose for both intake and outtake.  Because it can’t draw in enough outdoor air to cool its refrigerant, the single-hosed unit will also draw in your nice cool room air to cool itself down and send that air out the window.  This could be problematic during fire season, because the process creates negative pressure in your home.  The negative pressure will pull outside air into your house through various nooks and crannies, and if it’s smoky outside, it may also pull smoke into your home.  Dual-hosed portable ACs avoid the negative pressure issue by having a hose dedicated to drawing outside air into the machine to cool the coils.  This way, only outside air is exhausted out the window – inside air stays inside and the pressure in your house should remain stable.  However, dual-hosed portable air conditioners tend to be quite a bit more expensive than single-hosed machines.  If you are using a portable air conditioner, try to seal the edges where the exhaust plate meets your window as much as you can.  Otherwise, there’s a good chance smoke will sneak in around the edges.   Use your room air purifier to clean out whatever smoke ends up inside.  This will be particularly important if you have a single-hosed portable AC. 

The take home message is this: You need to be able to cool your home, and there’s a good chance the process of cooling your home will introduce smoke into your breathing space.  If you have an air purifier with true HEPA filtration you can reduce the amount of smoke that stays in your home.  Last summer, Climate Smart Missoula ran particulate sensors in a house that did not have air conditioning but did have room air purifiers with HEPA filtration.  Yes, smoke came into the house overnight when smoke rolled into town.  However, within a couple hours of closing the windows and turning on the air purifiers, that house had some of the best air in Missoula. 

If you don’t have air conditioning and, based on your health, you can’t allow any smoke into your home, your best option may be to find somewhere else to be next time smoke rolls into town.  You may need to stay somewhere local with air conditioning and filtered air or leave the valley to find clean air. 

I would be remiss in my air specialist duties if I didn’t remind ya’ll that air conditioners can be energy hogs, which is a no-no when we’re trying to confront climate change by reducing energy use.  However, your health is crazy important, so I’m not going to tell you not to use it.  Do try to limit your air conditioner use to the amount needed to keep your house at a safe temperature and as smoke-free as possible.  Climate Smart Missoula has some nifty tips for keeping your home cool(ish) in the summer:



JUNE 27, 2018

This is the first of a short series of blogs about becoming a smoke-ready community.  Stay tuned this summer as we prepare for wildfire season!

It’s officially summer.  The days are long, the grass is green(ish), and it’s time to get outside, enjoy the fresh air and make plans for the rest of your summer!  And by make plans, I mean assess your indoor air filtration and take steps now to protect yourself later this summer when wildfire smoke rolls back into town.  You didn’t really think this was going to be uplifting, did you?

The wildfire outlook is grim – long range forecasters at National Predictive Services are expecting a hot and dry summer in the Northern Rockies with above average fire activity.  Even if we get super lucky this year and the lightning doesn’t fall in our neck of the woods, it’s going to fall somewhere, and there’s just a darn good chance that we’re going to see smoke this summer. 

It shouldn’t come as a surprise to you that smoke is bad news.  Wildfire smoke contains fine particulate matter and a vast array of volatile organic chemicals (VOCs) such as benzene, acrolein and formaldehyde.  The particulate matter is our primary health concern, but the VOCs can still make you pretty miserable.  VOCs from wildfire smoke can cause headaches, stinging eyes, upset stomach and a scratchy throat.  Meanwhile, the particulate matter can cause respiratory and cardiac issues such as reduced lung function, exacerbated asthma and increased risk of heart attack and stroke.  The fine particulate matter in smoke (typically less than 1 micron in diameter) is so tiny that it evades all your natural defenses when you breathe it in.  Once it enters your lungs, the fine particles can pass into your bloodstream and set off an inflammatory response.  It’s nasty stuff. And, if you don’t take steps to clean your indoor air and keep smoke out, next time smoke rolls into the valley it’s also going to roll into your home.

The 2017 wildfire season was brutal, but it led to an important paradigm shift in how we approach wildfire smoke.  It’s time to stop reacting to smoke by hunkering down and waiting for it to go away.  As any of us who lived through the 2017 wildfires know, sometimes the wait for the smoke to leave can take weeks, if not months. (No one wants to hunker for that long, it’s got to be terrible for your back.)  It’s time to be proactive.  There is a lot of important work being done around Missoula County to become a fire-ready community.  It’s time to also become a smoke-ready community.

So, what can you do?  A lot, actually.

Start by assessing your current cooling and air ventilation status.  Do you have central air?  If so, you may be able to achieve some indoor air quality improvements by upgrading the filter on your HVAC system.  No central air? Consider investing in a room air purifier with HEPA filtration. 

Next, make a plan about protecting your cleaner indoor air space.  If you have central air, run it on a recirculate mode (if possible) to avoid bringing in outdoor smoky air.   Even if you don’t have air conditioning, you can likely run the fan with the heat off and push air through your home (and hopefully through a good filter).  If you have a room air purifier with HEPA filtration, set it up wherever you’re spending most of your time (first make sure it’s appropriately sized for the room that it’s in). The more times air passes through your filter, the better.  Avoid opening windows or doors during a smoke event.  Good door and window control can do a lot to limit smoke infiltration.

Last summer, Climate Smart Missoula had particulate sensors running in multiple indoor locations around town.  The data from those sensors were both fascinating and, largely, depressing.  Locations without any filtration in place showed particulate concentrations that almost mirrored outdoor conditions.  However, the sensors did show indoor air quality improvements in buildings with recirculated air and moderate filtration (MERV 8), and we saw rapid and impressive indoor air quality improvement in a house running room air purifiers with HEPA filtration.

The main takeaway from last summer’s indoor air quality screening was this: If you do not take steps to filter your indoor air during a wildfire smoke event and you don’t limit window and door use, you might as well be outside.  Being inside does not protect you from smoke.  Being inside with filtered air, does.

That was the CliffsNotes version.  If you want to get into the weeds, read on:

Room air purifiers with HEPA filtration

Room air purifiers with HEPA filtration can dramatically improve indoor air quality.  These standalone units use a fan to pull air through a true HEPA filter, which mechanically removes the fine particles in smoke.  There are a lot of options on the market, and they all do pretty much the same thing with various bells and whistles. 

If you choose to get a room air purifier, plan on keeping it in the room where you spend the most time.  For example, it’s a good idea to, at a minimum, run an air purifier in your bedroom while you sleep.  Also, try to keep windows and doors to the room with the air purifier closed to allow the machine to recirculate the air through its filter.

Important questions to ask when you look at an air purifier:

  1. Does this unit use a true HEPA filter?

    There are “HEPA-like” filters on the market, which are not the same thing as true HEPA and won’t be as effective at removing the fine particulate in smoke.

  2. How many square feet will it cover?

    If you end up with an undersized air purifier that is unable to recirculate the room’s air through its filter 2-3 times per hour you likely won’t see significant indoor air quality improvements

  3. Does this unit produce ozone?

Some air purifiers produce ozone, which is a criteria pollutant and harmful to human health.  Check to make sure the unit you are interested in has been approved by the California Air Resources Board (CARB) here:  The CARB only approves units that do not produce harmful levels of ozone.

Good questions to ask:

  1. Is this unit Energy Star rated?
  2. Is it noisy?

Valuable question to ask:

  1. How effective is the unit at removing VOCs?

There are multiple methods for removing VOCs, but the most common one you’ll see is an activated carbon prefilter.  While activated carbon can remove VOCs, be aware that it can get saturated pretty quickly, which limits the effectiveness of a lot of the carbon prefilters on the market.  If you are concerned about the VOCs in smoke, you can plan on changing the prefilter out frequently or you can invest in an air purifier with a robust activated carbon filter.  Note that the hefty activated carbon filters can be quite pricey.  Typically, the more fancy the VOC removal, the more expensive the machine (and the replacement filters).  For some folks, though, removing VOCs will be worth the price.


Central Heating and Air Systems

If you have central air, you may be able to improve your indoor air quality by upgrading your system’s air filter.  Air filters are rated using the Minimum Efficiency Reporting Value (MERV), with ratings ranging from 1-20.  The higher the MERV rating, the more effective the filter will be at removing small particles.  The minimum MERV rating that has a promise of removing the fine particulate in smoke is MERV 13. You don’t reach HEPA levels of particulate removal until MERV 17.  However, a MERV 13 has shown to be effective at removing the fine particulate in smoke when the system is set to recirculate air through the filter.  The more times air passes through the MERV 13, the cleaner it becomes.  Note that as the MERV ratings increase, the cost of the filters also increase.  Also, a higher MERV-rated filter will likely need to be changed more frequently due to the amount of material it accumulates.

Now, a word of caution – not all systems will be able to handle the added airflow resistance associated with higher MERV ratings.  You may want to have an HVAC technician check your system before upgrading your filter.


We’ve continued working with Climate Smart Missoula as we prepare for this wildfire season.  Climate Smart has been working to update their wildfire smoke pages, and they have all kinds of useful info for you.

HEPA room air purifier info and recommendations:

Wildfire smoke health concerns and recommendations:

The California Air Resources Board has done a lot of work assessing clean indoor air strategies and they take a lot of the guesswork out of the process.

Air Cleaning Devices for the Home (FAQs) has a lot of great information about creating clean indoor air spaces.  Note that they call room air purifiers “portable air cleaners.” 

California Certified Air Cleaning Devices.  Looking at purchasing a room air purifier?  Make sure it’s on this list! 

Do you have a lot of free time and want to read up on indoor air quality research?  CARB has you covered!

MERV rating chart


EPA Guide to Air Cleaners in the Home (2008)



Air Quality: Discussion

Wildfire smoke air quality updates will be back Summer 2018!

This web page is not updated on weekends or holidays unless air quality becomes Unhealthy for Sensitive Groups or worse. Call the air quality hotline at 258-3600 on weekends to get the most current air quality update.

If you operate a woodstove, fireplace or other solid-fuel burning device, you will want to get in the habit of checking this web page or the Air Quality hotline (258-3600) for up-to-date changes in Missoula's air quality. Woodstoves, fireplaces and other solid-fuel burning devices are restricted during alerts and warnings.


Air Pollution Alerts and Warnings

Missoula Air Stagnation Zone - Stage I Alert Stove Restrictions

Impact Zone M - Stage II Warning Stove Restrictions

Montana PM2.5 Today's Air Monitoring Network

Wildfire Air Quality Health Categories

Woodstove Operation Tips for Clean Burning