Tracking Air Quality in a Wildfire-Filled World

Originally published at: Tracking Air Quality in a Wildfire-Filled World - TidBITS

Stressed out by unhealthy air quality levels caused by smoke drifting south from wildfires in Canada, Adam Engst explores resources that report outdoor and indoor air quality to inform decisions about how to react.


Thanks very much Adam, by far the best analysis I’ve found. I’ll be monitoring PurpleAir for my walking and cycling routes (Belmont and Concord, MA). The last couple of days have been nasty here, but nowhere near as bad as Ithaca, it seems.

[edit] Good luck with that MCL!


Maybe six or seven years ago there was a wildfire about 30 miles from us that dropped a lot of ash in the park where I did my exercise walking. I usually wore a dust mask for facial sun protection under my hat. That time the smoke smelled strong even with the mask on.

I tried two layers of mask and then I could not smell the smoke. That is now my approach both to smoke and COVID exposure, although I now usually use an N95 mask over a dust mask.

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You mentioned the iPhone Paku app for the PurpleAir data. I only came across this yesterday for the first time but what I tried was the app running on my M1 Mac mini.

Perhaps unsurprisingly, other countries have their own scales, so air quality can be difficult to compare with far-flung friends and family.

The PurpleAir sensors are fairly widespread and you may well find coverage in distant lands that concern you. (It looks like much of western Europe has a fair bit of PurpleAir coverage, so getting familiar readings may not be quite so bad as you initially thought.) I’m in Scotland (turns out there’s a PurpleAir sensor about 4 miles away from me in Glasgow’s city centre) and first heard about the seriousness of this problem a few days ago when I was talking to elderly relatives in Sarnia - on the Canadian side of the border at the south of Lake Huron.

The problem with the Paku app (at least with the desktop version) is that there doesn’t appear to be any search facility. If you don’t simply want your own location, you have to drag the map to find it. While you can mark a sensor as a favourite, there’s no bookmarking facility, so navigating between Glasgow and Sarnia is a rather tedious process.

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Here is another site that provides the HRRR smoke data.

While the HRRR is a US-based domain, the RAP model covers all of North America.

I use both and they are very useful for looking at smoke forecasts at various heights above the ground as well as vertically integrated values.

Minor correction to the article: the HRRR Smoke has been an operational model – not experimental – since 2021.


Thank you for the article.

Here in western WA we now have a “wildfire smoke season” each summer, and sometimes in the spring or fall.

If you have no other filtration system, one of the recommendations for indoor filters is to bungie cord a MERV 13 filter to a box fan. It’s not fancy nor quiet, but if it is better than nothing.

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For people in WA state, the Washington Smoke Information blog is helpful and they have an RSS feed:

Washington Smoke Information

I have an old unsealed house, and I mostly like that because it improves ventilation. But it makes dealing with smoke much more challenging. After one of the first big smoke episodes I got some inexpensive HEPA room filters (Veva) that claimed they could handle ~200 sqft each, and a Winix C545 (360 sqft) from costco on sale. I also got the Temtop M10 based on Wirecutter (mine compares well with nearby purples). When the next big smoke came (AQ in 250-300 range) in a 100 sqft room, the Vevas made an inadequate difference even when set to high, but the Winix worked very well; I had to run it on high for awhile, but about medium kept up from there. Bought a second winix for the bedroom, and given the forecasts for this summer I wish I’d gotten one or two more when they were on sale again a few months ago.

Masks/respirators: PM2.5 has no odor, so you can’t go by smell. The smells are formaldehyde, benzene and other organic gasses that aren’t stopped at all by particle masks/respirators/HEPA filters (and not all gasses that are harmful have an odor). The farther smoke travels the less healthy it is, because the organics react with UV and produce more toxic compounds. These aren’t really tracked by current AQ measures, and aren’t even well studied yet, so probably assume things are worse than you think.

For viruses, use a good N95 respirator with no exhaust vent, and don’t stack them. If you think you need to stack, put the N95 on first or it won’t do any good–it needs a good seal to your face. I like the 3M Auras because they fit me well and are comfortable, but YMMV.

For smoke, if you aren’t around other people so viruses aren’t an issue, use a mask/respirator with a vent. They stay a little cooler and don’t get damp as quickly. But for all day use, a cartridge/filter respirator may be more comfortable and effective once you adjust it properly (along with a bonus halloween mask feature!) All are vented, so they aren’t helpful to avoid spreading viruses. I use P100 filters with ‘nuisance’ organic vapor protection, which does better than N95 on the particles, and by specification at least a fairly good job on combustion gasses. The gasses are blocked by an activated carbon layer at a minimum (disposable masks, filters) and may contain metals and/or salts to increase blocking of specific gasses (usually in cartages which is why they’re expensive.) The nuisance gas filters aren’t up to occupational exposure levels so you may want to also get a set of the fancier cartridges if you live in or downwind from a potentially very high smoke region. The below P100 filters are larger diameter than some, so they’re easier to breath through and they also last somewhat longer. (P = resistant to oil based particles, R = somewhat resistant, N = no oil resistance.)

I have these and have used them somewhat:

3M Medium Half Facepiece Reusable Respirator 7502/37082(AAD), Respiratory Protection, Medium

3M Advanced Particulate Filter 2297, P100 Respiratory Protection, with Nuisance Level Organic Vapor Relief

I don’t have these (yet?) but they may be of interest, especially the disposables:

3M™ Organic Vapor Cartridge/Filter 60921 (cartridge)

3M™ Particulate Respirator 8577, P95, with Nuisance Level Organic Vapor Relief (disposable)

3M™ Particulate Respirator 8247, R95, with Nuisance Level Organic Vapor Relief (disposable)

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A few additional thoughts about N95 masks, based on my personal experiences with multiple brands and styles of masks:

  • Masks with two straps make a better seal to your face than ear loop masks.
  • In addition to 3M, Demetech is a good source for NIOSH certified N95 masks. Demetech has sales on its masks, often 30% or more off, a few times a year.
  • It is common, as discussed above, to smell odors through N95 masks. I still wear a mask when I run errands; I always smell things like restaurant kitchens and people smoking various substances around my city.

Excellent info on the air quality and metering discrepancies. And reminding me to get replacements (now widely available post-Covid) of my 3M filters for when I paint/woodwork.
But growing up, I always remember the hazy summers… and the warnings about ozone depletion, smog and pollution. I think in the last 15 years, the air has been improved (EPA regulation do work), the increased EV cars on the road, and the move away from coal (who remembers acid rain?). Even now, my SUV cabin filters do a good job, and if I open the windows, I can smell someone smoking (still!) 4-5 cars ahead of me.
Rant- it’s a shame that where I live, 3 miles from Princeton, that there are neighbors that ignore the laws, and burn trash/cardboard and palletwood. There are open-fire bans and laws against this and yet you can’t pick your neighbors, they say. (We’ve call the local 911 (FD chief said to) to report and the neighbors retaliated with calling the police on a spotlight…cops here aren’t that “bright” as they never came back at night to see the issue is the streetlight not our spotlight. My advice, don’t move to NJ or if here, move out once your kids are done with highschool!)

Just want to add that the air quality tracking iPhone apps I use are Apple Weather, AirVisual, and AirNow. I began using the apps a few years ago during U.S. West Coast wildfire season and when travelling to places with high air pollution in Asia and Eastern Europe. The three are useful when used together, as mentioned in Adam’s original article.

On the recommendation of one Mr @rmogull, I started using 3M masks—I believe the Aura 9205+ is the exact model available to the general public. It’s a nice snug fit; it has some initial smell which turns some folks off, but dissipates quickly and hasn’t bothered me. It doesn’t fog my glosses where the KN94s my family prefers for comfort and fit do.

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Thanks for this! It is very comprehensive. I’ve been watching air quality since the pandemic, and it was interesting to see how air cleared up when people were ordered to stay home. My friend Karen wrote an app called Local Haze, which uses open source monitoring for local air pollution, so you can see which parts of your city may have higher AQI numbers and so you can keep an eye out for extremes due to smoke and pollution. I think it’s pretty useful. ‎Local Haze on the App Store

Pretty sure the notion that the wildfires are being caused by climate change is nothing but government propaganda attempting to perpetuate the climate change hoax. Here’s an article from Forbes giving a more realistic explanation: Wildfires Caused By Bad Environmental Policy Are Causing California Forests To Be Net CO2 Emitters

An inexpensive product for measuring your own air quality is the IKEA Vindstykra sensor. It measures PM2.5, temp, humidity, and also indicates if levels of tVOCs are increasing or decreasing.

It’s USB powered, but has no internal battery. It’s $50CAD

During the most recent ‘smoke event’ here in Ottawa Canada, it measured PM2.5 at 383 in my backyard. We have a high-efficiency Aprilaire 413 media filter (MERV13) on our forced-air furnace, and I’ve found it does an excellent job at capturing PM2.5 particles. If the furnace fan is running, interior AQ is typically well under 10. I now use the IKEA sensor to guide whether to run the fan 7/24, or on its intermittent ‘circulate’ setting.

Ah, the old “only one thing can ever happen at a time” fallacy. To greatly oversimplify: poor forest management has increased the fuel available and the warming climate has increased the amount and intensity of ‘fire weather’, the hot temperatures and low humidity that make it easier for a fire to ignite the fuel from a spark or lighting, and make it harder to control once lit. The more extreme fire weather also makes the fires grow faster and hotter than in the past.


Pretty sure that environmental policy in California (CA) does not impact wildfires in Canada (CA).

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No one has mentioned the BlueSky Canada interactive smoke map, which I have found to be very useful (assuming the data is accurate). You can find the map at

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If the forest management mindset used in Canada was the same as that used in California, then the results are similar.

Glenn, where do you buy them? Are they available locally or do you have to order online?

Thanks Adam for your interest into personal air quality apps. These are important for people with asthma and pulmonary issues. Here in Australia, our frequent bushfires are also being enlivened by climate change. The increasing intensity of these fires have reduced the noise of local climate change deniers.

Wildfire/bushfire monitoring apps now exist, and climate change monitoring and carbon tracking apps also exist. But I have yet to find any apps that link the two; maybe too difficult.