Canadian Wildfire Smoke Is Back. What Does That Mean for Your Building?

Jul 15, 2026

Smoke from the Canadian wildfires is once again affecting air quality across much of the Northeast. Most people are paying attention to outdoor air quality alerts, but what often gets overlooked is what is happening inside buildings.

Wildfire smoke is made up of very small particles, many measuring 2.5 microns or smaller. These particles can make their way indoors, even in buildings with well-maintained HVAC systems. If your filters are not capturing those fine particles effectively, indoor particle levels can rise quickly.

We have seen this happen before.

During previous wildfire smoke events, Aircuity customers watched their dashboards as indoor particle levels climbed throughout the day. On one particularly smoky day, more than 30 customer sites recorded indoor particle levels that were so much higher than normal that Aircuity’s analytics flagged them as “failed high” and generated alerts that looked like sensor issues. There were no sensor problems. The system was simply detecting the impact that extremely poor outdoor air quality was having on the air inside those buildings.

(data from customer site downwind of wildfires showing spike in indoor particles during a past year’s event)

That is why measuring particles is so important.

If your building has an Aircuity outdoor air particle sensor, you can compare outdoor and indoor particle levels to see how well your filtration system is performing. If you do not have an outdoor sensor, free resources like AirNow or PurpleAir can provide outdoor particle data that you can compare with your Aircuity measurements.

Looking at both sets of data lets you calculate your filtration effectiveness instead of assuming your filters are doing their job.

Smoke particles are especially difficult to capture because they are so small.

A typical MERV 8 filter captures less than 20 percent of particles between 0.3 and 1 micron. It captures about 20 to 50 percent of particles between 1 and 3 microns.

A MERV 13 filter performs much better. It captures about 50 percent or more of particles between 0.3 and 1 micron and more than 85 percent of particles between 1 and 3 microns. That is why MERV 13 or higher is often recommended during wildfire smoke events.

The data can help answer important questions.

Are your filters due for replacement?
Would upgrading to MERV 13 improve indoor air quality?
Are there low pressure drop filters that can improve particle removal without a large energy penalty?
Should outdoor air intake be reduced while smoke levels are high, when building operations allow?

The answers will be different for every building. Having real time data makes it possible to make decisions based on what is actually happening and create a healthier indoor environment instead of relying on assumptions.

As wildfire smoke becomes more frequent, understanding what is happening inside your building is just as important as tracking outdoor air quality. Aircuity gives facility teams the information they need to understand filtration performance, respond to changing conditions, and make informed decisions.

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