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How bad are smoke particles?

What’s in the air, how small it is, and what your filter can capture.

Understand your filter
A closer look at airborne particlesµm = micrometer · 1,000 µm = 1 millimeter
Particle size comparison on a logarithmic scale Each major step is ten times larger. Wildfire smoke often includes particles around 0.4 to 0.7 micrometers, within fine PM2.5. Fine combustion particles are 2.5 micrometers or smaller. Coarse dust spans 2.5 to 10 micrometers. Most mold spores are about 2 to 10 micrometers. Intact pollen is about 10 to 100 micrometers. Hair, shown only for scale, is around 50 to 70 micrometers. These are approximate illustrative ranges, not complete distributions. The filter comparison follows below. 0.1 µm1 µm10 µm100 µm0.32.5 Wildfire smokeCommon fine-particle range* ~0.4–0.7 µm Fine particles · PM2.5Combustion, soot & mixtures ≤ 2.5 µm; includes particles below this axis Coarse particlesDust & biological fragments 2.5–10 µm Mold sporesAllergens; some species produce toxins ~2–10 µm; fragments can be smaller Intact pollenAllergenic proteins, not a generic toxin ~10–100 µm A human hairDiameter, for comparison only ~50–70 µm LOGARITHMIC SCALE · Each major step is 10× larger. Bar thickness is decorative.

*Approximate particle diameters; aerosol categories commonly use aerodynamic diameter. Smoke contains a wider distribution, including ultrafine particles. Categories overlap: wildfire smoke is part of PM2.5, and pollen or mold fragments can be much smaller than intact grains or spores. Larger particles are usually easier to filter; finer fragments need finer-particle capture. Pollen size research · Mold spore sizes · Mold toxins.

Smoke & combustion

Particles can carry organic compounds, including PAHs, and metals. The mixture depends on what burns; not every particle contains every toxin.

Dust & biological material

Dust may carry allergens, microbes or metals such as lead, depending on its source. Pollen and mold contain allergens; particle size alone cannot identify toxicity.

Gases are a different problem

Smoke also contains gases such as carbon monoxide and VOCs, including benzene and formaldehyde. They are not particles on this chart.

Match the filter to the particle

Minimum average capture in the tested size band, per air pass. These are filter test ratings—not a promise of room-wide removal.

Particle capture by filter rating
Filter media0.3–1 µm
Fine smoke particles		1–3 µm3–10 µmWhat to know
MERV 8Not specified≥20%≥70%Coarser filtration; not the preferred smoke upgrade.
MERV 11≥20%≥65%≥85%Some fine-particle capture.
MERV 13≥50%≥85%≥90%A smoke-filtration starting point if your system supports it.
MERV 16≥95%≥95%≥95%Requires a system designed for its airflow resistance.
HEPA≥99.97% at 0.3 µm; smaller and larger particles are captured too.A separate standard, commonly used in portable cleaners. Check smoke CADR as well.
For gases and odors: particle filters are not enough.

Activated carbon or other sorbents can reduce some gases, depending on media amount and chemistry. Neither MERV nor HEPA is a gas-removal rating. Ordinary home air cleaners do not reliably remove carbon monoxide; use CO alarms and follow emergency guidance.

Sources: AirNow smoke guide · EPA MERV ratings · EPA HEPA definition · Indoor particle sources. Reviewed October 19, 2026.

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