Wildfire Smoke: What Hydroxyls Can Do
What’s actually in the smoke
Often we focus on the particles in smoke, because particles are what you can see and what monitors measure. But they aren't all that matters.
In the FIREX-AQ study, researchers sampled smoke from four fires across Idaho and Washington and measured the gases. Benzene ranged from 0.04 to 25 parts per billion. Modelling chronic exposure, they projected one to nineteen extra cancers per million people. Toluene, ethylbenzene, xylenes and hexane were also measured alongside it.
This isn’t a problem which only affects where the fires occur, either. Smoke influence was detected at background monitoring sites outside the fire zone, with benzene still elevated to 0.5 ppbv. NOAA ranks biomass burning — wildfires included — as the second-largest source of VOC pollution overall.
It gets in, and then it stays
This is the part that surprises people.
Researchers injected smoke into an instrumented house and watched what happened. The VOCs didn’t leave when the smoke did. They moved into the walls, carpets, upholstery and soft furnishings — and once the air cleared, those surfaces reversed direction and became emission sources, feeding the compounds back into the room for days.
Opening windows helped less than you’d expect; the authors found ventilation played “a minor role,” because what governs the process is how the compounds partition into surfaces rather than how much air you move.
In homes affected by the Marshall Fire, VOCs were still measurable weeks later — longer than the researchers expected, by mechanisms not yet fully understood.
It’s why a house can smell of smoke long after the smoke is gone, and why the smell returns on a warm day.
Why a filter can’t reach it
The compounds are in the surfaces, not just the air. A filter can only treat air that passes through it, so it never reaches them. That is not a flaw in filters — it is the boundary of what a filter is.
Hydroxyls work differently. They move through the room and react where the compounds actually are — in the air, and on the surfaces holding them.
Hydroxyl radicals are the atmosphere’s own route for breaking organic gases apart: the radical takes a hydrogen atom, the molecule comes apart, and the chain ends in carbon dioxide and water vapor. It is the dominant removal pathway for most VOCs outdoors, and direct measurements have found the same chemistry running indoors at concentrations comparable to outdoor urban air.
What we know, and what we’re still testing
Where WellisAir fits
WellisAir is one layer, not the whole answer.
The EPA sets out three strategies for indoor air quality, in order: remove the source, improve ventilation, then clean the air. For smoke that order is worth following:
- Keep it out while the air is bad. Close windows and doors during a smoke event, and run recirculation rather than drawing outside air in.
- Clean the surfaces afterwards. Vacuuming, mopping and dusting physically remove the reservoirs holding smoke compounds. This is the step most people skip, and the research says it matters.
- Then treat what’s left. That is our layer — the compounds still in the air and still coming back out of the surfaces, after the sky has cleared and the cleaning is done.