Snow depth and winter IAQ

Snow affects outdoor air quality in two opposing ways. Falling snow scavenges particles from the air much as rain does (see precipitation and air quality), and a review of snow-scavenging research concludes that, for the same amount of water, it is probably more effective than rain, though estimates vary by more than tenfold. After a snowfall, the air is often clearer than before.

Persistent snow cover does the opposite. A snow-covered surface reflects 80 to 90% of solar radiation (high albedo); the air immediately above stays cold while air higher up warms; the resulting temperature inversion traps emissions near the ground. NOAA documents the meteorology. Cities in mountain basins (Salt Lake City, Calgary, Denver) experience some of their worst PM_2.5 exposure during multi-day winter inversions over snow.

For households with wood-burning, this is the canonical "wood smoke trapped in the valley" pattern. The combination of snow-covered ground, clear cold nights, and active wood stoves can produce outdoor PM_2.5 levels in the 100s of µg/m³ in moderate-sized cities. See wood stoves and fireplaces. Terrestream does not predict inversions, so on cold, calm winter nights check your local air-quality forecast.

Indoor implications: snow depth correlates with reduced infiltration (envelope sealing is more effective when outdoor wind is calm under inversion conditions), so indoor pollutants from internal sources persist longer when snow is on the ground. Terrestream uses the same bands in winter as in any other season. It checks outdoor air quality before it suggests opening windows, so it will not suggest airing out while outdoor fine particles are elevated.