Indoor Air Pollution Is a Bigger Problem Than Most People Realize

[ajie]

We talk a lot about outdoor air quality — factory emissions, traffic exhaust, wildfire smoke. But the air inside our homes is where we actually spend most of our time, and in many cases it's significantly more polluted than the air outside.

The numbers from the WHO's 2021 Global Air Quality Guidelines are stark. Air pollution causes more than 7 million deaths globally every year — making it the single most important environmental health risk factor on the planet. To put that in perspective, outdoor and household air pollution combined accounted for roughly 12% of all deaths in 2019. That's not a marginal issue.

What changed in 2021 is that WHO cut the recommended safe limit for PM2.5 in half — from 10 µg/m³ down to 5 µg/m³ annually. That's not because the science changed dramatically; it's because the evidence had accumulated to the point where the old threshold couldn't be defended anymore. Research now consistently shows harmful health effects at concentrations well below what was previously thought safe, with no observable threshold below which exposure carries zero risk.

The indoor angle is what I think gets underestimated. Studies show people spend an average of 87% of their time indoors. Sources like cooking smoke, gas stoves, candles, incense, poor ventilation, and outdoor pollution infiltrating through windows can push indoor PM2.5 to levels far above WHO guidelines — sometimes dramatically so. Burning a candle in a closed room can generate PM2.5 concentrations above 1,200 µg/m³. The outdoor air on a moderately polluted day is cleaner than your living room when dinner is on the stove.

The good news is that the mitigation tools we have actually work. A peer-reviewed study published in MDPI's International Journal of Environmental Research and Public Health found that HEPA air cleaners reduced indoor PM2.5 concentrations by an average of 16.3 µg/m³ — cutting the indoor/outdoor PM2.5 ratio nearly in half (from 76% down to 39%). A separate study published in Toxics (2025) tracked 67 low-income households over 12 months and found HEPA/carbon filter purifiers reduced PM2.5 by 45%.

WHO Global Air Quality Guidelines 2021
https://www.who.int/europe/news/item/22-09-2021-statement-launch-of-the-who-global-air-quality-guidelines

[hunter]

1. I'm wary of my gas oven and stove.

When I cook I always turn on the range hood fan to vent the fumes outside. I also crack open a window away from the exhaust.

If it was up to me I'd have an induction cooktop and electric oven.

Fossil fuel gas is dangerous. Our utilization of it is destroying the natural environment as we know it. Unfortunately we are very well trained to ignore all of that.