The library
A small, slowly-growing collection of source-cited primers about air pollution, especially fine particulate matter (PM2.5) — what is measured, who measures it, and what the headline numbers actually mean. Plain English. Free to copy, translate, and republish.
Every external source on every page is HEAD-probed once a day by our curator Lambda. Broken links are repaired or dropped automatically.
Primers
Read-through pieces. Each one is roughly 600–900 words, source-cited, focused on a single concept that comes up everywhere in air-quality coverage.
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What PM2.5 is and why the WHO 24-hour guideline is 15 µg/m³
The single most important indicator in modern air-quality coverage. What “PM2.5” actually refers to, where it comes from, why the World Health Organization revised its guideline downward in 2021, and what the gap between household and ambient sources means for policy. Foundational.
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What this site does not cover, and why
Chemtrails, ozone-generating "ionizer" air purifiers, essential-oil diffuser health claims, and brand-by-brand purifier rankings are not on the map. Here is what the WHO, US EPA, and named atmospheric-science bodies actually say, in their own words.
How to use this library
Everything here is published under Creative Commons BY-SA 4.0. You may copy, translate, adapt, and republish any of it — please keep the source citations intact, and please publish your derivative work under the same licence so the next person can keep building.
If you are a teacher, an after-school program, a community group, a parent, a librarian, or a person who works with kids: please take what is useful and pass it on.
If you find an error, an out-of-date source, or a claim that overstates the underlying evidence: how to flag it.