This page describes how BreatheCheck is actually produced. It exists because “trust us” is not a method, and because a reader who finds a number here that disagrees with their own instrument deserves to know how ours was made before deciding which to believe.
Two different things are published here, and they are made differently
The readings are collected by machine, hourly, and published without anyone looking at them. Nothing in that path is reviewed before it reaches the page, because a number that waits for review is a number that is no longer current.
A scheduled job pulls the regulatory observation from EPA AirNow, the median of nearby outdoor PurpleAir sensors corrected with the published US EPA formula for PA-II units, and modelled pollutant and UV values from Open-Meteo. What protects that number instead is what it refuses to do: a feed that fails renders “we don’t know right now” and the last good reading with its timestamp, never a stale number dressed as live. A page whose data has not refreshed in three hours stops calling itself live.
The prose is written against a brief and reviewed before it ships. Drafts are produced and checked by an automated editorial pipeline, not by an unreviewed generator. The review stage exists to do one job: verify every concrete claim against a source and delete what cannot be verified. It regularly rewrites drafts and it deletes claims. A recent pass caught a tree-canopy figure that was current in 2008 and stale by 2023, a lake-effect mechanism attributed to the wrong shore of Lake Michigan, and a comparison that was false for one city in the list. Those are the errors this stage is for.
We do not claim a human reads every sentence before it publishes. Saying otherwise would be the easy thing to write and would not be true.
What gets attributed, and how
Every threshold on this site is either an agency classification or a reported behaviour, and the two are labelled differently every time.
An agency number says whose it is: “EPA classifies 101–150 as Unhealthy for Sensitive Groups” is cited as an EPA classification, and it is never rewritten into “AQI 120 is dangerous for you.” A reported number says who reported it: a runner’s own cutoff from their own log, a parent’s, the figures parents and staff gave for their daycare in one thread. Those are useful precisely because they are what people actually do, and they are worthless if presented as policy. When a page shows both, it says which is which.
If a number here carries no source, that is a defect, not a style choice. Report it.
What we will not publish
- Medical advice. We describe what a number means and what an agency says about it. Whether it is safe for you specifically is a question for someone who knows your history.
- A tested-product claim we have not earned. We have not run a purifier through a chamber test. Where the site discusses equipment it says where the figures come from and does not imply we measured them.
- An invented number. No estimated statistic, no backfilled history, no figure whose source we cannot name.
- A stale reading presented as current. This is the one lie the site could tell without anyone noticing, so it is the one guarded hardest.
- Coverage we do not have, described as coverage. Metros we measure but do not publish are named as measured and unpublished, with their live reading and no link.
Errors, and what happens to them
Every correction gets a dated entry on the public corrections log, permanently, and it is never edited away quietly. A page that has been corrected carries a dated link back to that entry, so a reader sees the history rather than a clean surface pretending nothing changed. That link is generated from the log itself, so a correction cannot be recorded without the page showing it.
The fastest way to get something fixed is to tell us what you saw — which page, and what your own reading said. Leaving an email address is optional; reporting a wrong number should not require identifying yourself.
Money
Nothing on this site earns anything. No advertising, no affiliate links, no sponsored placements, no subscriptions. Where a page names a portable HEPA unit or a Corsi-Rosenthal box, that is the equipment people described using, and no link on this site pays us when you buy one.
That is a deliberate choice, and the practical consequence is that a recommendation here cannot be bought. The full version is on how this is funded. If that ever changes, the disclosure appears before the recommendation, not after it, and the change gets a dated entry in the corrections log.