Sensors & sources

Every place we pull air-quality data from, and how fresh each reading is.

Tap any sensor for its 48-hour history, caveats, and limits.

Understanding your sources

No two sources measure the same way. Live neighborhood sensors react instantly but are low-cost; official monitors are accurate but average over hours; models cover everywhere but smooth over local spikes. When they disagree during smoke, trust the dense live sensors — that's why our "near you" headline uses the closest PurpleAir average.

Home station sensor

Live — polled every few minutes, essentially real-time.

A low-cost optical PM sensor: it counts particles and estimates mass, so it can read high in fog, high humidity, or dense smoke.

PurpleAir sensor

Live — updated roughly every couple of minutes.

Optical low-cost sensors estimate PM mass from particle counts; they can over-read in high humidity, fog, or heavy smoke.

AirNow (EPA) official

Reported as a NowCast — a weighted rolling average of the last several hours — so it lags a fast-changing plume by design and updates hourly.

NowCast smooths sudden spikes: during a rapidly worsening smoke event it can read well below a live neighborhood sensor.

WAQI station

Typically hourly, depending on the contributing station.

It is the nearest STATION's value, which may be miles from you and in different air.

Open-Meteo model

Its 'current' value is a modeled, hourly-averaged estimate that can lag a real spike by an hour or more.

Modeled on a grid cell of several kilometers — it smooths over local hotspots and can under-read a fast smoke plume that ground sensors already see.

OpenWeather model

Modeled hourly value; can lag real conditions.

Gridded model output, not a local sensor — smooths over local events.

Sensor locations

Source	Provenance	Sensor	Location	Pollutant	PM2.5	PM10	AQI	Level	Updated
AirNow	Official (NowCast) Lagging	airnow_Southwest_O3	Southwest	Ozone	—	—	18	Good	Oct 01, 08:00 AM EDT
Home	Current (Airsight)	ha_purpleair_front_porch	Home	PM2.5	0.1	0.3	0	Good	Nov 14, 02:40 PM EST
Open-Meteo	Current (Airsight)	openmeteo_point	~0.0 km	Ozone	0.2	0.2	32	Good	Nov 14, 02:00 PM EST
OpenWeather	Current (Airsight)	owm_st_joseph	—	Ozone	1.2	2.4	31	Good	Nov 14, 02:41 PM EST
PurpleAir	Current (Airsight) Lagging	pa_119777	~19.1 km	PM2.5	16.6	—	60	Moderate	Jul 20, 03:31 AM EDT
PurpleAir	Current (Airsight) Lagging	pa_123741	~17.4 km	PM2.5	21.9	—	72	Moderate	Jul 20, 03:41 AM EDT
PurpleAir	Current (Airsight)	pa_181673	~26.4 km	PM2.5	3.2	—	13	Good	Nov 14, 02:41 PM EST
PurpleAir	Current (Airsight)	pa_186629	~23.5 km	PM2.5	0.3	—	1	Good	Nov 14, 02:31 PM EST
PurpleAir	Current (Airsight)	pa_186651	~20.7 km	PM2.5	0.0	—	0	Good	Nov 14, 02:41 PM EST
PurpleAir	Current (Airsight)	pa_250659	~7.8 km	PM2.5	1.5	—	6	Good	Nov 14, 02:41 PM EST
PurpleAir	Current (Airsight) Lagging	pa_281252	~32.6 km	PM2.5	0.0	—	0	Good	Nov 13, 05:41 PM EST
PurpleAir	Current (Airsight) Lagging	pa_294923	~1.9 km	PM2.5	17.5	—	62	Moderate	Nov 04, 08:21 PM EST
PurpleAir	Current (Airsight)	pa_309688	~1.1 km	PM2.5	0.0	—	0	Good	Nov 14, 02:41 PM EST
WAQI	Station (WAQI)	waqi_south_bend_shields_dr_indiana_usa	South Bend Shields Dr Indiana Usa	Ozone	—	—	18	Good	Nov 14, 02:00 PM EST

Reading the badges

Official (NowCast) — AirNow's reported AQI (a rolling average from EPA reference monitors).

Current (Airsight) — current-conditions AQI we compute ourselves from raw concentrations (instantaneous, no averaging).

Station (WAQI) — nearest-station aggregate from the World Air Quality Index.

Lagging — the reading is stale, or a model value a fresher real monitor contradicts.