OpenAQ vs PurpleAir

Verdict

These two are more often used together than against each other — OpenAQ explicitly lists PurpleAir as one of its integrated data sources — but they answer different questions and are worth separating clearly.

PurpleAir sells the sensor. Every registered unit streams PM1/PM2.5/PM10, temperature and humidity readings to PurpleAir's own free public map, and PurpleAir's business model is the one-time hardware sale, not the data itself. If you want a specific, local, real-time reading from a device (yours or a neighbor's), PurpleAir's map is where you go.

OpenAQ aggregates. It is a nonprofit, funded by grants and donations, that harmonizes government monitoring-station data, research networks, and low-cost sensor feeds — including PurpleAir's and Clarity's — into one standardized, free API covering pollutants like PM2.5, PM10, NO2, SO2, O3 and CO across tens of thousands of stations in over 100 countries. If you want to query many sources at once, or need a jurisdiction's official government reading alongside community sensor data, OpenAQ is built for that; it is a data layer, not a hardware product.

Choose PurpleAir if

• You want to buy a sensor and see your own readings on a public map, in addition to nearby community readings.
• A simple, visual, real-time local map is all you need, with no API integration work.

Choose OpenAQ if

• You are building something — a research dataset, an app, a report — and need one API instead of stitching together national government sources plus PurpleAir plus other feeds yourself.
• Provenance matters to you: OpenAQ documents source and instrument type per station, so you can tell a government reference monitor apart from a low-cost sensor feed within the same dataset.
• You want government and low-cost data in the same query rather than a single sensor network's view.

What they share

Both are free, and both rely on the same underlying reality: low-cost optical sensors (including the PurpleAir units OpenAQ ingests) read high during smoke and high-humidity events relative to reference-grade instruments, and neither vendor pretends otherwise. Coverage from both is uneven by region — dense in areas with many registered sensors or government stations, sparse elsewhere — so check what actually exists near your location of interest before treating either as a complete picture. See IQAir vs PurpleAir for how PurpleAir compares against a rival hardware vendor rather than an aggregator.