Where can I find the technical documentation of the /json endpoint when accessing a PurpleAir sensor locally over the network? I’ve checked the API documentation , but the fields do not match. Where can I find the documentation for the JSON fields? In particular what does the pm2_5_atm and pm2_5_cf…

We don’t currently have documentation for everything on the /json endpoint. However, some of the fields are similar to what’s recorded to the SD card . This includes both pm2_5_atm and pm2_5_cf_1. Note that there may be some differences between the SD card data, and what’s obtained via /json. We’ll …

Please post when documentation is available for the json data. I’m writing queries for an sql db for an educational demo. Thanks

Aha, so atm is for outdoor or “atmospheric” conditions and cf1 is for indoor conditions. Does that mean the sensors use cf1 to calculate their AQI when set to indoor, or do all sensors use atm to calculate the *_aqi values?

Hey Josh, I’m developing a weather station data app for a client, and trying to include data from their Purple air device. I’d like to pull data from the device directly, rather than hitting the web API. Do you guys actually have a plan to release some basic JSON API docs? I’ve read on the forums …

Hi @till The PurpleAir map will display CF1 data for indoor sensors and ATM for outdoor sensors based on their registration data. You can find more information on these categories in this community article: What is the Difference Between CF=1, ATM, and ALT? .

:heart: Thank you so much for providing this documentation, it very much helps to be able to understand the fields and how they relate to each other! This will make it much easier to integrate the device into home automation and such!

Local JSON endpoint documentation

Data

Josh_PurpleAir (Joshua) December 19, 2023, 7:23pm 7

@till @K7FZO @DD_Josh

Documentation is now available in our Local JSON Documentation article.

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Sensor JSON Documentation Data	3	1860	March 11, 2026
API data varies from Local Data API	3	166	March 15, 2025
Documentation on SD Card CSV data Data	1	627	November 29, 2023
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Pm2.5 data differs between JSON and API Data	2	167	January 27, 2025

Local JSON endpoint documentation

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