Why do some field descriptions have a time descriptor but no formula descriptor?

Quick question for the community - what does it mean if there’s a time attached to the field description but no formula specifier? I understand the difference between pm2.5_atm and pm2.5_cf_1. It’s not clear to me how pm2.5, pm2.5_10min, pm2.5_30min, etc. – which do not include atm or cf descriptors – play into this.

Particulate matter fields without a specified density estimation automatically select one based on the registered location_type. This mirrors the PurpleAir Map, which uses the same method to obtain a value for the Raw PM2.5 datalayer. “atm” is used for outdoor sensors and “cf_1” is used for indoor sensors.

Fields that do this are currently only queryable from the real-time API, as the location_type field is not available in historical data.

We’ll update the API documentation so this is more clearly reflected.