A: PurpleAir PA-II and PA-II-SD sensors contain two laser particle counters that measure real-time particulate matter and report as Channel A and Channel B.
If one of the channels appears to be reading improperly, it can be downgraded. This is either done automatically by our systems or manually by PurpleAir staff. A downgraded channel will not be used in its sensor’s data average and will lower its sensor’s confidence score.
You can tell which channel is downgraded by clicking on a sensor’s map marker.
If a channel on your sensor appears to be incorrectly downgraded, send an email to contact@purpleair.com for assistance.
Learn more about channels reporting high, not working, or spikes erratically.
Learn more about sensor maintenance.