A: When looking at the map graph, there may be a channel reading slightly lower or slightly higher than the other channel, but the pattern of the reading is similar.
Variations between the two internal channels in PurpleAir sensors can be typical of low-cost particulate sensors, especially at lower PM readings.
PurpleAir calculates the Air Quality Index (AQI) and confidence score based on the average of the two channels. If your sensor’s readings are generally in line with nearby sensors on the map and the confidence score is 85% or higher, your sensor is likely performing accurately.
That said, some variation can be attributed to factors such as:
- Sensor age – Laser counters typically last around two years, but their lifespan can vary depending on environmental conditions (e.g., humidity, dust exposure, temperature extremes).
- Contamination – Dirt or debris in one laser counter channel can lead to inaccurate or unstable readings.
If you notice:
- One channel reading abnormally high
- A low confidence score
- A channel has been downgraded
We recommend reviewing our Sensor Maintenance article for guidance on cleaning and evaluating your sensor’s performance.