Sensor Maintenance

This article contains information on maintaining a PurpleAir sensor’s laser counters, which collect particulate matter data. If your sensor is experiencing issues with temperature, humidity, or VOC readings, try the steps in our BME Troubleshooting article. If your sensor isn’t powering, try the steps in our Power Troubleshooting article.

Once your sensor has been in service at the installation location, it becomes exposed to foreign contaminants. We expect the sensor to contact airborne particulate matter. But undesirable contaminants may impede the function of the sensor.

We do not recommend a regular cleaning schedule for PurpleAir sensors, and no preventive maintenance is required. If one of the laser counters is not reporting as expected, is downgraded, reporting high, not working, or spikes erratically, then it is possible that one of the laser counters in your sensor has become congested with debris, an insect, or a spider.

If a single laser counter is consistently reading at or near 0, the issue can be caused by a broken fan in addition to insects or debris.

Cleaning the Laser Counters

If necessary, clean out the laser counters: First, power off the sensor so that the laser counter fans stop spinning. Place a shop vacuum or traditional vacuum hose on the bottom of the sensor for 2-3 minutes. Clear out the laser counter with canned compressed air if further cleaning is necessary. For PA-II and PA-II-SD sensors, focus on the four collinear holes on each laser counter (see image below). For PA-I edition sensors, focus on the rectangular hole on the side opposite the fan. For the PurpleAir Flex, focus on the rounded rectangular hole on each laser counter.

For sensors with two laser counters, the A channel is the laser counter farthest from the USB port. The B channel is the laser counter closest to the USB port.

Note that increased airflow speed can cause the fan to spin at a much higher rate than recommended, which can damage the laser counter. We recommend physically blocking the fans in a device with a toothpick or something similar to avoid this issue during maintenance.

Optional Steps

The following cleaning is optional, and is not an official part of our troubleshooting steps.

It is possible that debris caught inside a laser counter can persist after cleaning with a vacuum or compressed air. This type of debris is usually something like a spider web. Given that the previous steps were unsuccessful, a more in depth cleaning could solve the issue. The following article outlines how to open up and clean a laser counter:

Power Issues

Although rare, it is possible for power problems to cause erroneous readings. If your sensors readings are still erroneous after cleaning the laser counters, we recommend the following troubleshooting steps:

  • Plugging the sensor into a different power outlet
  • Using a different power cable

Replacement Laser Counters

Information pertaining to replacing the laser counters in your device can be found in our Sensor (Laser Counter) Replacement community article.

Learn More

Learn more about calibrating PurpleAir sensors .
Learn more about downgraded channels.

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Should the sensor be powered down before applying the vacuum to the vents? Or can it stay powered up for this maintenance?

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Hi, @WhatsInYourAir, we recommend powering down the device before vacuuming and using compressed air. This is so the fans stop spinning and help prevent damage to the laser counters.

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