I have noted the readings on my PurpleAir sensor become higher that expected during snow conditions accompanied by strong winds.
My readings track government sensors fairly well much of the time but during windy snow events my reading become higher than government readings.
Could my sensor be responding to snow that is entering the sample chamber? Does anyone have experience with this possible measurement effect due to snow in windy conditions?
Or are the higher reading I see during snow and wind events a true representation of local air quality and there is some local source that I have not identified?
I am wondering if providing some amount of wind and weather shielding for my sensor is a useful step to take. Does anyone in the community have esperance with this?
Having a better understanding of what may or may not affect PurpleAir’s data makes the data more valuable.
Bob J.
You likely have it right that it is snow or ice crystals getting into the chamber. A similar thing happens during fog. The PA sensor can’t tell the difference between particles of dust and particles of water and just tells you what it sees. To compensate for error from fog, the US EPA adjustment uses the humidity sensor reading to correct the reported PM2.5.
I’d recommend against any sort of shielding for the sensor. Without careful design, the shield will encourage reintake of sampled air and result in erroneous readings.
Periods of error due to weather are usually short-lived and can be detected by other methods. If you frequently get snow and have problems with the readings spiking, it may be worth exploring whether you can move the sensor to a wind-sheltered area that still has good air exchange, like the leeward side of the house, relative to prevailing winds.
I did notice this too. We have lake effect snow, super light snow that just blows around and does not really drop to the ground. My readings were super high. I figured it must be the snow.