Cumulus Support

I'm very much aware that low cost air quality sensors like the WH41 have their limitations. But still ...

Here is the situation: for a few nights now I have observed unusually high AQ readings while the air quality was actually fine. I'm now trying to figure out what the reasons for these mis-readings are. First off: it's not the battery (fully charged) and not the humidity (around 70%, no snow or flurries).


The Ecowitt web site states:

When the Dew Point is close to the outdoor temperature (T - D < = 2C), the PM2.5 reading will be very high (which is not the real condition). If mind, please don't purchase.

Possible, but this can't be the (only) reason, since the temperature/dew point difference was below 2°C most of yesterday morning and the AQ readings were not affected (the light green shaded areas are below 2°C difference).

Another reason – or a combination with the above – could be the temperature. False readings only occurred at temperatures below -6.5°C. But shouldn't an AQ sensor specifically built for outdoors work at these temperatures. What will happen when it hits -30°C in a few weeks' time?
And why is it happening only at night? I've been brainstoring with my wife and we now believe it's a Sasquatch (the North American version of a Yeti) lying down for the night under the sensor. Maybe some of you can find a better explanation ...

On a related issue, it would be nice to be able to set a spike limit for AQ sensors to catch errors like these:

Would people be burning their stoves at night? Smoke from wood fires are known (under favorite wind conditions) to give high levels of PM.

HansR wrote: ↑Wed 24 Nov 2021 6:46 pm Would people be burning their stoves at night? Smoke from wood fires are known (under favorite wind conditions) to give high levels of PM.

Sure there are wood fires, but that would be much more of a problem during the day. In the evening you usually let your woodstove burn down, except it is REALLY cold. If it was wood fires I would expect a peak between 6 and 8 AM.

yeah tbt i got mine today and im sending it back as it crap i got the davis air link one for out side but this one is something like a toy

Like Hans mentioned it might be directed smoke.

I was about to draw a parallel to the spike I was seeing until I saw your time scale.
Mine I believe were light leaking into the sensor chamber.

Take a look at my post on WXforums

My spike moved from morning to afternoon when I spun the sensor 180°.

Also worth noting, is that the sensor that's pictured early in the thread is different to what I see in mine.
Not sure what sort of time span that involved.

Edit:- you need to scroll back to see my early posts with graphs of the spikes.

I think you also need to look at wind speed & pressure, I find my sensor (homemade using a SDS011) does exactly what yours is doing some nights, usually when the wind is light or there is an inversion. I can only assume that any particulate matter, possibly from wood burning stoves, gets trapped at lower levels and slowly drifts to your location overnight or an increase in water droplets would have a similar effect, a slight increase in wind and the values drop.

I do not know if this has anything to do with readings but my readings were somewhat erratic but I also noticed that the rechargeable batteries that Ecowitt provided were not very good at holding a charge .

So I bought so higher quality rechargeables (Panasonic Eneloop that are used by camera professionals https://www.amazon.co.uk/gp/product/B00 ... UTF8&psc=1 ) and replaced the Ecowitt ones.

Immediately the readings improved and were not subject to the wild fluctuations and the new batteries also held their charge much better.