Consistency of Airnote's readings under full sun

Hi Rob,

From its well shadowed installation in a recessed balcony of the 7th floor, my Airnote gives not only consistent values of the air temperature and humidity (checked with another meter), but also more reliable readings of the PM. No GPS lock, but this is another story…:slight_smile:

In fact, desiring to verify the effects of full sunlight on the measured values, last Sunday I moved the device in full sun for a while. Initially the air temperature was slightly above +30°C and the relative humidity 36.8%.

After about one hour, the temperature given by the Airnote was risen up to more than 43 °C, while the relative humidity dropped down to 20.6%.

In the same time, and as long as the internal temperature of the device remained high, also all three PM values were dropped down by an important percentage.

At this point I stopped the test and placed the Airnote back in its “shadowed” position. The measured air temperature values (that could have risen even more under the sun) went slowly back to the real ones, as well as the humidity and the three PMs, as shown in the attached screen capture.

This makes me think that to get consistent readings of all these parameters, the internal temperature of the Airnote should be kept as much as possible equal to the external air temperature, avoiding the localized overheating of the device’s internal ambient due to the direct sunlight. It’s something I noticed also when beta-testing Safecast’s first air quality control prototype. Therefore I surrounded Safecast’s Pelican case with a shroud keeping its sides sufficiently distanced from the case.

What do you think about this problem?




Thanks for the observations. It seems to me the issue is inherent to the design of the AirNote. The compromised made in the layout/construction/price/etc…


You’re welcome, Rob.

As an old hardware designer I do agree with you. In fact all this must not have been an easy compromise, keeping also in mind the cost of the product.

I suggest to deepen the analysis by performing independent tests in different ambients and with different PMs. It should give a more accurate idea of how much the particulate measurements are influenced when the device is under full sun, and what are the best solutions to mitigate these effects.

The single experience I made tells me that with the current device a full sun exposure should be avoided. Temperature and humidity readings become totally wrong, of course. But also the PM measurements seem to be seriously affected (reduced, as if the air was much cleaner). At least, this is what happened at the low PM levels I recorded.

Anyway, and waiting for some news and suggestions, I’ve decided to keep my Airnote permanently away from direct sunlight. To survive, it will get a 5 V supply through an USB cable.

Best regards,



Good news, a laboratory, AQ-SPEC in California, is performing independent tests of Airnote as we speak. When analysis is done they’ll post the results on their public summary page.


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Thank you Carl, and please let me know when the results will be available.

In the meanwhile I will repeat several times my previous test to collect more data.