The unit is fed from a 24 volt supply and POE injector/splitter.
Actual voltage arriving at uRad is about 20 volts when using the 24 volt supply.

The center portion of this graph is with the 18-volt battery supply (3×6.3).
The right hand side is back on the 24 volt supply with some added filtering – I can do more.
I can also try lowering the voltage, as I found everything else on the system works at 18 volts.
You can see the readings average about the same values with either supply.

I an quite sure the O3 sensor is responding to other compounds in the air. I found it is quite sensitive to alcohol and the forest here emits natural compounds that are chemically similar to alcohol. The second photo shows the month of September. Readings are rarely below 100 ppb and tend to show a peak right after it rains, when soil bacteria naturally emit a compound that the O3 sensor seems to detect quite well.

Ken