So - this could be pretty - if someone wants to help with bitmaps.  I played with them a bit, using the resources on Adafruit Learn however I'm not thinking I'll mess with more than maybe choosing some other font.   The real benefit of sensor devices like this are not the instantaneous reading - rather being able to capture time-series data and looking at trends is more valuable.  You can spot patterns that indicate inadequate ventilation - say building up over night so you get a nice concentration increase before anyone awakes and opens doors or windows.   

     I use natural gas in my home ( built in 1943 ) and its pretty obvious when I return home after the house has been closed for even just a couple of days.  I wondered about this stuff for years, called it the "farm-house smell" as I've always noticed it since I was a child.  Its not exactly the scent they use in the gas, at least to my evaluation. 

    Eventually I learned about the special characteristics of natural gas, that it is not really treated or distilled like propane.  That it can contain lots of interesting molecules.  Its not like it freaks me out, I'm just curious.  And I sleep near an open window.  I digress.  

    There is enough memory on the M4 to maybe save some number of sample passes - some amount of local preprocessing is perhaps also possible as Temperature and Humidity can introduce errors in the measured values in some of the sensors.  The electro-chemical senors may need more work to be linear over temperature and/or humidity.  Finding the range of those two in the time series will tell if that is needed.

But to have the data - we need to speak with a broker. A mqtt broker.