So it looks like the SDS011 is the preferred way to go ATM for the particulate sensor. Reasons:

  • it's laser based, and therefore more accurate than the optical PPD42 sensors,
  • it's a standard piece of kit that lots of big projects are using, which is important for support and producing comparable data,
  • it's not too expensive, although it's more than I would like.

That still leaves the gas sensors to decide on. I have the MQ135 sensor, but I need to evaluate if the following are worth having on board specifically because of waste water plant exhaust gases (there is a strong unpleasant odour from the Eastbourne Waste Water Works when the wind is in the wrong direction), and because of a multitude of indeterminate environmental influences in a Jakarta gang. The broader the spectrum of sampling the better placed we will be to understand what is going on.

MQ2: hydrogen, LPG, methane, carbon monoxide, alcohol, smoke or propane.
MQ3: alcohol vapour (eg. breathaliser)
MQ4: methane, CNG gas
MQ5: natural gas, LPG
MQ6: LPG, butane
MQ7: carbon monoxide
MQ8: hydrogen
MQ9: carbon monoxide, flammable gases
MQ131: ozone
MQ135: ammonia, nitrogen oxide, alcohols, aromatic compounds, sulfide and smoke
MQ136: hydrogen sulphide
MQ137: ammonia
MQ138: benzene, toluene, alcohol, propane, formaldehyde gas, hydrogen

... and there are many others.