IOT Pollution monitoring HELP!?

Im torn between the two- Should I used Pi or Arduino for outdoor pollution monitoring?
I have roughly a budget of $120 USD per node.  Can I use both of them together?

- If pi. What do you do about battery conservation?
Pushing data to a webpage recomendations?
Uploading data?

What sensors should I use? Ive seen someone trying to sell a single CO2 sensor for $50 USD?!?
CO2, NO, CO, NO2 sensor suggestions?
Ive been looking at grove
Some will be battery powered. others by the mains. im going to try 3D print a case for weatherproofing.