Getting started in Citizen Science: monitoring pollution

I've always thought Earth will fall in my lifetime - is that weird? The rise of Extinction Rebellion & coverage of recent environmental catastrophes has only fuelled this feeling. So, obv, I decided to attach a particulate sensor to the side of my flat so I could at least angrily Tweet the data from it to make myself feel better. I won't go into actually building the the thing in this post because...