A new Raspberry Pi HAT is about to launch on Kickstarter “Raspberry Pi Air Monitoring HAT | Real-Time PM Sensor For Raspberry Pi”, which is amazing as well as very useful HAT for now a days in polluted cities and other polluted areas and also a good product for learning as well.
Check here: https://www.kickstarter.com/projects/amritsingh/air-monitoring-hat-real-time-pm-sensor-for-raspberry-pi