Icon request: Standard icons for air-quality indicators/sensors

[Wendelstein7]

Hi all! Since a while we have had the 'CO2'-icon, perfect. With the rise of IoT devices, amongst which are devices which measure some popular air quality levels, I think it would be perfect to add the most popular few of those to the MDI-library. This'll enable developers of apps and frontends to easily use buttons/widgets/cards with icons for viewability and consistency.

Popular sensors include the Awair Element and others, and these are the sensor values that I see most:

• Humidity - already included - could be improved by having its own dedicated icon rather than using a water drop
• Temperature - already included
• CO2-levels (Carbon dioxide, in ppm) - already included
• VOC-levels (Volatile Oranic Compounds, in ppb) - could be added!
• PM2.5-levels (Small particles in μg/m^3) - could be added!

I hope this helps! Good luck :)