Updating the color on maps.sensor.community to reflect the new WHO recommendation for PM "safe limits"

[MagTun]

The problem: sometimes the sensor on the map are green but the air looks healthy but the level of pollution is (relatively) high.

This is even more problematic as the WHO has recently updated their "safe limits" for PM10 and PM2.5 as explained here. The transition from the color green to yellow on the sensor maps should reflect these new recommendations especially for PM2.5 which is much lower now

Edit: It's important because "the harm increases fastest at the low levels of pollution." A jump from 5 to 20 micrograms has a worst effect than a jump from 100 to 115 micrograms. (source)