I believe it would be both valuable and interesting to see a PurpleAir map with a selectable layer for “WHO PM2.5” (WHO = World Health Organization) that shows green only at or below 5 micrograms/cubic meter. Not sure what yellow or red or purple colors would indicate, but maybe we could put our heads together to figure it out? Here’s some info on their air quality guidelines: https://www.who.int/news-room/feature-stories/detail/what-are-the-who-air-quality-guidelines
Excellent idea - I would like to have that feature also.
The specifications you linked prescribe annualized exposure, not immediate or hourly exposure. You could develop a map using PA data to plot compliance with the guideline on a yearly basis. That said, no country reporting data for 2016 (the latest WHO has published in their Air Quality Data Portal) meets the new 5 ug/m3 guideline.
There’s a list of interim targets in the guidelines you could use as a basis for a color key.
The WHO 24 hour standard is 15 μg/m3 24-hour mean (see Ambient (outdoor) air pollution) at the 99th percentile (i.e. 3–4 exceedance days per year).