India doesn’t do data
Greenpeace’s Delhi data derives from the only three air monitoring stations for which historic PM2.5 data is available to the public.
There are a total of 16 sites collecting data in Delhi, as well as the US embassy, but the Meteorological Department doesn’t archive, and half the stations run by the city’s Pollution Control Committee don’t monitor PM2.5.
There’s also missing air readings for 56 days from last year.
This is all pretty poor compared to Beijing, where 14 stations around the city provide annual data dumps, with no missing days — though there’s also an archiving problem in China.