How bad is Delhi-NCR’s air quality? Why was GRAP-1 imposed and what are the measures?

Delhi’s Air Quality Index (AQI) stood at 278 on May 16, within the ‘Poor’ category. Forecasts by the India Meteorological Department (IMD) and the Indian Institute of Tropical Meteorology (IITM) have predicted that the AQI will remain in the lower end of the ‘Poor’ range on May 17 as well.