Please note that the Air Pollutant Index reported by the DoE is calculated based on the 24 hours running average of the most dominant pollutants (including PM2.5, PM10 and Ozone). This can make it really difficult to find out what the actual air quality is in real time. The best practice is to report real-time air quality using hourly data, which is what most EPA worldwide do.
For instance, during a period of Haze, where the Air Quality Index can deteriorate significantly and fast, the published Air Pollution index is most likely lower than the actual pollution. Similarly, when the air polution decreases, the Air Quality Index can still be very high although the pollution is gone.Read more here.