Well, perhaps not everywhere. The diurnal variability of PM2.5 is a known thing. The layer that I referred to in my previous post is described as the “planetary boundary layer” (PBL) in the referenced study. How that varies during the day is discussed on pages 8-10 and it is noted that the maximum concentration of PM2.5 is seen at dawn and the early morning hours for most of India during this time of year. This is mainly due to the diurnal variation in the PBL, its expansion during the day diluting the particles. It’s not true everywhere though.In short. Pollution is higher at 4am to 10am or early morning and this is official and occur everywhere? We tend to think pollution is greater at mid day as there are more and more cars.