No the above ranking is not an average. It is the situation of a specific time, right now at 22:43, February 3rd, 2018.
But it is 492 in PM2.5 air quality index! It means you need industrial-grade mask to breath outdoor, anything else is doing serious harm to yourself. Don’t take this lightly. Check the latest details here.
The accepted safe range of PM 2.5 index is 50, up to 100 it is somewhat ‘ok.’ When it goes beyond 100 you should take action to avoid outdoor exposure.
In Dhaka, below 100 is a luxury, you can see two digit ratings only during the monsoon. I have set my personal limit at 200. If it is above 200, I wear a mask, and I specifically avoid riding Pathao/bikes. If I’m Ubering, the windows are locked and AC running.
Install the AirVisual app or visit this page regularly before you go out in this city!