Are there any changes between the value of AQHI during the day and night?

The Air Quality Health Index is computed using the amount of
various air pollutants like nitrogen dioxide, ozone, and fine particulate matter. The amount of
all these pollutants is different during the day and the night. This can be attributed to several
reasons.

Ozone is formed at ground level by chemical reactions that
take place between oxygen molecules due to ultra violet radiation in sunlight. As the UV
radiation is not present at night, the amount of ozone formed is reduced. Nitrogen dioxide and
fine particulate matter produced by smaller vehicles is also higher during the
day.

Some reasons why the amount of pollutants might increase at
night include the cooling of the air that moves air pollutants present at height altitudes
towards the ground. Also, some sources of pollution like power stations work throughout the
night. As the number of heavy vehicles traveling is increased at night, this can also increase
the level of some pollutants at night.