This is because most pollen is released in the morning and rises into the air with the heat of the day.
(This; is; because most pollen is released in the morning and rises into the air with the heat of the day) (most pollen; is released; T:in the morning) (most pollen; rises; into the air)
This most pollen most pollen
is is released rises
because most pollen is released in the morning and rises into the air with the heat of the day
T:in the morning
into the air