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