(2) Inhaled air has 21% oxygen.After absorption of oxygen in thealveoli, it comes down to 17%.Carbon dioxide in the inhaled air isvery little (0.04%). Blood releasescarbon dioxide in to the alveoli andthe amount of carbon dioxidecoming out increases to 4%.Nitrogen in the inhaled air is about79% and it comes out unused.Inhaled air has very little amount ofwater vapour but the air coming outgets a lot of water from the moistsurface of alveoli, bronchioles,bronchi, trachea and the nasalpassage. Its temperature is equal tothat of the body temperature.