The adverse effects have been traced mainly to small particles with an aerodynamic diameter of 10 microns or less, which can reach deep into the lungs. Smaller particles can go even deeper into the lungs, where those that are still tinier can enter the blood stream. These particles can disturb the lungs physically and chemically. They can directly irritate the lungs, and they can carry toxic heavy metals and other pollutants. The average person breathes several million liters of air a year.
Children take in even more air relative to their body weight and size.
Those who exercise heavily or work hard, of course, breathe even greater volumes of air. Breathing finely polluted air can produce slow and insidious effects or devastating and immediate ones. Over a lifetime, regular breathing of contaminated air can impede the ability of the lungs to breathe in oxygen and get rid of pollutants. Polluted air can cause immediate or acute effects ranging from asthma attacks to death in those whose lungs are already weakened. Both scenarios assume that energy use and energy efficiency in the developing countries continue to increase to meet the needs of economic growth.