Ozone pollutants and health effects

Dear Tom,
On many days my sinuses drain and my throat really burns. Those days seem to correspond with days when the critical pollutant is ozone. Can you explain why?
—Paul Kouba,

La Grange
Dear Paul,
Ozone (chemically O3, a form of oxygen), is an invisible pollutant whose concentration increases sometimes to dangerous levels on hot, sunny days. (In the upper atmosphere, however, ozone is important in preventing dangerous levels of ultraviolet radiation in sunlight from reaching the surface.)
Breathing ozone can result in several negative health effects, some of which are respiratory: pain in the chest when taking a deep breath, chest tightness or shortness of breath, coughing and throat irritation. Ozone can irritate the airways, especially in children, the elderly and in people active outdoors.