At normal concentrations it is colorless and odorless.
Ozone is a major component of photochemical smog.
Yet, the visibility reduction and odor resulting from smog are produced by other pollutants such as particulates and nitrogen oxides. Ozone is a secondary pollutant formed when nitrogen oxides and hydrocarbons react in the presence of sunlight. The reactivity of ozone causes health problems because it damages lung tissue, reduces lung function, and increases the sensitivity of the lungs to other irritants. Symptoms of decreased lung function include chest pain, coughing, sneezing and pulmonary congestion. Ozone can also act as an irritant to the mucous membranes of the eyes and throat and can reduce immune system capacity.