Actually, higher concentrations of ozone is found above FL350 than on the surface. Airliners have ozone scrubbers to help alleviate ozone sickness. Airline companies issue ozone alerts to avoid pockets of high ozone concentrations.
Ozone is a variant of oxygen produced by the action of solar radiation on high altitude oxygen.
It is a toxic gas that damages the lungs by irreversibly destroying the elasticity of the lung tissue (emphysema).
Little ozone is present in the troposphere but concentrations rise rapidly above the tropopause increasing with altitude (greatest concentrations in winter and spring)
As the tropopause is much lower over the poles the risk from the effects of ozone is greatest on trans-polar flights.
Thus Ozone is a potential danger between 40,000 and 75,000 ft.
Symptoms of ozone poisoning are dryness of the nose and throat with irritation causing coughing and a discomfort in the chest.
Severe poisoning can cause breathing difficulties, heart strain and sometimes death.
Concentration of ozone is more significant than its exposure time.
FAA concentration limit is 0.25 parts per million by volume (ppmv) for commercial flights.
Ozone is partly destroyed by the high temperatures created in the compressors of jet engines.
Aircraft with lower compressor temperatures require catalytic converters and carbon filters to reduce the ozone concentration to an acceptable level.
Higher cabin humidity reduces the severity of the symptoms of ozone poisoning.
Ozone is usually destroyed by the pressurisation process.
