The effect on ozone depletion by supersonic transports is still a hotly debated issue. But most scientists accept that ozone depletion by nitrous oxides is caused by the following mechanisms in order of importance.
• Cruise altitude. For a given rate of N0^ injection into the atmosphere the rate of ozone depletion will go up nearly linearly with altitude from altitudes between 15 and 20 km.
• Combustor entry conditions. The higher the combustor entry temperature and pressure the higher the formation of N0^.
• Fuel Efficiency. The higher the fuel consumption the higher the formation of NOg.
Though the lower wing loading contributes to a higher cruise altitude, this effect is almost completely offset by the reduction in parasite drag. The reduced parasite drag will lead to a lower cmise lift coefficient and therefore a lower cruise altitude. Because the effect of fuel efficiency is less important than lowering the combustor entry conditions, the power plant effi* cicncy will be penalized by very strict ozone depletion standards After all elements were taken into account we did not find a significant difference in the ozone depiction of conventional wing-body aircraft and the oblique flying wing when the same cruise Mach number was considered. The effect OFW’s improved fuel efficiency was canceled by its somewhat increased flight altitude. According to the Chang model, the impact of a fleet of Mach 1.6 OFW’s replacing the current fleet of B747’s on the ozone layer will be less than the 2.5 reduction of the ozone column proposed by NASA. This is about one fourth of the impact of Mach 2.4 conventional transport and ten times the impact of the current subsonic fleet.