Ozone perturbations due to increases in N₂O, CH₄ and chlorocarbons: two-dimensional time-dependent calculations

Abstract

Time-dependent ozone perturbation estimates are performed in a 2-D diabatic circulation model with ozone photochemistry. Future increases in the emissions of N₂O, CH₄ and the chlorocarbons CFCl₃, CF₂Cl₂, CHClF₂, C₂Cl₃F₃, CH₃CCl₃ and CCl₄, are considered. The altitude variation of the calculated ozone change in the upper stratosphere is within the uncertainty limits of the observed trend reported from Umkehr data for the period 1970-1980, when the effect of temperature changes from CO₂ is included. Future ozone predictions consider only the photochemical response to source gai increases. For the integrations until the year 2030, four different emission scenarios for chlorine releases have been used. The average global ozone column has been reduced by 65% in the year 2030 compared to the 1960 level, when chlorine emissions are increased by 3%/year and the surface mixing ratio of N₂O and CH₄ by 0.25 and 10%/year, respectively. It should also be noted that in a case with low chlorocarbon emissions and a modest reduction in the total ozone column, the altitude profile is highly distorted. In addition, the latitude gradients are pronounced. When all the chlorocarbon emissions are stopped in the year 2000, a minimum in the total ozone column density is reached after about 5 years. The efficiency in the recovery of the ozone column is shown to be larger when CH₄ is assumed to increase, compared to a case when CH₄ is assumed to be constant. When the total chlorine approaches the amount of nitrogen in the stratosphere, ozone depletions begin to accelerate. This situation does not occur before the year 2030 in any of the model runs with the scenarios selected here. Ozone predictions were performed for an additional period of 50 years for the chlorocarbon scenario with the highest emissions. In this case, non-linear growth in ozone depletion was found after the middle of the next century.