Abstract. A two-dimensional model of sulfate aerosols has been developed. The model includes the sulfate precursor species H2S, CS2, DMS, OCS, and S02. Microphysical processes simulated are homogeneous nucleation, condensation and evaporation, coagulation, and sedimentation. Tropospheric aerosols are removed by washout processes and by surface deposition. We assume that all aerosols are strictly binary water-sulfuric acid solutions without solid cores. The main source of condensation nuclei for the stratosphere is new particle formation by homogeneous nucleation in the upper tropical troposphere. A signficant finding is that the stratospheric aerosol mass may be strongly influenced by deep convection in the troposphere. This process, which could transport gas-phase sulfate precursors into the upper troposphere and lead to elevated levels of S02 there, could potentially double the stratospheric aerosol mass relative to that due to OCS photooxidation alone. Our model is successful at reproducing the magnitude of stratospheric aerosol loading following the Mount Pinatubo eruption, but the calculated rate of decay of aerosols from the stratosphere is faster than that derived from observations.

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Model calculations using estimated reaction rates of sulfur hexafluoride (SF6) with OH and O(1D) indicate that the atmospheric lifetime due to these processes may be very long (25,000 years). An upper limit for the UV cross section would suggest a photolysis lifetime much longer than 1000 years. The possibility of other removal mechanisms are discussed. The estimated lifetimes are consistent with other estimated values based on recent laboratory measurements. There appears to be no known natural source of SF6. An estimate of the current production rate of SF6 is about 5 kt/yr. Based on historical emission rates, we calculated a present‐day atmospheric concentrations for SF6 of about 2.5 parts per trillion by volume (pptv) and compared the results with available atmospheric measurements. It is difficult to estimate the atmospheric lifetime of SF6 based on mass balance of the emission rate and observed abundance. There are large uncertainties concerning what portion of the SF6 is released to the atmosphere. Even if the emission rate were precisely known, it would be difficult to distinguish among lifetimes longer than 100 years since the current abundance of SF6 is due to emission in the past three decades. More information on the measured trends over the past decade and observed vertical and latitudinal distributions of SF6 in the lower stratosphere will help to narrow the uncertainty in the lifetime. Based on laboratory‐measured IR absorption cross section for SF6, we showed that SF6 is about 3 times more effective as a greenhouse gas compared to CFC 11 on a per molecule basis. However, its effect on atmospheric warming will be minimal because of its very small concentration. We estimated the future concentration of SF6 at 2010 to be 8 and 10 pptv based on two projected emission scenarios. The corresponding equilibrium warming of 0.0035°C and 0.0043°C is to be compared with the estimated warming due to CO2 increase of about 0.8°C in the same period.

In this paper we present the global distribution of TFA in the gas phase and in precipitation produced by the degradation of HFC-134a, HCFC-124, and HCFC-123 using a coarse grid chemical transport model (CTM), but including synoptic scale weather patterns, diurnal boundary layers, and wet and dry convective plume mixing processes derived from a general circulation model (GCM). Observed climatological values of 5747