Publication Type:Journal Article
Source:Journal of Geophysical Research: Atmospheres, Volume 91, Issue D3, p.3985 - 4001 (1986)
Keywords:Middle atmosphere: composition and chemistry, Troposphere: composition and chemistry
An efficient three-dimensional spectral model is used to investigate the tropospheric and stratospheric circulation, chemistry, and photochemistry of the long-lived atmospheric species CFCl3, CF2Cl2, CH3CCl3, CCl4, and N2O. The model uses precalculated three-dimensional spectral fields of vorticity, vertical velocity, temperature, and ozone concentration and current estimates of the magnitudes and distributions of industrial and natural sources of the various species. Explicit calculations of instantaneous photodissociation rates for each species are carried out, and reactions with atmospheric OH and O(1D) and dissolution in the ocean are also included in the model where relevant. Available measurements of the horizontal, vertical, and temporal distribution of the modeled atmospheric species generally compare favorably with our calculations. However, there are some disagreements, particularly between the observed and calculated surface distributions of CH3CCl3 and the vertical distributions of CCl4, which are critically discussed. Assuming that their destruction is dominated by photodissociation and reaction with O(1D), the calculated present-day global atmospheric lifetimes of CFCl3, CF2Cl2, CCl4, and N2O are 73, 210, 48, and 182 years, respectively. Decreasing the O2 absorption cross sections in the Schumann-Runge continuum (2000–2200 Å) by 40% results in a decrease of the CFCl3 lifetime to 44 years. The calculated atmospheric lifetime of CH3CCl3 due to photodissociation and reaction with OH and O(1D) is 12 years, but this result depends on the prescribed seasonally dependent zonally invariant OH distribution used in the model.