RADIATIVE EFFECTS AND HALOCARBON GLOBAL WARMING POTENTIALS OF REPLACEMENT COMPOUNDS FOR CHLOROFLUOROCARBONS

Instantaneous radiative forcing was calculated for 5 fluoroalcohols, 2 1 fluoroethers, and 5 fluoroamines which had been proposed as the repl acement compounds for the currently used chlorofluorcarbons (CFCs) in refrigeration. Theatmospheric lifetimes of the compounds were also est imated from highest-occupied molecular orbital (HOMO) energy. Based on the radiative forcing and atmospheric lifetimes, halocarbon global wa rming potentials (HGWPs) were evaluated for the replacement compounds. Most of the HGWP values were smaller than 0.1 owing to their shorter lifetimes, and the results indicate that these compounds could be vali d candidates as replacements for currently used CFCs from the point of view of HGWP. The spectral cooling rate profiles were calculated for the replacement compounds in order to study the vertical structure of their radiative effects. It was found that overlapping of the absorpti on bands of a compound with those of ozone causes a significant coolin g in the stratosphere, even if the compound does not exist in the stra tosphere. This cooling does not directly relate to the HGWP value and the cooling rate profile in the troposphere. Therefore, it can be said that the vertical structure of the radiative effects caused by the co mpounds should be taken into consideration as well as HGWP or GWP valu es when we assess the environmental effects due to replacement compoun ds. In this study, one parameter, defined as the ratio of the cooling rate at 30 km and the tropopause, was proposed as a measure of the coo ling in the stratosphere. Spectral-resolution dependency of the calcul ated radiative effects was also studied. The results show that the res olution should be finer than about 50 cm(-1) to calculate the radiativ e forcing and cooling rate precisely.