Radiative Effects and Halocarbon Global Warming Potentials of Replacement Compounds for Chlorofluorocarbons

Abstract

Instantaneous radiative forcing was calculated for 5 fluoroalcohols, 21 fluoroethers, and 5 fluoroamines which had been proposed as the replacement compounds for the currently used chlorofluorcarbons (CFCs) in refrigeration. Theatmospheric lifetimes of the compounds were also estimated from highest-occupied molecular orbital (HOMO) energy. Based on the radiative forcing and atmospheric lifetimes, halocarbon global warming 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 valid 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 absorption bands of a compound with those of ozone causes a significant cooling in the stratosphere, even if the compound does not exist in the stratosphere. 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 compounds should be taken into consideration as well as HGWP or GWP values when we assess the environmental effects due to replacement compounds. In this study, one parameter, defined as the ratio of the cooling rate at 30km and the tropopause, was proposed as a measure of the cooling in the stratosphere.
Spectral-resolution dependency of the calculated radiative effects was also studied. The results show that the resolution should be finer than about 50cm^-1 to calculate the radiative forcing and cooling rate precisely.