Estimating tropospheric lifetimes and ozone-depletion potentials of one- and two-carbon hydrofluorocarbons and hydrochlorofluorocarbons

Abstract

Tropospheric lifetimes and ozone-depletion potentials (ODPs) are estimated for all 53 possible one-and twocarbon hydrofluorocarbons (HFCs) and hydrochlorofluorocarbons (HCFCs). The relationships among C-H bond strength, activation energy for removal of H by OH, tropospheric lifetime, and ODP are examined. Algorithms are developed that are easy to apply and accurate enough for initial screening purposes. On the basis of extant theory and our analysis, the controlling variables for determining HCFC tropospheric lifetimes include number of hydrogen atoms, molecular weight, number of carbons, number of chlorine atoms a and ß to hydrogen, and number of fluorine atoms ß to hydrogen. The formula presented predicts lifetimes for molecules with atmospheric lifetimes below 30 years with a root mean square (rms) error of a factor of 2.4. An algorithm is also presented to calculate ODP based on tropospheric lifetime; the overall rms error for calculating ODP from the structure is a factor of 2.5. In many cases, ODPs of chlorine-containing compounds are predicted to be below 0.001. These estimates also aid in making tentative choices among alternative HFCs and HCFCs based on environmental considerations.

IMPACT OF CFCs ON OZONE LAYER AND GLOBAL WARMING

“…ts is the transport time from the surface of the earth up to the lower part of the stratosphere. t is the time as integration variable T is the length of the period of time over which the ozone depletion is quantified, and are the respective atmospheric lifetimes of substance (i) and CFC11, defined as the time elapsed before the quantity is reduced to i/e=37% of the quantity emitted (Nimitz and Skaggs, 1992). The lifetime corresponds to 1.41 times the half-life.…”

Stability of trifluoromethane in forest soils and methanotrophic cultures

“…Although the various HFCs and HCFCs have low ODPs, they generally have a significant global warming potential [5]. The global warming potential (GWP) for radiatively active trace gases is a function of their characteristic absorption of infrared radiation and atmospheric concentrations and lifetimes [1, 6–9]. For a number of the CFC substitutes, GWPs have been assumed to be limited in part by their relatively short atmospheric residence times, and the short residence times of their degradation products [1, 5].…”

Reactive Chlorine Compounds in the Atmosphere

“…The GWPs are from WMO (1995, chap 13) and IPCC (1995, part I, chap 5). The ODPs for COCl 2 , CHCl 3 , C 2 HCl 3 , and C 2 Cl 4 are from Kindler et al (1995), for CH 2 Cl 2 from Nimitz and Skaggs (1992), and for the rest of the gases from WMO (1995, chap 13), using the semi-empirical ODPs when available and modelderived values otherwise.…”