Atmospheric Trends and Lifetime of CH ₃ CCI ₃ and Global OH Concentrations

Abstract

Determination of the atmospheric concentrations and lifetime of trichloroethane (CH(3)CCI(3)) is very important in the context of global change. This halocarbon is involved in depletion of ozone, and the hydroxyl radical (OH) concentrations determined from its lifetime provide estimates of the lifetimes of most other hydrogen-containing gases involved in the ozone layer and climate. Global measurements of trichloroethane indicate rising concentrations before and declining concentrations after late 1991. The lifetime of CH(3)CCI(3) in the total atmosphere is 4.8 +/- 0.3 years, which is substantially lower than previously estimated. The deduced hydroxyl radical concentration, which measures the atmosphere's oxidizing capability, shows little change from 1978 to 1994.

Atmospheric Methane: Trends and Impacts

“…Methane has an atmospheric lifetime of 8.9±0.6 based on analyses of methyl chloroform and good knowledge of the loss rate with OH (Prinn et al, 1995). This is lower than the previous estimate of 10 years (WMO, 1991(WMO, , 1995.…”

“…Observed trends in the seasonal cycle of methane, and global OH concentrations inferred from methylchloroform measurements do not support a significant change in OH over the past decades (Dlugokencky et al, 1997;Prinn et al, 1995). Similarly, modelling studies investigating the impact of observed stratospheric ozone depletion and temperature change over the past decade found that although the resulting increase in OH is compatible with the observed decrease in trend, by themselves they are insufficient to account for the entire decrease in growth rate (Bekki and Law, 1997;Fuglestvedt et al, 1994).…”

“…Most modelling studies conclude that OH concentrations have decreased by 10-30% since pre-industrial times, mainly due to increasing levels of CH 4 and CO in the atmosphere (e.g., Thompson, 1992). At the present time, OH concentration appears to be relatively steady, with the effects of increasing CH 4 and CO balanced by increases in tropospheric O 3 (Prinn et al, 1995;Krol et al, 1998). Although OH has no significant radiative effect, it is the primary oxidizing agent of the troposphere, responsible for the removal of not only methane, carbon monoxide, and NMHCs but numerous other pollutants as well.…”

“…However, most estimates of OH concentration have been obtained through measuring the concentration of a tracer molecule such as methylchloroform (CH 3 CCl 3 ) that can be used to infer the OH concentration with a chemical transport model. Using CH 3 CCl 3 data from 1978 to 1994 obtained at five ALE/GAGE stations around the globe, modelling studies deduced the average globally-integrated concentration of OH to be 9.7 x 10 5 (Prinn et al, 1995) and 1.07 x 10 6 molecules/cm 3 (Krol et al, 1998). Over the same time period, the studies by Prinn and Krol obtained a change in OH concentration of 0.0±0.2%/yr and 0.46±0.5%/yr, respectively.…”

Laboratory study on heterogeneous degradation of methyl chloroform (CH3CCl3) on aluminosilica clay minerals as its potential tropospheric sink

“…For most substances this information is insufficient enough to estimate this lifetime, with methyl chloroform (1,1,1-trichloroethane, CHaCC13) being the exception. That is, ground-level atmospheric concentrations of ca3cel 3 have been continuously measured worldwide since 1978 in Atmospheric Lifetime Experiment/Global Atmospheric Gases Experiment/Advanced Global Atmospheric Gases Experiment (ALE/GAGE/AGAGE) [Prinn et al, 1983b[Prinn et al, , 1992[Prinn et al, , 1995. AIF./GAGE/AGAGE is a major ground-based in situ network providing measurements of long-lived gases such as chlorofluorocarbons [Worm Meteorological Organization (WMO), 1998].…”