Global carbon tetrachloride distributions obtained from the Atmospheric Chemistry Experiment (ACE)

N D C Allen,M P Chipperfield,G C Toon,D E Oram,C D Boone,D Fu,P F Bernath,G L Manney,D K Weisenstein

doi:10.5194/acp-9-7449-2009

Abstract

Abstract. The first study of the global atmospheric distribution of carbon tetrachloride (CCl4), as a function of altitude and latitude, was performed using solar occultation measurements obtained by the Atmospheric Chemistry Experiment (ACE) mission using Fourier transform spectroscopy. A total of 8703 profile measurements were taken in the upper troposphere and lower stratosphere between February 2004 and August 2007. The zonal distribution of carbon tetrachloride displays a slight hemispheric asymmetry and decreasing concentration with increasing altitude at all latitudes. Maximum carbon tetrachloride concentrations are situated below 10 km in altitude with VMR (Volume Mixing Ratio) values of 100–130 ppt (parts per trillion). The highest concentrations are located about the Equator and at mid-latitudes, particularly for latitudes in heavily industrialised regions (20–45° N), with values declining towards the poles. Global distributions obtained from ACE were compared with predictions from three chemistry transport models showing good agreement in terms of the vertical gradient despite an overall offset. The ACE dataset gives unique global and temporal coverage of carbon tetrachloride and its transport through the atmosphere. An estimated lifetime for carbon tetrachloride of 34±5 years was determined through correlation with CFC-11.

Highlights

The synthesis of carbon tetrachloride (CCl4, known as tetrachloromethane) from chloroform and chlorine was first reported by Regnault in 1839
Using the total stratospheric chlorine budget of 3.65 ppb derived by Nassar et al (2006) it is estimated from Atmospheric Chemistry Experiment (ACE) retrievals that carbon tetrachloride makes up approximately 3% of this value
The 2006 WMO report estimates that the surface concentration of carbon tetrachloride is declining at a rate of 1±0.1 ppt year−1

Summary

Introduction

The synthesis of carbon tetrachloride (CCl4, known as tetrachloromethane) from chloroform and chlorine was first reported by Regnault in 1839. Following concerns over the catalytic destruction of ozone by chlorine-containing species (Molina and Rowland, 1974) estimates of global emissions of carbon tetrachloride have been attempted (Galbally, 1976; Simmonds et al, 1988, 1998; Singh, 1976), poor industrial records and an underestimation of emissions in Asia (Palmer et al, 2003) and other parts of the world have led to significant levels of uncertainty. ATMOS (Atmospheric Trace MOlecule Spectroscopy) volume mixing ratio (VMR) profiles for carbon tetrachloride between 30◦ N and 51◦ N taken using a Fourier transform spectrometer (FTS) on the ATLAS-3 Space Shuttle Mission in November 1994 were compared with ER-2 aircraft data (Chang et al, 1996). To the best of our knowledge, there have been no prior reports of a global distribution of carbon tetrachloride using satellite data

Observations and retrievals

Results and discussion

Summary and conclusion