Journal of Atmospheric Chemistry

, Volume 45, Issue 1, pp 79–99 | Cite as

Regional Sources of Methyl Chloride, Chloroform and Dichloromethane Identified from AGAGE Observations at Cape Grim, Tasmania, 1998–2000

  • M. L. Cox
  • G. A. Sturrock
  • P. J. Fraser
  • S. T. Siems
  • P. B. Krummel
  • S. O'Doherty


There are large uncertainties in identifying and quantifying the natural and anthropogenic sources of chloromethanes – methyl chloride (CH3Cl), chloroform (CHCl3) and dichloromethane (CH2Cl2), which are responsible for about 15% of the total chlorine in the stratosphere. We report two years of in situ observations of these species from the AGAGE (Advanced Global Atmospheric Gas Experiment) program at Cape Grim, Tasmania (41° S, 145° E). The average background levels of CH3Cl, CHCl3 and CH2Cl2 during 1998–2000 were 551± 8, 6.3± 0.2 and 8.9± 0.2 ppt (dry air mole fractions expressed in parts per 1012) respectively, with a two-year average amplitude of the seasonal cycles in background air of 25, 1.1 and 1.5 ppt respectively. The CH3Cl and CHCl3 records at Cape Grim show clear episodes of elevated mixing ratios up to 1300 ppt and 55 ppt respectively, which are highly correlated, suggesting common source(s). Trajectory analyses show that the sources of CH3Cl and CHCl3 that are responsible for these elevated observations are located in coastal-terrestrial and/or coastal-seawater regions in Tasmania and the south-eastern Australian mainland. Elevated levels of CH2Cl2 (up to 70 ppt above background) are associated mainly with emissions from the Melbourne/Port Phillip region, a large urban/industrial complex (population 3.5 million) 300 km north of Cape Grim.

chloromethanes methyl chloride chloroform dichloromethane Cape Grim Baseline Air Pollution Station baseline data annual cycle trajectory analysis pollution events coastal source regions 


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Copyright information

© Kluwer Academic Publishers 2003

Authors and Affiliations

  • M. L. Cox
    • 1
    • 2
  • G. A. Sturrock
    • 3
    • 4
  • P. J. Fraser
    • 3
  • S. T. Siems
    • 1
  • P. B. Krummel
    • 3
  • S. O'Doherty
    • 5
  1. 1.Department of Mathematics and StatisticsMonash UniversityClaytonAustralia
  2. 2.York UniversityNorth YorkCanada
  3. 3.CSIROAtmospheric ResearchAspendaleAustralia
  4. 4.University of East AngliaNorwichU.K
  5. 5.School of ChemistryUniversity of BristolBristolU.K

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