Regional sources of methyl chloride, chloroform and dichloromethane identified from AGAGE observations at Cape Grim, Tasmania, 1998-2000

ML Cox*, GA Sturrock, PJ Fraser, ST Siems, PB Krummel, S O'Doherty

*Corresponding author for this work

Research output: Contribution to journalArticle (Academic Journal)peer-review

41 Citations (Scopus)

Abstract

There are large uncertainties in identifying and quantifying the natural and anthropogenic sources of chloromethanes-methyl chloride (CH(3)Cl), chloroform (CHCl(3)) and dichloromethane (CH(2)Cl(2)), 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 (41degreesS, 145degreesE). The average background levels of CH(3)Cl, CHCl(3) and CH(2)Cl(2) during 1998-2000 were 551+/-8, 6.3+/-0.2 and 8.9+/-0.2 ppt (dry air mole fractions expressed in parts per 10(12)) respectively, with a two-year average amplitude of the seasonal cycles in background air of 25, 1.1 and 1.5 ppt respectively. The CH(3)Cl and CHCl(3) 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 CH(3)Cl and CHCl(3) 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 CH(2)Cl(2) (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.

Original languageEnglish
Pages (from-to)79-99
Number of pages21
JournalJournal of Atmospheric Chemistry
Volume45
Issue number1
Publication statusPublished - May 2003

Keywords

  • chloromethanes
  • methyl chloride
  • chloroform
  • dichloromethane
  • Cape Grim Baseline Air Pollution Station
  • baseline data
  • annual cycle
  • trajectory analysis
  • pollution events
  • coastal source regions
  • HALOGENATED ORGANIC-COMPOUNDS
  • SPRUCE FOREST SOIL
  • EMISSIONS INVENTORY
  • REACTIVE CHLORINE
  • TRICHLOROMETHANE CHLOROFORM
  • GLOBAL EMISSIONS
  • CARBON-DIOXIDE
  • ATMOSPHERE
  • ATLANTIC
  • BIOSYNTHESIS

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