Atmospheric Methyl Chloride

Khalil, M.A.K., Department of Physics, Portland State University, Portland, Oregon; and R.A. Rasmussen, Department of Environmental Science and Engineering, Oregon Graduate Institute, Portland, Oregon

Prepared by Tom Boden, CDIAC

(2000) (http://cdiac.esd.ornl.gov/epubs/other/methylchl.html)

Monthly average concentrations of atmospheric methyl chloride from seven locations throughout the polar, middle, and tropical latitudes of both hemispheres are provided in this database. The seven primary sites include Pt. Barrow, Alaska; Cape Kumukahi and Mauna Loa, Hawaii; Cape Matatula, Samoa; Cape Grim, Tasmania; and the South Pole and Palmer Station, Antarctica. Concentration measurements from these seven sites cover a period of 16 years (1981-1997). Monthly data and vertical distributions at 20 short-term sites, from various latitudes, were also measured between 1987-1989.

Air samples were collected from various sites in stainless steel flasks and methyl chloride concentrations were measured using an Electron Capture Gas Chromatograph. Concentrations are reported as mixing ratios in dry air. The concentrations are determined by using a set of calibration standards that are referenced against a primary standard which is also used to establish the absolute concentration. The primary standards were prepared by the investigators in the absence of an available standard from a centralized location.