There are two GML programs that measure CH3Cl. The longest and most complete measurement of CH3Cl is from the HATS flask GC-MSD program (data displayed below). The CATS in situ GCs also measure CH3Cl, however the data are less precise than the flask measurements.
Atmospheric dry mole fractions (parts-per-trillion or ppt) of CH3Cl measured by GC-MSD in the HATS flask program. Each point represents a monthly mean at one of 8-12 stations: Alert, Canada (ALT), Summit Greenland (SUM), Barrow, Alaska (BRW), Mace Head, Ireland (MHD), Trinidad Head, California (THD), Niwot Ridge, Colorado (NWR), Cape Kumukahi, Hawaii (KUM), Manua Loa, Hawaii (MLO), American Samoa (SMO), Cape Grim, Australia (CGO), Palmer Station, Antarctica (PSA), South Pole, Antarctica (SPO).
Zonal mean dry mole fractions (ppt) are estimated from the flask program by equally weighting monthly mean measurements in each latitude band. Small gaps (less than 6 months) are interpolated prior to averaging. Solid lines are used for Northern hemispheric measurements and dashed for the Southern hemisphere.