Very short lived halocarbons (VSLH) play an important role in the transport of halogen atoms to the troposphere and lower stratosphere. Here we describe the development of a relaxed eddy accumulation system using gas chromatography coupled to a mass spectrometer (REA-GC/MS) to determine surface fluxes of VSLH with a time resolution of about 0.5 h. Laboratory tests showed that use of a common inlet for upward, downward and deadband flow paths resulted in mixing of upward and downward moving air masses, therefore we recommend the use of separate inlets. The modified system underwent field trials at Mace Head on the west coast of Ireland, where there are dense kelp beds known to emit a range of halocarbons. Over a 16 h period in mid-September 2007, the mean fluxes obtained were 16.1 +/- 1.8, 4.0 +/- 0.54 and 1.2 +/- 0.2 nmol m(-2) day(-1) for CH(2)Br(2), CH(2)ICl and CH(2)IBr, respectively. ; Times Cited: 4