FULLY AUTOMATED GAS-CHROMATOGRAPH FLAME IONIZATION DETECTOR SYSTEM FOR THE IN-SITU DETERMINATION OF ATMOSPHERIC NONMETHANE HYDROCARBONS AT LOW PARTS-PER-TRILLION CONCENTRATION

A completely automated gas chromatography-flame ionization detector sy stem with cryogenic sample freeze-out for measuring atmospheric non-me thane hydrocarbons was deployed at the Mauna Loa Observatory, Hawaii d uring the MLOPEX II experiment, September 1991 through August 1992. Th e system was designed to (1) rapidly trap air samples of up to 4 litre s volume to allow for sub-parts per trillion detection limits, (2) eli minate interferences from ambient ozone, water vapor and carbon dioxid e, (3) reduce to negligible levels any contamination in the analytical systems, and (4) allow for continuous, unattended operation. The inst rumentation consisted of two parallel analytical systems, employing pa cked and capillary chromatographic columns, which allowed quantificati on of C-2-C-10 non-methane hydrocarbons from sub-parts per trillion to parts per million concentrations. A dynamic dilution system was used to calibrate the analytical system over the range of concentrations me asured (low parts per trillion to parts per billion) at this site.