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 system with cryogenic sample freeze-out for measuring atmospheric non-methane hydrocarbons was deployed at the Mauna Loa Observatory, Hawaii during the MLOPEX II experiment, September 1991 through August 1992. The system was designed to (1) rapidly trap air samples of up to 4 litres volume to allow for sub-parts per trillion detection limits, (2) eliminate interferences from ambient ozone, water vapor and carbon dioxide, (3) reduce to negligible levels any contamination in the analytical systems, and (4) allow for continuous, unattended operation. The instrumentation consisted of two parallel analytical systems, employing packed and capillary chromatographic columns, which allowed quantification 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 measured (low parts per trillion to parts per billion) at this site.