ROUTINE, CONTINUOUS MEASUREMENT OF CARBON-MONOXIDE WITH PARTS-PER-BILLION PRECISION

A system including a commerical instrument (Thermo Electron Corp., Mod el 48) operating on the principle of gas filter correlation, nondisper sive infrared absorption is utilized to approach 1 ppbv precision with a 1-h averaging period in the measurement of slowly varying ambient C O levels in rural and remote regions. The instrument modifications, se tup, and signal averaging processes include gold-plated mirrors, selec ted detector, 1-s signal resonse time (all available as options from t he manufacturer), installation of a lens to more fully focus the infra red beam on the detector, standard addition calibration, catalytic zer oing, rapid switching between equal time periods in the measurement an d zero modes, and longterm averaging.