Evaluation of standards and methods for continuous measurements of carbon monoxide at ground-based sites in Asia

An international exercise to directly assess the consistency of standards and methods for measuring carbon monoxide (CO) was conducted as part of the East Asian Regional Experiment 2005 (EAREX 2005) in the framework of the Atmospheric Brown Clouds (ABC) project. Four groups representing Japan, Korea, Hong Kong, and Taiwan made comparisons at the Gosan super-site on Jeju Island, Korea, in March 2005, by setting up individual instruments with gas standards which are commonly used in ground-based monitoring programs in Asia. Intensive comparisons between two Japanese groups showed that a non-dispersive infrared absorption (NDIR) instrument agreed fairly well with a gas chromatograph / reduction gas detector (GC/RGD) with 1-h time resolution, confirming that NDIR methods are useful for monitoring, in particular, large temporal variations of CO in ambient air. Although international comparison of ambient measurements by NDIR indicated general agreement, comparison of gas standards revealed difficulties in preparing accurate and stable standard gases for monitoring CO at ambient levels.