The GASS-35 gas conditioning system has been designed to meet the needs of regulators and stack gas test agencies for ultra-low CEMS verification and inspection. It utilizes the unique properties of Nafion polymer to remove moisture from the sample gas, enabling accurate analysis of low SO2 in high humidity samples without requiring purge gas. The sample gas flowrate can reach 2.0 LPM and dew point after conditioning can be lower than 0°C, which prevents the dissolving loss of low-concentration SO2 during condensation and dehydration. This level of performance ensures measurement stability and accuracy with portable analysers, including popular infrared and electrochemical models.