Development of an automated, simultaneous and continuous measurement system by using a diffusion scrubber coupled to ion chromatography for monitoring trace acidic and basic gases (HCl, HNO3, SO2 and NH3) in the atmosphere

Abstract

An automated simultaneous measurement system for monitoring acidic and basic gases such as HCl, HNO3, SO2 and NH3 in the atmosphere was developed by using a diffusion scrubber coupled to an ion chromatograph (DS-IC system). Acidic and basic gases were effectively collected by the diffusion scrubber which consisted of a hydrophobic porous polytetrafluoroethylene (PTFE) tube disposed concentrically within a Pyrex-glass tube. De-ionized water was used as a scrubbing solution for collecting the acidic and basic gases such as HCl, HNO3, SO2 and NH3, which were dissociated to ion species (Cl–, NO3–, SO32–, SO42– and NH4+, respectively). After the collection of gases, the total anions and cations in the scrubbing solution were preconcentrated in anion and cation concentrator columns connected in series. All the analyte ions were separated and determined by ion chromatography. All operations relating to the air sampling, the preconcentration and the ion chromatographic analysis were controlled by a sequencer. Automated simultaneous continuous measurement could be performed at 60 min intervals. The collection efficiencies of the acidic and basic gases were higher than 97% at an air flow rate of 1 l min–1. The detection limits (3ς of the blank value) of HCl, HNO3, SO2 and NH3 were less than 0.01 ppbv for a 52 l of air sampling volume. The interference from co-existing NO2 for measuring HNO3 was negligible. The concentrations of SO2 measured by this automated measurement (DS-IC) system showed good agreement with those obtained with a pulse-fluorescence meter.