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

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^-, SO₃^2-, SO₄^2- 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.