Continuous Monitoring of Atmospheric HCl, HNO2, HNO3and SO2by Wet-Annular Denuder Air Sampling with On-Line Chromatographic Analysis

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Abstract
An automated system for the collection, in-line preconcentration and analysis of acidifying atmospheric gases is described. Collection of HCl, HNO2, HNO3 and SO2 from ambient air is carried out with an annular wet denuder. After addition of an internal standard to the sample flow and conductivity suppression, preconcentration of the sample flow is performed by pumping a measured volume of the sample flow through an anion exchange concentrator column. Following the concentration step, the anions of the corresponding acids are analyzed by ion chromatography with conductivity detection. The manifold described with two sample loops and two concentrator columns operating in parallel allows automated collection and analysis of two air samples per hour. A computer programme has been developed for automated performance. It allows the system to run unattendedly during extended periods as all the functions, including data processing, are computer-controlled. Factors affecting the performance are reported. The detection limits achieved are 5.4, 12 and 17 ng/m3 for HCl, HNO2, HNO3 and SO2 respectively, with relative standard deviations better than 4% at 1–2 μg/m3. Ambient measurements for Petten, The Netherlands, are presented which show the capability of the system for continuous monitoring of atmospheric acidifying gases.