Simultaneous collection of sulphur dioxide and sulphate by a selective sampler and their analysis at background levels

Abstract

Sulphate and sulphur dioxide (SO₂) were collected separately from the atmosphere, with high efficiency and selectivity, in a dual filter apparatus. The first filter, impregnated with perchloric acid, was used to collect the aerosol sulphate and the second filter, impregnated with sodium hydroxide solution, collected the gaseous SO₂. The analysis of these species was carried out by ion chromatography (sulphate) and voltammetry (SO₂) in the filter washings. Operating with sampling times of 30 min, at a filter face velocity of ca. 18 cm s^–1, the detection limits were estimated to be 0.8 µg m^–3 for sulphate and 0.3 µg m^–3 for SO₂. The possible oxidation of SO₂ by NO_x is discussed and the operating conditions required to make this reaction negligible are given.