Determination of inorganic and organic volatile acids, NH3, particulate SO 4 2− , NO 3 2− and Cl− in ambient air with an annular diffusion denuder system

Abstract

An annular denuder system for simultaneous determination of gaseous and particulate pollutants in ambient air was developed. Inorganic acids (HCl, HNO3) were collected in a NaF-coated denuder, while organic acids (HCOOH, CH3COOH) were trapped in one coated with KOH. NH3 was sampled with a H3PO4-coated denuder tube. Particulate H2SO4 was evaporated at elevated temperature (145°–155°C) and deposited on a NaF-coating together with HCl and HNO3 originating from thermal decomposition of NH4Cl and NH4NO3. NH3 resulting from deammoniation of (NH4)2SO4 as well as NH3 remaining from NH4Cl and NH4NO3 were collected in a H3PO4-coated denuder. The practical collection capacity of the tubes ranged from 0.35 to 1.0 μmol calculated from an experimentally determined sorption efficiency of at least 90%. The precision, expressed as relative standard deviation, of sampling and analytical procedures was determined from duplicate measurements in ambient air. The reproducibility varied from 9% to 14% for the gaseous components, while that of the particulate compounds ranged from 12% to 23%. Aqueous extracts of the denuder coatings were analysed for ionic components by ion chromatography using conductivity detection. The minimum detectable concentration in air was found to be 1.5 to 14 nmol/m3 for the different compounds calculated for 1.6 m3 sample volume, based on 3-h measurements at a flow of 9 l/min.