MEASUREMENT OF ATMOSPHERIC NITRIC-ACID IN GAS-PHASE AND NITRATE IN PARTICULATE MATTER BY MEANS OF ANNULAR DENUDERS

A denuder technique for the determination of nitric acid and particula te nitrate is described. The technique relies on the use of four annul ar denuders set in series followed by a downstream filter-pack, and al lows die reliable and accurate measurement of gaseous nitric acid, coa rse nitrate and fine nitrate, even in the presence of high concentrati on levels of other nitrogen gaseous species and in case of high partic ulate to gaseous phase ratio. Field data collected by using the descri bed system in extreme conditions, ranging from very polluted areas to extremely remote sites, are discussed. The data are analyzed in terms of mass distribution of the analyte on the different stages of the set -up; time resolution, minimum detectable concentration and precision o f the measurements are also discussed.