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 particulate nitrate is described. The technique relies on the use of four annular denuders set in series followed by a downstream filter-pack, and allows die reliable and accurate measurement of gaseous nitric acid, coarse nitrate and fine nitrate, even in the presence of high concentration levels of other nitrogen gaseous species and in case of high particulate to gaseous phase ratio. Field data collected by using the described 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 of the measurements are also discussed.