NORDIC INTERCOMPARISON FOR MEASUREMENT OF MAJOR ATMOSPHERIC NITROGEN SPECIES

A comparative study of measurements of atmospheric gaseous nitric acid and ammonia and particulate nitrate and ammonium concentrations was c onducted using various types of filter packs and denuder systems. Some of the filter packs used are recommended by the European Monitoring a nd Evaluation Programme (EMEP) and are widely used in the Nordic Count ries and elsewhere in Europe. In addition, nitrogen dioxide was measur ed using iodide-impregnated sintered glass filters and the differentia l optical absorption spectrometer method. Particulate nitrate and ammo nium concentrations were measured with two different size segregating samplers: a Berner low-pressure impactor and a virtual impactor. The w eather conditions were most of the time cool and humid. The agreement between different measurements was good for most species, but poor for gaseous ammonia. The Virtual impactor collected on average 17% more n itrate than the denuder systems, 24% more than filter packs and 37% mo re than the Berner low-pressure impactor. The nitrate discrepancy is b elieved to be due to inefficient coarse particle transport into the de nuder systems, fine particle nitrate evaporation in the filter packs a nd Berner low-pressure impactor and, to a lesser extent, possible coll ection of nitric acid by the virtual impactor. A substantial fraction of PM2.5 may be lost if the nitrate evaporation cannot be accounted fo r. The denuder systems did not collect particles larger than about 5.6 mu m equivalent aerodynamic diameter efficiently. Interferences were observed on the nitric acid measurements determined by a NaOH coated d enuder. NaCl coated denuders seemed to operate well in this study sinc e interferences were not observed. (C) 1998 Elsevier Science Ltd. All rights reserved.