Field Intercomparison of Main Components in Air in EMEP

Within the European monitoring network (EMEP, http://www.emep.int) several different sampling procedures for measuring the main air components have been applied. This has contributed to systematic concentration differences and a comparability problem. Since 1997 co-located experiments in 15 countries have been carried out to quantify these differences. In addition, three major measurement campaigns were organized by EMEP between 1985 and 1991. Differences among results depend on the concentration level and methods used. The decrease in SO

2

concentrations over the last twenty years has placed greater demands on the methodology. Absorbing solutions methods for SO

2

, (H

2

O

2

and tetrachloromercurate (TCM)) typically have higher detection limits than the reference method, which uses KOH impregnated filters. The TCM method also has problems with negative interference, especially in summertime. UV fluorescence monitors have in a few cases proven to give good results, but interferences, detection limit and poor maintenance can be problems. For NO

2

, many countries are using the TGS absorption solution method, which has a higher detection limit than the reference method using NaI impregnated glass sinters.