Evaluation of a two-and-a-half year study of acidic pollutants using Annular Denuder Systems

Abstract

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From October 1987 until april 1990 concentrations of the acidifying gases SO2, HNO2, HNO3, NH3 and particulate sulfate, nitrate, ammonium and hydronium were measured at three sites in the Netherlands, using Annular Denuder Systems. The locations, an urban, a suburban and a rural were situated from the northeast to the west of the country. Daily samples were taken, once in eight days at each location. During some smog episodes and periods corresponding with intensive epidemiological health studies, the sampling scheme was intensified at one or two locations. A fourth, urban site was included during the winter of 1989/1990. Additional field and laboratory experiments were performed to examine the precision and performance of the Annular Denuder System method. Validation procedures were developed in order to determine the reliability of the primary results and to eliminate results not satisfying certain criteria. Precision for the eight components varied between 2 and 15% and their accuracy between 5 and 25%. Detection limits were all low. The method showed rather good agreement with others. Disadvantages are the limited denuder capacity and hence limited measuring range for ammonia and the low time resolution (sampling must be done for at leat 3 and preferably 12 or 24 hours). Further, the method is time consuming and can hardly be automated. The study showed that average concentrations of H+ and HNO3 at the four sites were low (10nmol/m3) compared to values found in other countries, whereas for sulfate, nitrate and ammonium they were considerably larger, i.e. 100 to 200 nmol/m3. Elevated values were found for HNO3, sulfate, nitrate and ammonium during stable weather conditions. Ammonia concentrations at all sites were relatively large due to intensive lifestock breeding. The ammonia neutralizes acidifying aerosol and explains the low H+ values. Values for nitrous acid were rather large, probably as a result of the high traffic density in the Netherlands. Aerosol component concentrations at different sites were highly correlated, which can be explained from their stability and low deposition velocity.