Concentrations of acidic air pollutants in The Netherlands

From October 1987 to April 1990 a monitoring study of atmospheric acidity has been performed at three urban and five rural sites in The Netherlands. Sampling was performed on a regular basis with annular denuder filter pack systems at all sites and a continuous sulfuric acid monitor at one site. Very high ammonia concentrations (mean concentration higher than 10 μg m−3) were observed at a site in an area with intensive livestock farms. The mean ammonia concentration at the urban sites was slightly higher than at the background sites. Despite the high ammonia concentrations the concentration of acid aerosol was not negligible. High concentrations of acid aerosol have not been observed, the highest daily average concentration, expressed as sulfuric acid, was 5.5 μg m−3. Daily average nitrous acid concentrations up to 20 μg m−3 have been observed, mostly at the more traffic influenced sites. Small spatial variability of the concentration of the aerosol components sulfate, nitrate and ammonium was found, consistent with the long-range transport behavior of these components. Larger spatial variability was observed for the gaseous components HONO, HNO3 and particularly ammonia, in agreement with the impact of local or regional sources.