Characterization of particulate air pollution in urban and non-urban areas in the Netherlands.

During the winters of 1992/1993, 1993/1994 and 1994/1995 a monitoring study was performed in three urban and three non-urban areas in the Netherlands. PM10, black smoke (BS), sulfate, nitrate, ammonium (non-organic secondary aerosols, ''NOSA'') and aerosol acidity were measured on a daily basis in both the urban and non-urban areas. During the third winter, PM2.5 was measured as well. The elemental composition of PM10 was analyzed for one-third of the filters collected during the winter of 1993/1994 with inductively coupled plasma (ICP). PM10 and BS concentrations were on average 13% and 19% higher in the urban areas than in the non-urban areas. NOSA concentrations were on average 8% lower in the urban areas. PM2.5 concentrations were similar in the urban and non-urban area. Higher elemental concentrations in PM10 were found in the urban area for all elements except Si. The contrast between elemental concentrations in PM10 was for most elements larger than for PM10 mass concentration. The small contrast in particle concentrations between urban and non-urban areas in the Netherlands is probably a result of the small size of the country, the high population density, the lack of small-scale geographical and meteorological differences, and the importance of long-range transport of air pollutants. Both the absolute concentrations of PM10, BS and NOSA and the urban-non-urban differences depended strongly on wind direction. Easterly winds resulting in an influx of air masses from Central and Eastern Europe were associated with high concentrations and minimal urban-non-urban differences. Winds from the sea resulted in low concentrations but larger relative differences between urban and non-urban areas.