Particle size and chemical composition of urban aerosols

The size distribution of airborne particulates (PM10) has been measured by using Andersen Mark II cascade impactors. The measurements were done at four sites, three of which were in the Leeds area, including one roadside site and the fourth at a rural site. On average 10–20% of the mass of urban PM10 particles were found to be below 0.43 μm and 50% below l.5 μm. Extracted samples were analysed for sulphate, nitrate and chloride using ion chromatography, ion selective electrode to determine ammonium and Gran's titration to determine acidity. The results show that both sulphate and nitrate peak on the 1.1-μm stage. Nitrate is spread over both coarse and fine modes and is depleted in the finest particles 2.1 μm relative to sulphate. The chloride levels, dominated as they are by sea salt chloride, show a much coarser distribution with