Characterisation of the carbonate content of atmospheric aerosols

A programme of aerosol sampling by dichotomous sampler has been undertaken with analysis of soluble ions plus carbonate. The technique for carbonate involved release of CO₂ by HCl vapour and quantitative measurement of the CO₂ by FTIR spectroscopy. The method is suitable for amounts down to below 10g CO₃^2- per filter. The prevailing atmospheric levels in an urban area were found to be below 1g m^-3. Information on the particle size from the dichotomous sampler was supplemented by use of a cascade impactor. Although CaCO₃ is clearly the dominant species initial analyses demonstrated higher carbonate levels than could be accounted for on the basis of the concentrations of calcium and magnesium ions which are the most likely cations in mineral carbonates. Analysis with and without heating to 100°C in a vacuum oven demonstrates the presence of carbonate in volatile form. This could be due to carbon dioxide adsorbed onto particulate matter such as soot.