Presentations and Publications

Khlystov, A., Zhang, Q., Jimenez, J.-L., Stanier, C., Pandis, S.N., Caragaratna, M.R., Fine, P., Misra, C., Sioutas, C., “In-situ concentration of semi-volatile aerosol using water-condensation technology”, Journal of Aerosol Science, Vol. 36(7), 2005, pp. 866-880.

The effect of concentratingsemi-v olatile aerosols usinga water-condensation echnology was investigated using the Versatile Aerosol Concentration Enrichment System (VACES) and the Aerodyne Aerosol Mass Spectrometer (AMS) duringmeasurements of ambient aerosol in Pittsburgh, PA. It was found that the shape of the sulfate mass-weighed size distribution was approximately preserved during passage through the concentrator for all the experiments performed, with a mass enhancement factor of about 10–20 dependingon the experiment. The size distributions of organics, ammonium and nitrate were preserved on a relatively clean day (sulfate concentration
around 7 microg/m^3), while duringmore polluted conditions the concentration of these compounds, especially nitrate, was increased at small sizes after passage through the concentrator. The amount of the extra material, however, is rather small in these experiments: between 2.4% and 7.5% of the final concentrated PM mass is due to “artifact” condensation. An analysis of thermodynamic processes in the concentrator indicates that the extra particle material detected can be explained by redistribution of gas-phase material to the aerosol phase in the concentrator. The analysis shows that the condensation of extra material is expected to be larger for water-soluble semi-volatile material, such as nitrate, which agrees with the observations. The analysis also shows that artifact formation of nitrate will be more pronounced in ammonia-limited conditions and virtually undetectable in ammonia-rich conditions.

 

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