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ECN publication
A high-flow humidograph for testing the water uptake by ambient aerosol
Published by: Publication date:
ECN 1-10-1999
ECN report number: Document type:
ECN-RX--99-036 Article (scientific)
Number of pages:

Published in: Submitted for publication in Atmospheric Environment (), , , Vol., p.-.

A scanning humidograph, with an air flow rate of 0.5 m3 s"-"1 was builtto investigate the uptake of water and its effect on sizing, collection and light-scattering of ambient aerosol. The performance of the system was assessed with laboratory particles of ammonium nitrate, ammonium sulfate and sodium chloride which are the major hygroscopic components of ambient aerosol. The increase in size at the deliquescence points, which ideally is a stepwise function of relative humidity, occurs over a range of 3% RH units. This is shown to be an optimum value in a system of such large dimensions. Because of the strong temperature increase of the vapor pressure of ammonium nitrate, its evaporative loss was investigated as a function of heating/drying temperature. The loss of pure test aerosol, with a mass distribution similar to that in the ambient atmosphere, was found to be acceptable for drying temperatures of up to 40C. The sizing of deliquesced aerosol by LAS-X monitors was tested and found to be a complex function of RH. In Berner low pressure impactors growth of hygroscopic aerosol was not observed, not even at an RH approaching saturation. 21 refs.

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