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Atmospheric Measurement Techniques An interactive open-access journal of the European Geosciences Union

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Atmos. Meas. Tech., 3, 39-50, 2010
© Author(s) 2010. This work is distributed under
the Creative Commons Attribution 3.0 License.
21 Jan 2010
Measurement of relative humidity dependent light scattering of aerosols
R. Fierz-Schmidhauser1, P. Zieger1, G. Wehrle1, A. Jefferson2, J. A. Ogren3, U. Baltensperger1, and E. Weingartner1 1Laboratory of Atmospheric Chemistry, Paul Scherrer Institut, Villigen, Switzerland
2CIRES, University of Colorado, Boulder, 80305, Colorado, USA
3National Oceanic and Atmospheric Administration (NOAA), Boulder, 80305, Colorado, USA
Abstract. Relative humidity (RH) influences the water content of aerosol particles and therefore has an important impact on the particles' ability to scatter visible light. The RH dependence of the particle light scattering coefficient (σsp is therefore an important measure for climate forcing calculations. We built a humidification system for a nephelometer which allows the measurement of σsp at a defined RH in the range of 40–90%. This RH conditioner consists of a humidifier followed by a dryer, which enables us to measure the hysteresis behavior of deliquescent aerosol particles.

In this paper we present the set-up of a new humidified nephelometer, a detailed characterization with well defined laboratory generated aerosols, and a first application in the field by comparing our instrument to another humidified nephelometer.

Monodisperse ammonium sulfate and sodium chloride particles were measured at four different dry particle sizes. Agreement between measurement and prediction based on Mie theory was found for both σsp and f(RH)=σsp(RH)/σsp(dry) within the range of uncertainty. The two humidified nephelometers measuring at a rural site in the Black Forest (Germany) often detected different f(RH), probably caused by the aerosol hysteresis behavior: when the aerosol was metastable, therefore was scattering more light, only one instrument detected the higher f(RH).

Citation: Fierz-Schmidhauser, R., Zieger, P., Wehrle, G., Jefferson, A., Ogren, J. A., Baltensperger, U., and Weingartner, E.: Measurement of relative humidity dependent light scattering of aerosols, Atmos. Meas. Tech., 3, 39-50,, 2010.
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