WAECF

Two-Column Aerosol Project (TCAP): Winter Aerosol Effects on Cloud Formation

4 February 2013 - 28 February 2013

Lead Scientist: Daniel Cziczo

Observatory: AMF, PVC

The formation of clouds is an essential element in understanding the Earth’s radiative budget. Liquid water clouds form when the relative humidity exceeds saturation and condensed-phase water nucleates on atmospheric particulate matter. The effect of aerosol properties such as size, morphology and composition on cloud droplet formation has been studied theoretically as well as in the laboratory and field. Almost without exception these studies have been limited to parallel measurements of aerosol properties and cloud formation or collection of material after the cloud has formed at which point nucleation information has been lost. Studies of this sort are adequate when a large fraction of the aerosol activates but correlations and resulting model parameterizations are much more uncertain at lower supersaturations and activated fractions. The objective of this study was to determine the effect of aerosol properties on cloud droplet formation in situ and in real time. To accomplish this we combined a CCN chamber with a pumped counterflow virtual impactor (PCVI) to separate droplets formed as a function of saturation and temperature from the un-activated aerosol in our laboratory. The composition of the droplet-forming aerosol was then determined with an Aerosol Mass Spectrometer (AMS; Aerodyne Research, Inc., Billerica, MA) and/or a single particle mass spectrometer.