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The role of aerosol/clouds in the radiation balance of theatmosphere: NOP project nr 852066
Gepubliceerd door: Publicatie datum:
ECN 1995
ECN publicatienummer: Publicatie type:
ECN-R--95-009 Overig
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38  Niet beschikbaar.

A cloud chamber was built to study the effect of anthropogenic originatedaerosol particles on cloud formation in The Netherlands. The results of the study provide maxima for the influence of manmade aerosol on the microstructure of clouds to be used in the calculation of their optical properties. The investigation of cloud formation in marine air is emphasized, since sensitivity studies show that the reflectivity of such clouds is most effectively influenced by the (extra) anthropogenic aerosol particles. For this reason the supersaturations in the study were as low as in typical marine stratus. The effect of the anthropogenic aerosols on cloud formation was determined from a comparison of the number of droplets formed in 'clean' arctic marine air versus the number of droplets formed in marine air which had traveled over the UK. The performance of the cloud chamber was tested with reference aerosol of varying number concentrations. It was found that the reference particles above a threshold ('critical') size of 0.07 micrometer grew into droplets. The number of cloud droplets formed in the clean marine air was 60 cm"-3, while the number of droplets formed in air masses which passed over the UK averaged 300 cm"-3. The polluted air masses were further divided into moderately and heavily polluted air. For the moderately polluted air on average about 50% of the aerosol particles of the proper size became droplets. This could be explained by the fact that only half of the particles are water-soluble and can serve as so-called cloud nuclei. In the heavily polluted air, with large numbers of aerosol particles, only a limited number of additional cloud droplets were formed. In continental air the number of cloud droplets was twice as much as those in the polluted marine air. This shows the limiting value for the number of droplets in 'polluted' continental clouds. It is strongly recommended to validate the results of the cloud chamber by aircraft campaigns in which the actual cloud droplet numbers in marine stratus are measured in the vicinity of the cloud chamber. 14 figs., 2 tabs., 3 appendices, 17 refs.

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