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Title:
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The role of aerosol/clouds in the radiation balance of theatmosphere: NOP project nr 852066
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Author(s):
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Published by:
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Publication date:
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ECN
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1995
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ECN report number:
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Document type:
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ECN-R--95-009
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Other
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Number of pages:
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Full text:
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38
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Download PDF
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Abstract:
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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