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Title:
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Activation properties of ambient aerosol in The Netherlands
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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-RX--95-045
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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 has been used to study the cloud-activation of ambientaerosol in The Netherlands. The large dimensions and throughput of the
chamber allowed unperturbed collection of aerosol and droplets with cascade
impactors and on-line measurements with cloud monitors (FSSP) inside the
facility. The study provided maxima for the number of man-made aerosol acting
as cloud nuclei. Emphasis was given to the investigation of cloud formation
in marine air, since sensitivity studies had shown that such clouds are most
effectively influenced by the (extra) anthropogenic aerosol particles. For
this reason the supersaturations in the study were low (on average 0.12%),
similar to those in actual marine stratus. The effect of the anthropogenic
aerosols on cloud formation was determined by comparing the number of
droplets formed in 'clean' arctic marine air to the number of droplets formed
in 'polluted' marine air (air which had travelled over the UK). Air masses
with the total aerosol number concentration in the order of 100 cm"-3 were
considered as 'clean' marine air. Air masses with higher aerosol
concentrations were divided into 'moderately' and 'heavily' polluted with
total aerosol concentrations in the order of 1,000 cm"-3 and 10,000 cm"-3,
respectively. In the clean marine air all potential cloud nuclei (particles
larger than the threshold size of the smallest reference particles that were
activated at a given supersaturation) were activated and the number of cloud
droplets formed was on average 45 cm"-3. In the moderately polluted air 72%
of potential cloud nuclei were activated and the average droplet number was
190 cm"-3. The difference in the actual cloud droplet number and the number
of potential cloud nuclei could be explained by the presence of
water-insoluble particles which do not activate. In the heavily polluted air
the average droplet concentration was around 320 cm"-3 which is on average
24% of the number of potential cloud nuclei. The heavily polluted case is of
less interest for the indirect effect since albedo of clouds 'saturates' at
high aerosol numbers. 9 figs., 4 tabs., 35 refs.
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