Discussion in 'Chemistry' started by timojin, Dec 25, 2016.
How clean are the droplets in the clouds
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These days, the droplets (atmospheric moisture condensate) may not be too 'clean' - depending upon how chemically 'clean' the air is in which the droplets form and pass through during their journey to the earth's surface. Still, the droplets are likely cleaner than when they take residence on the earth's surface. Ozone likely does some 'cleaning' as does adsorption of CO2 (forms very slightly H2CO3/HCO acidic rainwater. Nastier air components/contaminants contribute to less-clean droplets.
Remember acid rain?
"Acid rain has eliminated insect life and some fish species, including the brook trout in some lakes, streams, and creeks in geographically sensitive areas, such as the Adirondack Mountains "
Do water remain in droplet form in the clouds because holds charge due to impurity ?
I'm not sure that impurities in 'droplets' play an important charge role - perhaps a meteorologist could chime-in here. IMO: Vertical air movements - warm vs cold - probably plays a more important charge role. Differential charges in/between cloud stratigraphies certainly plays an important role in lightening discharges and resultant thunder.
On the contrary, seeding clouds with impurities is a way to increase nucleation to get droplets to coalesce and fall as raindrops: https://en.wikipedia.org/wiki/Cloud_seeding
Would you not say , as you seed the material ( droplet ) you form larger aggregates and so the particle is converted into raindrop ? Or if the cloud particle is if a particular charge ( + or - ) with respect to the ground and is by seeding you neutralise the charge then the particles will coalesce and become larger and rain droplet wilform ?
True . . . . . but increased nucleation is due to 'particulate' surface interaction with free molecules (water) . . . not necessarily charge. [BTW: Same thing happens in magmas, nucleation begets increased nucleation.]
There does not seem to be any discussion in the link I provided about charged droplets.
Indeed. I was addressing the question of impurities rather than charge specifically. I suppose we should look up some articles about thunderclouds for a discussion of electric charge on cloud droplets and ice particles, but at the moment I can't be bothered - maybe later.
Most rain, and condensed airborne water generally, forms around some kind of particle of "non-air" stuff in the first place, and picks up more on its travels. Whether the word "impurity" is involved seems a semantic matter. Raindrops contain everything from dust to small arthropods - whatever one would see caught up in the surface layer of a small puddle. In my childhood, some individual thunderclouds rained fallout from open air bomb testing sufficient to injure grazing animals. Those clouds weren't very clean, in any reasonable sense.
Just to follow up on the query about electric charge and condensation, I've spent a few minutes looking for articles but can't find anything to support the idea that electric charge plays a well-defined role in droplet formation or coalescence. Most of the articles are about how charge separation occurs in bulk in clouds, leading to lightning etc. So it looks as if physical nuclei are what helps.
Perhaps a look at the work of Henrik Svensmark would be appropriate?
The idea is that cosmic rays seed clouds by ionizing molecules in Earth's atmosphere that draw in other molecules to create the aerosols around which water vapour can condense to form cloud droplets
I like that . because for some reason the clouds are o collection of droplets and without charge they should coalesse , but been charged with same charge they would repel, so there have to be some activity to remove the charge to coalesse
Yes I see; like a cloud chamber, in fact.
I had not come across Svensmark, but I've looked him up. It seems he is more or less on his own with this idea, though.
Cern was working on the same question.
I do not know their findings.
This is vicarious:
CLOUD also finds that ions from galactic cosmic rays strongly enhance the production rate of pure biogenic particles – by a factor 10-100 compared with particles without ions. This suggests that cosmic rays may have played a more important role in aerosol and cloud formation in pre-industrial times than in today’s polluted atmosphere.
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