Hydrosols and Microbubbles: Evaporation Suppression, Water Conservation, and Global Cooling

 What's this? Another evaporation suppression post already? Yes, but it's different from the usual floating covers, alcohol monolayers, and the like. Real different. So different that I need to go through a little geoengineering to get there.

Several months ago Russell Seitz, a Fellow of of the Department of Physics at Harvard University, sent me a paper that had been published in the journal Climatic Change [DOI 10.1007/s10584-010-9965-8] in December 2010. It was titled, Bright water: hydrosols, water conservation and climate change, and he asked me to comment on its applicability. It took me awhile to get around to it.

Here is his very informative Power Point PDF (updated 19 July 2012): 

Download The_Bright_Water_slideshow

And here are the paper and abstract:

 Download Climatic Change Article Springer

Abstract Because air–water and water–air interfaces are equally refractive, cloud droplets and microbubbles dispersed in bodies of water reflect sunlight in much the same way. The lifetime of sunlight reflecting microbubbles, and hence the scale on which they may be applied, depends on Stokes Law and the influence of ambient or added surfactants. Small bubbles backscatter light more efficiently than large ones, opening the possibility of using highly dilute micron-radiu hydrosols to substantially brighten surface waters. Such microbubbles can noticeably increase water surface reflectivity, even at volume fractions of parts per million and such loadings can be created at an energy cost as low as J per m**2 to initiate and mW per m**2 to sustain.  Increasing water albedo in this way can reduce solar energy absorption by as much as 100 W per m**2, potentially reducing equlibrium temperatures of standing water bodies by several Kelvins. While aerosols injected into the stratosphere tend to alter climate globally, hydrosols can be used to modulate surface albedo, locally and reversibly, without risk of degrading the ozone layer or altering the color of the sky. The low energy cost of microbubbles suiggests a new approach to solar radiation management in water conservation and geoengineering. Don't dim the sun; brighten the water.

 

Seitz is a big thinker and spends much of the paper discussing the use of microbubbles to increase the reflectivity of the oceans so that more solar radiation is reflected. He runs a simulation using a GCM to show that water body temeratures could be reduced by a few degrees Kelvin.

He's no Pollyanna and realizes that more study must be done before such a scheme could be implemented. And what about the cost? But he posits how current ship traffic could be used to produce and distribute the microbubbles. And he notes that it would likely have fewer adverse impacts than putting aerosols into the atmosphere, and could be easily 'turned off' if something started to go awry.  

While the global cooling aspect intrigued me, it was the evaporation suppression in freshwater bodies that piqued my hydrological curiosity.

Seitz admitted in an email that he is far more interested in the water conservation aspects. Amen!

He talks about cooling ponds, farm ponds, and reservoirs. An example is provided where a farmer could annually save about a million gallons (3 acre-feet) from a 1 hectare (2.47 acres) pond if she could lower the evaporation rate by just 1 mm/day.   

But what about applying this concept to huge reservoirs such as Lake Mead and Lake Powell? The former annually loses about 800,000 acre-feet to evaporation; the latter, more like 600,000 acre-feet.

Now that's real water! Imagine how happy Pat Mulroy would be if she could get her hands on an extra 50,000 - 100,00 acre-feet or so. Imagine how much that would cost. Probably cheaper and less acrimonious than a pipeline.

Regarding cost, Seitz sent me this email:

The extant microbubble generators are rediculously inefficient compared to the actual energy cost of inflating the bubbles - there is about two orders of magnitude of room for improvement, but somebody must be motivated to pay for engineering development - it's about where aircraft engines were in 1911.

If we can think about using microbubbles in oceans why not consider applying them to reduce evaporation in large terrestrial freshwater bodies? Certainly worth a study.

Keep in mind that others, notably Ray Walker,  have proposed obtaining an additional 1 MAF or so per year of unallocated water from the Colorado River system before. Walker never divulged to me the source of that water, but I suspect it was from evaporation suppression, perhaps by covers (see yesterday''s post) or a monolayer of alcohol. As far as I know no one ever took him on his offer. But Seitz's scheme should generate interest. 

 Here is another opinion of Seitz's concept.

As academics are wont to say, further research is indicated. Let's hope so. 

"Happiness is like a cloud, if you stare at it long enough, it evaporates." -- Sarah McLachlan

Comments

[Jerry Toman]

I don't know if aerosols will suppress evaporation in arid climates, but in areas where there is plenty of water and that water is too warm (90 F)--too warm to use as coolant for a nuclear power plant, you could cool it by creating an artificial waterspout on the shores of the river.

On a pond created adjacent to the river, or by using pumps, the Atmospheric Vortex Engine could be used to cool surface waters, while creating renewable power.

About 10-15 F of cooling could be expected, depending on the WBT (dewpoint) of the ambient air.

http://vortexengine.ca

[Paul Harms]

I have heard of the opposite - increasing evaporation by using a blue dye to make the water darker. http://www.intrepidpotash.com/loc/moab.html