Another thought is if you are making micro bubbles you presumably will be
injecting air into water which will hasten air/sea CO2 equilibration and hence
(in ocean areas undersaturated in CO2 relative to air) speed up air CO2
absorption by the ocean, great for air CO2, bad for ocean acidification.
[Conversely, aerating upwelling areas will hasten ocean--> air CO2 transfer,
bad for air, good for acidity?] Also, won't you super saturate the water with
O2 and N2, suppressing photosynthesis and impacting animal physiology e.g.
http://www.ecy.wa.gov/programs/wq/tmdl/ColumbiaRvr/062308mtg/TDGeffectsLitRev080615.pdf
?
Greg
From: Klaus Lackner <[email protected]>
To: "[email protected]" <[email protected]>;
"[email protected]" <[email protected]>; geoengineering
<[email protected]>
Sent: Monday, April 3, 2017 10:09 AM
Subject: Re: [geo] Low intensity geoengineering – microbubbles and microspheres
#yiv5013475219 #yiv5013475219 -- _filtered #yiv5013475219 {panose-1:2 4 5 3 5 4
6 3 2 4;} _filtered #yiv5013475219 {font-family:Calibri;panose-1:2 15 5 2 2 2 4
3 2 4;} _filtered #yiv5013475219 {panose-1:2 0 5 3 0 0 0 2 0 4;}#yiv5013475219
#yiv5013475219 p.yiv5013475219MsoNormal, #yiv5013475219
li.yiv5013475219MsoNormal, #yiv5013475219 div.yiv5013475219MsoNormal
{margin:0in;margin-bottom:.0001pt;font-size:12.0pt;}#yiv5013475219 h1
{margin-right:0in;margin-left:0in;font-size:24.0pt;font-weight:bold;}#yiv5013475219
h2
{margin-right:0in;margin-left:0in;font-size:18.0pt;font-weight:bold;}#yiv5013475219
h3
{margin-right:0in;margin-left:0in;font-size:13.5pt;font-weight:bold;}#yiv5013475219
a:link, #yiv5013475219 span.yiv5013475219MsoHyperlink
{color:blue;text-decoration:underline;}#yiv5013475219 a:visited, #yiv5013475219
span.yiv5013475219MsoHyperlinkFollowed
{color:purple;text-decoration:underline;}#yiv5013475219 p
{margin-right:0in;margin-left:0in;font-size:12.0pt;}#yiv5013475219
span.yiv5013475219Heading1Char {color:#2F5496;}#yiv5013475219
span.yiv5013475219Heading2Char {color:#2F5496;}#yiv5013475219
span.yiv5013475219Heading3Char {color:#1F3763;}#yiv5013475219
span.yiv5013475219money {}#yiv5013475219 span.yiv5013475219EmailStyle24
{font-family:Calibri;color:windowtext;}#yiv5013475219 span.yiv5013475219msoIns
{text-decoration:underline;color:teal;}#yiv5013475219
.yiv5013475219MsoChpDefault {font-size:10.0pt;} _filtered #yiv5013475219
{margin:1.0in 1.0in 1.0in 1.0in;}#yiv5013475219 div.yiv5013475219WordSection1
{}#yiv5013475219 Quite likely it is even more complicated. The bubbles return
light to the surface, but this could cause a surface layer to see more intense
light than normally. (Rather than vanishing at depth, light that makes it
through the first thin layer, returns from below and passes through the same
layer a second time. So it is darker a few feet down and brighter higher up.
How this affects the eco-system is anybody’s guess. The problem with many of
these options is that they locally look just fine. They only have impact
because they operate on a large scale. But they typically will have more
impacts than just the one which is desired. From:
<[email protected]> on behalf of Franz Dietrich Oeste
<[email protected]>
Reply-To: "[email protected]" <[email protected]>
Date: Monday, April 3, 2017 at 7:04 AM
To: "[email protected]" <[email protected]>, geoengineering
<[email protected]>
Subject: Re: [geo] Low intensity geoengineering – microbubbles and microspheres
Dear All, Microbubbles and microspheres to brighten the oceans surfaces -
brilliant idea? My answer is No. This idea will not work because the bubbles
reflect sunlight. Just this sunlight phytoplankton needs to fix CO2 by
assimilation. What is the consequence of this? At least a faster increase of
the CO2 concentration in the atmosphere. Additional severe consequences to the
oceanic ecosystems. For instance: because phytoplankton is the basis of the
oceanic food chain any reduction of phytoplankton mass will have negative
consequences on the oceanic food web; coral reefs might die away because they
need sunlight to live. All best, Franz ------ Originalnachricht ------
Von: "Andrew Lockley" <[email protected]> An: "geoengineering"
<[email protected]> Gesendet: 03.04.2017 15:03:46 Betreff: [geo]
Low intensity geoengineering – microbubbles and microspheres
Old but brilliant - A
https://www.google.com.au/amp/s/bravenewclimate.com/2011/10/08/low-intensity-geoengineering-microbubbles-and-microspheres/amp/
Low intensity geoengineering – microbubbles and microspheres
Barry Brook 5 years ago Guest post by John Morgan. John runs R&D programmes
at a Sydney startup company. He has a PhD in physical chemistry, and research
experience in chemical engineering in the US and at CSIRO. He is a regular
commenter on BNC. A 9-page printable PDF version of this post can be downloaded
here. ———————————–
Crazy talk
Geoengineering is crazy. The sheer scale of the aspiration speaks of hubris.
Terraforming the planet by pulling down billions of tonnes of carbon dioxide,
or pushing millions of tonnes of plastic up into orbit is absurd. The material
intensities and costs are ridiculous. And yet, with no deep cuts in emissions
in evidence, with atmospheric CO2 at 390 parts per million and climbing at a
rate of about 2 ppm a year, our “safe” working level of 350 ppm is rapidly
disappearing in the rear view mirror even as we’re pushing the pedal harder to
the floor. We do a lot of crazy things. But what if there was a geoengineering
approach that used no materials, almost no energy, works at sea level, with
cheap technology we could start deploying at scale today? That’s exactly what
Russell Seitz at Harvard is proposing. In this post I want to look at his idea
of increasing the reflectivity of the oceans with tiny microbubbles, It’s a
fascinating, low impact concept, though not without some challenges. So I’ll
also propose a different means to the same end that addresses these issues, and
of course has some of its own. Then we can talk about how crazy it all is.
Bright Water
In a remarkable paper published just over a year ago – which I highly
recommend reading – Seitz proposed injecting microbubbles of air into seawater,
effectively creating an “inverse cloud”. Sunlight is scattered back into space
from these bubbles. This concept has no material inputs, bubble sparging
equipment is cheap and low power, and could be installed on ships already
travelling the worlds waterways. We don’t need to launch giant lenses into
space or build giant balloon tethered pipelines to the stratosphere. We have a
much more down to earth delivery system already in place, in the form of more
than 10 000 ships at sea, 1300 working oil rigs and many thousands of retired
platforms (3500 in the Gulf of Mexico alone) not to mention islands and
suitable coastlines.
It’s the little bubbles of nothing that make it really something
The appeal of this technique comes from the fact that you only need very small
bubbles to scatter light. Leveraging the cube law relationship for volume gives
you a lot of scattering power if you can make really small bubbles. The air
from a single 1 cm bubble, could fill a trillion 1 μm bubbles. Seawater
naturally contains up to 1 ppm by volume of air as larger bubbles – in the
10-100 μm range. Their reflectance can be measured, but is so small as to be
irrelevant to the Earth’s energy balance. But if this quantity of air were
broken down to 1 μm bubbles, there would be a million more of them, and Seitz
estimates the backscattered light would amount to several watts per square
metre. That’s some serious power. Light scattering from small spherical
particles is calculated using Mie theory, a fairly horrendous piece of
mathematical machinery. Seitz reports Mie theory scattering results 1 μm radius
bubbles at various concentrations. At 0.2 ppm of air in water as 1 μm radius
bubbles, the albedo (reflectivity) increase is 1%, equal to the current CO2
forcing (Figure 2). This is an astonishing result: global warming is fully
offset by 0.2 parts per million of 1 μm bubbles! Using the IPCC mid-range
climate sensitivity of 0.7 K per Wm-2 the global average temperature would
decrease by about 1 degree, more than the 0.74 K warming seen in the 20th
century. The NCAR CAM3.1 climate model was used to look at the effect of 1 ppm
of 1 μm bubbles in a 780 ppm CO2 scenario – double our current CO2 level. Under
this extravagant CO22 burden the model nevertheless indicated a cooling of 2.7
K [Seitz 2010; Figure 5]. So microbubbles really could be a powerful engineered
response to climate change, if we can deploy them.
Not so fast
But won’t these bubbles just bubble up to the surface and burst? Not the small
ones, it turns out. The velocity of a rising bubble is readily calculated (from
the Stokes equation), and a one micron radius bubble takes about 5 days to rise
a metre. With near-surface mixing they’ll be there for a while. No, the real
problem is that the bubbles want to dissolve. The air inside a bubble is at a
higher pressure than the water it floats in, because surface tension is trying
to pull the surface inwards, and the air is compressed. The pressure increase
(given by the Young-LaPlace equation) is greater the smaller the bubble, and
can be surprisingly large. For a 1 mm diameter bubble in seawater, the internal
pressure is almost 3 atmospheres greater than the water outside. At these high
pressures the air bubble will rapidly dissolve, even in water that is saturated
with air at sea level. Unstabilized 10 μm bubbles in seawater are observed to
dissolve in about 10 seconds. However, as Seitz describes, some seawater
bubbles are much more durable, being stabilized by adsorption of natural
surfactants and small particles on their surfaces. These materials form
incompressible surface films that balance the pull of surface tension, and
stabilized bubbles in the micron size range have been observed to last for
20-30 hours. So the key to the bright water concept is increasing the lifetime
of these bubbles by ensuring that they are stabilized somehow. I’ll discuss
some possible strategies for this below.
I’m forever blowing bubbles
– Doris Day, On Moonlight Bay Another problem is generation of microbubbles.
Making large bubbles is easy. Making small bubbles is hard. To make 1 micron
bubbles requires we pressurize air to three atmospheres. We could try to do
this by pushing high pressure air through one micron holes. But in practice
surface tension effects cause bubbles to stick to the hole and continue to
inflate to much larger sizes. Seitz presents an image of a tank filled with
micron scale bubbles generated by a commercial bubbler system (Figure 1).
However, I harbour a degree of scepticism for manufacturer claims of bubble
sizes especially below 10 μm, and from the images presented it appears the
lower 10 cm has cleared in 120 s, suggesting (from the Stokes equation) that
the bubbles are of the order 20 μm, consistent with my expectations for this
kind of technology. We could instead inject air into a high shear mixer and
break large bubbles down to smaller ones, like shaking up a bottle of soapy
water. Here we are relying on turbulence to transiently generate 3 atmospheres
of pressure throughout the mix. To do this by, say, shaking a drink bottle,
you’d need to generate ~150 g acceleration as you shake. Vortex mixers can do
this, but it is obviously an energy intensive process. Seitz calculates the
energy cost of 1 micron bubble production to be ~1 kW hr m-3 of air, a
theoretical limit which is unlikely to be obtained in practice. Seitz estimates
that to sustain a bubble concentration of 0.5 ppm bubbles (1 mg m-3) in the top
10 m of the ocean would require the injection of 50 million tonne of air a
year, if bubble stabilization for 20 hours could be achieved. Ignoring fixed
structures and coastline, 10 000 ships would have to disperse about 11 000 m3
of air a day. Each ship would need to generate 11 MW hr a day for bubble
generation, requiring 0.5 MW of dedicated generation. This is obviously a big
ask. We can reduce the scale of the task by being more targeted about where and
when we generate bubbles – by restricting deployment to the tropics where the
sun is nearly overhead, rather than the high latitudes where the sun is low in
the sky, and by timing bubble generation for daylight hours only.
Armwrestling thermodynamics
The biggest purely technical problem with the bright water idea is that
bubbles are thermodynamically unstable due to their high internal pressure,
with quite short lifetimes. An air bubble with 3 atmospheres internal pressure
will dissolve in water saturated with air at only 1 atmosphere. And the smaller
the bubble gets, the faster it dissolves. As observed above, a 10 μm bubble in
seawater lasted 10 seconds. A 1 μm bubble would presumably last a fraction of a
second. How can we fight this? Well, I can think of a few different ways. We
could try to make the bubble surface impermeable to air. Surfactants can
improve the barrier properties of surfaces to some kinds of molecular species.
Phospholipid bilayers, for instance, are impermeable to water. Unfortunately,
they do not present a significant barrier to nitrogen or oxygen molecules,
which are soluble in these surfactant layers. I don’t believe targeting the
barrier properties of bubbles will be successful. A second approach is to load
the bubble surface with a raft of fine particles or proteins, which can support
the two dimensional compressive load from surface tension, taking the pressure
off the air, rather like a microscopic diving bell. This behaviour is observed
in seawater bubbles. The long lived small bubbles reported by Johnson and Cooke
were observed to be stabilized by a shell of adsorbed matter (Figure 3). Could
this be a viable strategy for bubble stabilization? I don’t think so. Johnson
and Cooke report only “some” of the seawater bubbles they observed behaving
this way, so we know the yield of stabilized bubbles in natural seawater is
small. Stabilizing agents such as surfactants, and surface active proteins –
could be added to the water, but the material input would be enormous and
capture by low bubble concentrations hopelessly inefficient. And the observed
lifetimes are still only about 20 hours. A third strategy is to apply a bit of
thermodynamic jujitsu by adding a trace of an insoluble gas to the air, and use
the bubble shrinkage against itself. As the bubble shrinks, the insoluble gas
remains, and the partial pressure of the soluble gasses drops faster than the
internal pressure rises. The bubble eventually stabilizes at a smaller size.
Hydrogen is not very soluble in water. If 1% hydrogen were added to the air of
a 5 μm bubble, air leakage would be nearly arrested before it got to 1 μm. This
approach is actually used in medical ultrasound imaging, where stabilized
microbubbles are employed as acoustic contrast agents. The insoluble gases
favoured are perfluoroalkanes. These are more insoluble than hydrogen, and we
have performance data for this system. The lifetime of these bubbles in blood
is short – a half life of 1.3 minutes for one lipid stabilized perfluoroctane
bubble product. This does not bode well for bubble geoengineering. These
ultrasound contrast agents represent the best that we can do now, under ideal
conditions – a small volume, high value cost-no-object pharmaceutical product
that can bear the expense of exotic very insoluble gasses and sophisticated
lipid encapsulation stabilization strategies – and they still dissolve after a
few minutes (Figure 4). In the end, thermodynamics always wins.
Watercolours
Is there another way to look at this? The Achilles heel of the hydrosol
approach is the short bubble lifetime. But are there other ways to brighten
water? Are there any other micron sized light scattering particles cheaply
available in prodigious quantities, which float in water and don’t dissolve? It
turns out the answer is yes. Synthetic latex is produced on a huge scale –
1010kg in 2005. A latex is a dispersion of polymer microspheres in water
(Figure 5). The particle size is typically around 0.1 – 0.5 μm. The polymer
content is high – about 50% by weight. And its cheap – a bit over a dollar per
kilo wet. It looks like a bright white opaque liquid, like wood glue, which is
a polyvinylacetate latex. Its a bulk commodity used in adhesives, paper
coatings, paint and many other applications. The common polymers are
acrylates, polystyrene and its copolymers, PVA, and others. These polymers
themselves are inert and non toxic. Whether they present any physical risk to
the biota needs to be determined but given the small particle size and low
concentration in a milieu already loaded with natural micro- and nanoparticles
it seems low risk. The main safety concern in my opinion would be any residual
monomers, which are toxic. But these can be eliminated, certainly to the point
where these materials can be safely unleashed on the public as paints and
glues. The chief virtues of latex particles over bubbles is they don’t
dissolve, they don’t coalesce, they are durable, and they can be made much
smaller. They have a density of just over 1 g cm-3 so they sink, but at 0.2
micron the sedimentation velocity is too slow to matter. This presents a
different problem – the chief loss mechanism now is not dissolution but loss by
convection to deeper waters. Is there some way to keep these particles afloat?
I think there is. Most of these latex polymers, polystyrene, for example, are
hydrophobic – they’re water repellent. To keep the particles in suspension
requires added surfactants, or putting electrically charged groups on the
surface. But when diluted with salt water, both these stabilization mechanisms
fail. Without stabilization a polystyrene sphere will attach to the water
surface. Breaking waves will drive them under, but rising bubbles will scavenge
them back to the surface again. This mechanism is well known and extensively
studied in the mineral separation process of flotation, where particles of
mineral ores are recovered from slurries by attachment to rising bubbles. The
natural bubble population from breaking waves could keep even submicron
particles concentrated at and near the ocean surface (Figure 6). The use of
latex technology opens other doors for engineering particle properties. For
instance, rather than producing a particle composed of a single polymer, its
possible to construct a particle with two different polymers in a core-shell
morphology, or even hollow particles. Such particles can have much higher
scattering power than simple spheres, and are also made in bulk at commodity
prices. Indeed, they are used as opacifiers in paint. We could paint the oceans
white. Figure 6. Latex particles adsorbed on the surface of an oil droplet.
Similar behaviour would be observed at the air-water interface.
Painting by numbers
Lets run the numbers on this and ask, what would it take to reverse current
warming? First we need to know how much light these particles scatter back to
space. I used Mie theory to analyse scattering of 500 nm wavelength light
(roughly the solar peak) from 0.1 μm diameter polystyrene spheres, as if the
sun were overhead. The back scattering from these very small particles is
intense – 42% of overhead light returns to space. And this is just direct
scattering. Some of the light that scatters forward will scatter off a second
particle, and a third. Multiple scattering will see more than 42% of light
returned to space. Since these particles attach to the surface, lets consider,
for the moment, a monolayer on the water surface. This requires 1014 particles
per square metre, with a volume of 5.2×10-8 m3 per m2 (or 5 parts per billion
of the top 10 m, for comparison with Seitz’ figures). Polystyrene has a density
of 1050 kg m-3, so that’s a mass of 55 mg m-2. Over 3.16×1014 m2 of ocean
that’s 1.7×1010 kg polymer. What would this do to the earth’s energy balance?
Average insolation (accounting for cloud cover [Jin et al. 2002, cited by
Seitz]) is 239 Wm-2. The monolayer cross sectional area fraction is pi/4. So
the energy returned by direct overhead scattering is about 78 W. That’s huge
compared to the current CO2 forcing of about 2.25 Wm-2. Modelling reported by
Seitz indicates an increase of ocean albedo of 0.05 translates to an increase
of planetary albedo by 0.031 [Seitz 2010; Figure 5]. So I’ll assume planetary
albedo increase is 60% of the ocean albedo increase, which means we need ocean
backscattering of 3.75 Wm-2. We would only need 4.8% of a monolayer to offset
current CO2 forcing (ignoring the contribution from multiple scattering). 4.8%
of a whole ocean monolayer is 8.3×108 kg of dry polymer, or about 1.7×109 kg
wet latex. At say$1.20 per kg, this would cost $2.0 billion and account for 17%
of 2005 global production capacity. This is, surprisingly, well within reach.
$2.0b to reverse global warming is cheap. Restricting dispersal to the mid
latitudes where the greatest effect is achieved, using core-shell latex
technology, and properly accounting for multiple scattering would see this cost
drop even further. Annual growth in latex production grew organically by 4.5%
per annum between 2000-2005. Ramping production by 17% would be completely
feasible. The ongoing cost depends on the residence time of the particles at
the ocean surface. Equatorial currents run at about 1 ms-1, which would imply a
traversal time of about 1 year for the Pacific ocean. Mid latitude the currents
are much slower. The latex particles themselves will degrade in the
environment, and there will be losses by association and entrainment in a
complex marine environment. Figure 8. Major ocean surface currents. But let’s
provisionally estimate a cost of $2b per year. This is significantly cheaper
than, say, stratospheric sulfur aerosol injection which is estimated at $25-50b
per year, let alone space sunshades. And it doesn’t require exotic engineering,
enabling R&D, or orbital launches – it uses existing materials at a rate well
inside existing production capacity.
Conclusion
So consider this final elaboration of Russell Seitz’ bright idea: 0.1 μm
diameter latex particles, possibly hollow, or of core-shell morphology, bearing
a conventional stabilization system that is inactivated in salt water ensuring
that the particles are retained at and near the surface, are produced in bulk
using about 17% of existing production capacity and using commercial recipes,
and are sprayed onto the sea from tanks aboard ships or crop dusting aircraft,
oil rigs, and other structures, in the mid latitudes. For a cost in the order
of a mere $2b per year we could offset current global warming, subject to the
many disclaimers and qualifications discussed above, and many others not
mentioned. More limited, local applications, such as the direct cooling of
coral reefs as envisaged by Seitz for the microbubble concept, are also
possible. As they say on Top Gear, what could possibly go wrong --
You received this message because you are subscribed to the Google Groups
"geoengineering" group.
To unsubscribe from this group and stop receiving emails from it, send an email
[email protected].
To post to this group, send email to [email protected].
Visit this group at https://groups.google.com/group/geoengineering.
For more options, visit https://groups.google.com/d/optout.
--
You received this message because you are subscribed to the Google Groups
"geoengineering" group.
To unsubscribe from this group and stop receiving emails from it, send an email
[email protected].
To post to this group, send email to [email protected].
Visit this group at https://groups.google.com/group/geoengineering.
For more options, visit https://groups.google.com/d/optout.
--
You received this message because you are subscribed to the Google Groups
"geoengineering" group.
To unsubscribe from this group and stop receiving emails from it, send an email
to [email protected].
To post to this group, send email to [email protected].
Visit this group at https://groups.google.com/group/geoengineering.
For more options, visit https://groups.google.com/d/optout.
--
You received this message because you are subscribed to the Google Groups
"geoengineering" group.
To unsubscribe from this group and stop receiving emails from it, send an email
to [email protected].
To post to this group, send email to [email protected].
Visit this group at https://groups.google.com/group/geoengineering.
For more options, visit https://groups.google.com/d/optout.
