Again, Guess What’s Being Described

We’re not looking for the name of the clouds in the picture. If we were, we might mistake them for cirrus clouds, whose quantity is probably affected by our mystery.

Helkivad_ööpilved_Kuresoo_kohalS
Noctilucent clouds above Estonia. From Wikipedia

In fact, the bluish clouds are noctilucent clouds composed of ice particles that crystallise around meteoric dust. In the late 1800s, the astronomer Otto Jesse examined simultaneous pictures that were taken 35 km apart, and by comparing the clouds to the position of a star, he obtained a parallax angle. Using a tangent ratio, he calculated that they were 82 000 metres above us, at about 13 times the altitude of cirrus. For a while it was believed that an increasing number of  noctilucent clouds had been forming, serving as a canary for a problem caused by our mystery. But with more data it turns out that the frequency of the formation of this cloud-type oscillates.

We are looking for something that combines with water to convert mica and feldspar into salt, sand and clay. An 18th century Scottish doctor described it as a diamond dissolved in vital air. Both its physical and chemical properties make it essential to life. Until the middle of the 20th century, it was also believed to be the source of that vital air, but that belief turned out to be mistaken.

It is part of a great cycle. Rain, oceans and the most common protein on earth remove it from the air. Volcanoes, mitochondria, and certain human activities return it to the atmosphere. Our mystery absorbs part of the electromagnetic spectrum by stretching asymmetrically and bending in two different ways, so if found in excess, it disturbs the planet far more profoundly and objectively than the way the rock band INXS perturbs my peace of mind.

I was offended by a Fraser Institute brochure that was once once distributed to Canadian schools. It claimed that because the percentage of the mystery is so small relative to the rest of its constituents, it could not possibly be harmful—an odd argument to make, given, for example, the lethal does of botulism toxin. Others such as Bjorn Lomborg do not dispute that its increasing quantity is significant but pretend that the consequences are exaggerated. I wish he knew what he was talking about. Scholar Howard Friel’s  The Lomborg Deception systematically tears apart Lomborg’s thesis; it had gained credibility only because most readers had not dug into the book’s sources. Others feel so threatened by the social and political solutions being proposed to reduce the amount of the mystery that they fund all sorts of organizations to misrepresent the truth. Here is a list of those receiving such funds:

Figure 2
From desmogblog.com

The German word for our mystery has 17 letters, and it is derived from their word for coal, kohlen.  When burnt, coal produces more of the answer to our puzzle than any other fossil fuel.

global_emissions_gas_2015
Greenhouse gases based on Co2equivalents. The impact from fossil fuels is even greater than the pie chart suggests because almost 1/3 of the human-produced methane is released from extracting fossil fuels. The latter also contribute some of the N2O. Compared to CO2, certain fluorine-containing gases are, on average, about 10 000 times more efficient at absorbing infrared. Luckily, those gases along with methane and nitrous oxide are not as abundant as CO2. Source: IPCC(2014) but based on 2010 global emissions.

 

 

Other sources:

Cirrus Clouds and Climate Change http://www.nature.com/nclimate/journal/v1/n1/full/nclimate1068.html

Lectures on the Elements of Chemistry: Delivered in the University of Edingburg …, Volume 1
By Joseph Black

JosephBlackLectures

Noctilucent clouds—not a canary for climate change http://onlinelibrary.wiley.com/doi/10.1029/2003EO280001/epdf

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Two Offbeat Questions About Greenhouse Gases

In science, something fruitful can arise from innocent or atypical questions.  One of many examples of this was a recent query in Quora, ” Can chlorine be potentially a greenhouse gas? Why or why not?

Here’s what I wrote, but I’ve since added a little more detail.

Short answer , no.  🙂

Now here’s why….

An infrared spectrum is used to check if specific molecules are good absorbers of infrared energy, which qualifies them as “greenhouse gases”. Some chlorine-containing gases like CFCs fall into that category, but diatomic chlorine(Cl2) or monoatomic chlorine(Cl) do not. How come?

In order for molecular vibrations to absorb IR energy, the vibrational motions along the bond must change the dipole moment CO2IRof the molecule. A dipole occurs when pulling forces within a molecule do not cancel out. Why are there forces in the first place? These exist because of the differences in “greediness” for electrons between different atoms. So Cl by itself has no bonds so it can’t even vibrate. Diatomic chlorine does not meet the criteria either because, like O2 and N2 in air, it has the same atom pulling on each side of the bond, and equally important, any type of stretching or bending will not cause or lead to a change in net force between the bonded atoms.
The neat and thing about CO2 is that it doesn’t have a permanent dipole moment, but it can experience a net force during an asymmetric stretch. This happens when one oxygen gets squished towards the carbon in the middle of the molecule while the other oxygen atom stretches away, leading to a change in dipole. That’s what makes carbon dioxide a greenhouse gas. If the oxygen atoms each pull away from the carbon, the net force will still equal zero. With no net change, the symmetric stretch cannot intensify and cannot absorb infrared energy.

co2 asymm
CO2’s asymmetric stretch, which leads to strong absorption of infrared Source for 3 gifs.
co2 symm
This symmetric stretch cannot intensify with incoming infrared red absorption.

There is also some absorption in another part of the infrared spectrum, although not as intense but still due to a change in dipole. It happens when the CO2 molecule bends.

co2 bend
A bending vibration of the CO2 molecule. The change in dipole occurs, implying that it can intensify by absorbing infrared.

At the rish2o symmk of belaboring the idea, let’s point look at the H2O molecule, a strong and more abundant greenhouse gas than CO2.  The latter has a linear shape. Due to  water’s angular shape, water already has an overall dipole.  Even with a symmetric stretch a change in dipole will result. Specifically, the movement shown increases the net pull of oxygen. As a result such a stretch can also be amplified when it absorbs infrared.

By the way, why don’t we focus any attention on our emissions of water vapor? Simplistically, one might attribute it to relative numbers. Air on average is about 2% H2O gas. (The percentage breakdowns for atmospheric composition that are normally given are for dry air.) So although the combustion of petroleum and natural gas emits H2O, relative to CO2, the water produced causes very little change in the overall percentage of water vapor. Moreover, coal, which produces the most CO2 per kWh, produces little water when burnt because hydrogen only makes up about 5% of coal.  There is a net movement of water from land to ocean of 37 trillion tons of water per year. Of this total, about 12 trillion tons of water is in the air at any one time because water vapor only stays in the air for an average of 10 days. That’s 12 000 gigatons, of which we add about 3 to 5 gigatons(Gton) annually, a change of 0.03%. In contrast, we add 9 Gtons of carbon dioxide annually. After an increased withdrawal by oceans and land, there is a net annual  input of 4 Gtons to a pool of 840 Gtons, or a 0.5% increase, more than 15 times bigger than that of water.

But far more importantly,  in the real world’s dynamics, CO2 and other non-H2O greenhouse gases, are the major limiting factor in the greenhouse effect.

Without non-condensing greenhouse gases[such as CO2], water vapor and clouds would be unable to provide the feedback mechanisms that amplify the greenhouse effect.

488311main_feedback-forcings

Other references for the above research:

Andrew Lacis. NASA Goddard Institute Space Studies. CO2: The Thermostat that Controls Earth’s Temperature 2010

Lacis, Hansen and al. NASA GISS  The role of long-lived greenhouse gases as principal LW control knob that governs the global surface temperature for past and future climate change 2013

….

I encountered the second question on a NASA blog. It’s based on a common misconception, but again it shows how even someone without the erroneous idea can still benefit from reading a thorough answer, such as the one given below by Rebecca Lindsey. The ozone hole and global warming are separate problems, but some of the minor connections between the two are rarely discussed in big media.

Are the ozone hole and global warming related ?

 By Rebecca LindseySeptember 14, 2010

The ozone hole and global warming are not the same thing, and neither is the main cause of the other.

The ozone hole is an area in the stratosphere above Antarctica where chlorine and bromine gases from human-produced chlorofluorocarbons (CFCs) and halons have destroyed ozone molecules.

Global warming is the rise in average global surface temperature caused primarily by the build-up of human-produced greenhouses gases, mostly carbon dioxide and methane, which trap heat in the lower levels of the atmosphere.

There are some connections between the two phenomena.

For example, the CFCs that destroy ozone are also potent greenhouse gases, though they are present in such small concentrations in the atmosphere (several hundred parts per trillion, compared to several hundred parts per million for carbon dioxide) that they are considered a minor player in greenhouse warming. CFCs account for about 13% of the total energy absorbed by human-produced greenhouse gases.

The ozone hole itself has a minor cooling effect (about 2 percent of the warming effect of greenhouses gases) because ozone in the stratosphere absorbs heat radiated to space by gases in a lower layer of Earth’s atmosphere (the upper troposphere). The loss of ozone means slightly more heat can escape into space from that region.

Global warming is also predicted to have a modest impact on the Antarctic ozone hole. The chlorine gases in the lower stratosphere interact with tiny cloud particles that form at extremely cold temperatures — below -80 degrees Celsius (-112 degrees Fahrenheit). While greenhouse gases absorb heat at a relatively low altitudes and warm the surface, they actually cool the stratosphere. Near the South Pole, this cooling of the stratosphere results in an increase in polar stratospheric clouds, increasing the efficiency of chlorine release into reactive forms that can rapidly deplete ozone.

  1. References:

  2. Allen, Jeannie. (2004, February 10). Tango in the Atmosphere: Ozone and Climate Change. Earth Observatory. Accessed: September 14, 2010.

  3. Baldwin, M.P., Dameris, M., Shepherd, T.G. (2007, June 15). How will the stratosphere affect climate change?Science, 316 (5831), 1576-1577.

  4. Intergovernmental Panel on Climate Change, (2007). Summary for Policymakers. In Climate Change 2007: The Physical Science Basis. Contribution of Working Group I to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change. [Solomon, S., D. Qin, M. Manning, Z. Chen, M. Marquis, K.B. Averyt, M. Tignor, and H.L. Miller (eds.)]. Cambridge, United Kingdom, and New York, New York: Cambridge University Press.

  5. Ozone Hole Watch. Accessed: September 14, 2010.

Even When Pure, Water Is Blue

We have all seen supposedly colorless water in a glass and in raindrops on a windshield. If there’s little air in it, water even looks colorless when it forms ice cubes. The fixed but incorrect idea that water is intrinsically without color survives in many of our minds even though we all observe various shades of blue in snow or glaciers or in large bodies of water.

If you put a bit of shampoo in your hand, you will notice that it looks a little lighter in color than when it sits in a bottle. This makes us aware that light’s path length (as light moves across a transparent object) influences the intensity of color. Could it be that water only appears colorless when there are not enough molecules in light’s path to remove some of white light’s components?

I like to demonstrate this by simply using a large 8 inch white mixing bowl. If it’s only 1/4 filled, the water still appears like it does when coming out of the tap. But when about 3/4 full, a pale blue colour becomes obvious. The bowl’s white background helps because light bounces back and forth within it, allowing even more vibrating water molecules to absorb a red portion of the spectrum. Deprived of a bit of red, water in most of its forms consequently transmit a pale blue light.

color_water

colr_water3One can argue that the tap water I used is not pure. Admittedly, various ions, algae and even suspended silt and mud can definitely introduce all sorts of green and brown hues. If you fill a mixing bowl with deionized water from the lab, which is created by forcing water through an impurity-removing column, the water is still colored.
Here’s another picture that looks less greyish. It was obtained by placing the same deionized water in a narrower but taller white container.

According to the Journal of Chem Ed authors, a better way to demonstrate this is to use a 3 m long by 4 cm diameter length of aluminum tubing with a Plexiglass window epoxied to one end of the tube. I tried it with a 2.5 m by 4 cm plastic pipe, sealed with a glass stopper. When I photographed it with a flash, I did see a beautiful blue color, but my control (a picture of the pipe without the water) appeared just as blue!

In order to eliminate the scattering of blue light from suspended particles in water, it’s not enough to use deionized water. Microfiltration is also necessary. Once that variable is removed, the persistent blue is sure to come from the 3rd overtone of the oxygen-hydrogen stretching vibration of the water molecule.

In fact, the only way that water will leave white light alone is if its hydrogen atoms are replaced with a heavier form called deuterium. The key absorption peak then shifts into the invisible infrared. The following spectra are from the J of Chem Ed reference cited below, and I’ve pointed out the differences between purified and deuterated water.

water_0

 color wavelength range(nm)
 violet  380–450
 blue  450–475
 cyanide  475–495
 green  495–570
 yellow  570–590
 orange  590–620
 red  620–750

colorwheel_0If you have the artist’s color wheel in mind, you may be confused by the absorption of red leading to the transmission of blue. Although red’s opposite is green, red’s wide range of wavelengths is actually complementary to all hues of green, cyanide and blue. I’ve drawn a color wheel which is proportional to perceived wavelengths to illustrate this point.

Don’t feel bad if you were unaware of the color of water. You have company. When Kurt Nassau published his book on colour in 1983, and even a decade later when an excellent article in the Journal of Chemical Education appeared on the subject, the authors pointed out that many scientists were under the illusion that water was intrinsically without color. I looked through my own books and found in The Flying Circus of Physics a completely incorrect explanation for why a lake can seem blue, attributing it mainly to reflections from the surface.

REFERENCES

Charles L. Braun and Sergei N. Smirnov. Why is Water Blue? J. Chem. Edu., 1993, 70(8), 612

Kurt Nassau. The Physics and Chemistry of Color: the 15 Causes of Color. Wiley-Interscience. 1983

http://en.wikipedia.org/wiki/Color_of_water

Jearl Walker. The Flying Circus of Physics. Wiley and Sons. 1977

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