Stratospheric sulfate aerosols (geoengineering) june 2013

 

The ability of stratospheric sulfate aerosols to create a global dimming effect has made them a possible candidate for use in geoengineering projects to limit the effect and impact of climate change due to rising levels of greenhouse gases.^[2] Delivery of precursor sulfide gases such as sulfuric acid, hydrogen sulfide (H₂S) or sulfur dioxide (SO₂) by artillery, Aircraft and balloons has been proposed.Tom Wigley calculated the impact of injecting sulfate particles, or aerosols, every one to four years into the stratosphere in amounts equal to those lofted by the volcanic eruption of Mount Pinatubo in 1991,but did not address the many technical and political challenges involved in potential geoengineering efforts.If found to be economically, environmentally and technologically viable, such injections could provide a "grace period" of up to 20 years before major cutbacks in greenhouse gas emissions would be required, he concludes.
Direct delivery of precursors is proposed by Paul Crutzen.This would typically be achieved using sulfide gases such as dimethyl sulfide, sulfur dioxide (SO₂), carbonyl sulfide, or hydrogen sulfide (H₂S).These compounds would be delivered using artillery, aircraft (such as the high-flying F-15C)or balloons, and result in the formation of compounds with the sulfate anion SO₄^2-.

According to estimates by the Council on Foreign Relations, "one kilogram of well placed sulfur in the stratosphere would roughly offset the warming effect of several hundred thousand kilograms of carbon dioxide.


Geoengineering in general is a controversial technique, and carries problems and risks, such as weaponisation.However, certain problems are specific to, or more pronounced with this particular technique.

• Drought, particularly monsoon failure in Asia and Africa is a major risk.
• Ozone depletion is a potential side effect of sulfur aerosols;^[25][26] and these concerns have been supported by modelling.
• Tarnishing of the sky: Aerosols will noticeably affect the appearance of the sky, resulting in a potential "whitening" effect, and altered sunsets.
• Tropopause warming and the humidification of the stratosphere.
• Effect on clouds: Cloud formation may be affected, notably cirrus clouds and polar stratospheric clouds.
• Effect on ecosystems: The diffusion of sunlight may affect plant growth.but more importantly increase the rate of ocean acidification by the deposition of hydrogen ions from the acidic rain^[
• Effect on solar energy: Incident sunlight will be lower,which may affect solar power systems both directly and disproportionately, especially in the case that such systems rely on direct radiation.
• Deposition effects: Although predicted to be insignificant, there is nevertheless a risk of direct environmental damage from falling particles.
• Uneven effects: Aerosols are reflective, making them more effective during the day. Greenhouse gases block outbound radiation at all times of day.
• Stratospheric temperature change: Aerosols can also absorb some radiation from the Sun, the Earth and the surrounding atmosphere. This changes the surrounding air temperature and could potentially impact on the stratospheric circulation, which in turn may impact the surface circulation.

Further, the delivery methods may cause significant problems, notably climate change and possible ozone depletion in the case of aircraft, and litter in the case of untethered balloons.

Carbon dioxide (chemical formula CO₂) is a naturally occurring chemical compound composed of two oxygen atoms covalently bonded to a single carbon atom. It is a gas at standard temperature and pressure and exists in Earth's atmosphere in this state, as a trace gas at a concentration of 0.039 per cent by volume.
As part of the carbon cycle, plants, algae, and cyanobacteria use light energy to photosynthesize carbohydrate from carbon dioxide and water, with oxygen produced as a waste product.^[However, photosynthesis cannot occur in darkness and at night some carbon dioxide is produced by plants during respiration.Carbon dioxide is produced by combustion of coal or hydrocarbons, the fermentation of sugars in beer and winemaking and by respiration of all living organisms. It is exhaled in the breath of humans and land animals. It is emitted from volcanoes, hot springs, geysers and other places where the earth's crust is thin and is freed from carbonate rocks by dissolution. CO₂ is also found in lakes at depth under the sea, and commingled with oil and gas deposits.
The environmental effects of carbon dioxide are of significant interest. Carbon dioxide is an important greenhouse gas, warming the Earth's surface to a higher temperature by reducing outward radiation. Atmospheric carbon dioxide is the primary source of carbon in life on Earth and its concentration in Earth's pre-industrial atmosphere since late in the Precambrian eon has been regulated by photosynthetic organisms. Burning of carbon-based fuels since the industrial revolution has rapidly increased concentrations of atmospheric carbon dioxide, increasing the rate of global warming and causing anthropogenic climate change. It is also a major source of ocean acidification since it dissolves in water to form carbonic acid,which is a weak acid as its ionization in water is incomplete.

CO
2 + H
2O H
2CO
3

Carbon

spectrum.

See also: Molecular orbital diagram#Dioxide MO Diagram

In aqueous solution[edit]

Carbon dioxide is soluble in water, in which it reversibly converts to H
2CO
3 (carbonic acid).
The hydration equilibrium constant of carbonic acid is (at 25 °C). Hence, the majority of the carbon dioxide is not converted into carbonic acid, but remains as CO₂ molecules not affecting the pH.
The relative concentrations of CO
2, H
2CO
3, and the deprotonated forms HCO−
3 (bicarbonate) and CO2−
3(carbonate) depend on the pH. As shown in a Bjerrum plot, in neutral or slightly alkaline water (pH > 6.5), the bicarbonate form predominates (>50%) becoming the most prevalent (>95%) at the pH of seawater. In very alkaline water (pH > 10.4), the predominant (>50%) form is carbonate. The oceans, being mildly alkaline with typical pH = 8.2–8.5, contain about 120 mg of bicarbonate per liter.
Being diprotic, carbonic acid has two acid dissociation constants, the first one for the dissociation into the bicarbonate (also called hydrogen carbonate) ion (HCO₃⁻):

H₂CO₃ HCO₃⁻ + H⁺

K_a1 = 2.5×10⁻⁴ mol/litre; pK_a1 = 3.6 at 25 °C.

This is the true first acid dissociation constant, defined as , where the denominator includes only covalently bound H₂CO₃ and excludes hydrated CO₂(aq). The much smaller and often-quoted value near 4.16×10⁻⁷ is an apparent value calculated on the (incorrect) assumption that all dissolved CO₂ is present as carbonic acid, so that . Since most of the dissolved CO₂ remains as CO₂ molecules, K_a1(apparent) has a much larger denominator and a much smaller value than the true K_a1.
The bicarbonate ion is an amphoteric species that can act as an acid or as a base, depending on pH of the solution. At high pH, it dissociates significantly into the carbonate ion (CO₃²⁻):

HCO₃⁻ CO₃²⁻ + H⁺

K_a2 = 4.69×10⁻¹¹ mol/litre; pK_a2 = 10.329

In organisms carbonic acid production is catalysed by the enzyme, carbonic anhydrase.

Chemical reactions of CO₂

CO₂ is a weak electrophile. Its reaction with basic water illustrates this property, in which case hydroxide is the nucleophile. Other nucleophiles react as well. For example, carbanions as provided by Grignard reagents and organolithium compounds react with CO₂ to give carboxylates:

MR + CO₂ → RCO₂M (where M = Li or MgBr and R = alkyl or aryl).

In metal carbon dioxide complexes, CO₂ serves as a ligand, which can facilitate the conversion of CO₂ to other chemicals.
The reduction of CO₂ to CO is ordinarily a difficult and slow reaction:

CO₂ + 2 e⁻ + 2H⁺ → CO + H₂O

In physics, energy is an indirectly observed quantity which comes in many forms, such as kinetic energy, potential energy, radiant energy, and many others; which are listed in this summary article. This is a major topic in science and technology and this article gives an overview of its major aspects, and provides links to the many specific articles about energy in its different forms and contexts.
The question "what is energy?" is difficult to answer in a simple, intuitive way, although energy can be rigorously defined in theoretical physics.In the words of Richard Feynman, "It is important to realize that in physics today, we have no knowledge what energy is. We do not have a picture that energy comes in little blobs of a definite amount."
However, it is clear that energy is always an indispensable prerequisite for performing mechanical work, and the concept has great importance in natural science.The natural basic units in which energy is measured are those used for mechanical work; they always are equivalent to a unit of force multiplied by a unit of length. Other equivalent units for energy are mass units multiplied by velocity units squared.


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