Observing the Ozone Hole from Space: A Science Success Story

Using our unique ability to view Earth from space, we are working together with NOAA to monitor an emerging success story – the shrinking ozone hole over Antarctica.

Thirty years ago, the nations of the world agreed to the landmark ‘Montreal Protocol on Substances that Deplete the Ozone Layer.’ The Protocol limited the release of ozone-depleting chlorofluorocarbons (CFCs) into the atmosphere.

Since the 1960s our scientists have worked with NOAA researchers to study the ozone layer. 

We use a combination of satellite, aircraft and balloon measurements of the atmosphere.

The ozone layer acts like a sunscreen for Earth, blocking harmful ultraviolet, or UV, rays emitted by the Sun.

In 1985, scientists first reported a hole forming in the ozone layer over Antarctica. It formed over Antarctica because the Earth’s atmospheric circulation traps air over Antarctica.  This air contains chlorine released from the CFCs and thus it rapidly depletes the ozone.

Because colder temperatures speed up the process of CFCs breaking up and releasing chlorine more quickly, the ozone hole fluctuates with temperature. The hole shrinks during the warmer summer months and grows larger during the southern winter. In September 2006, the ozone hole reached a record large extent.

But things have been improving in the 30 years since the Montreal Protocol. Thanks to the agreement, the concentration of CFCs in the atmosphere has been decreasing, and the ozone hole maximum has been smaller since 2006’s record.

That being said, the ozone hole still exists and fluctuates depending on temperature because CFCs have very long lifetimes. So, they still exist in our atmosphere and continue to deplete the ozone layer.

To get a view of what the ozone hole would have looked like if the world had not come to the agreement to limit CFCs, our scientists developed computer models. These show that by 2065, much of Earth would have had almost no ozone layer at all.

Luckily, the Montreal Protocol exists, and we’ve managed to save our protective ozone layer. Looking into the future, our scientists project that by 2065, the ozone hole will have returned to the same size it was thirty years ago.

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Pinpointing the Cause of Earth’s Recent Record CO2 Spike

A new NASA study provides space-based evidence that Earth’s tropical regions were the cause of the largest annual increases in atmospheric carbon dioxide concentration seen in at least 2,000 years.

What was the cause of this?

Scientists suspect that the 2015-2016 El Niño – one of the largest on record – was responsible. El Niño is a cyclical warming pattern of ocean circulation in the Pacific Ocean that affects weather all over the world. Before OCO-2, we didn’t have enough data to understand exactly how El Nino played a part.

Analyzing the first 28 months of data from our Orbiting Carbon Observatory (OCO-2) satellite, researchers conclude that impacts of El Niño-related heat and drought occurring in the tropical regions of South America, Africa and Indonesia were responsible for the record spike in global carbon dioxide.

These three tropical regions released 2.5 gigatons more carbon into the atmosphere than they did in 2011. This extra carbon dioxide explains the difference in atmospheric carbon dioxide growth rates between 2011 and the peak years of 2015-16.

In 2015 and 2016, OCO-2 recorded atmospheric carbon dioxide increases that were 50% larger than the average increase seen in recent years preceding these observations.

In eastern and southern tropical South America, including the Amazon rainforest, severe drought spurred by El Niño made 2015 the driest year in the past 30 years. Temperatures were also higher than normal. These drier and hotter conditions stressed vegetation and reduced photosynthesis, meaning trees and plants absorbed less carbon from the atmosphere. The effect was to increase the net amount of carbon released into the atmosphere.

In contrast, rainfall in tropical Africa was at normal levels, but ecosystems endured hotter-than-normal temperatures. Dead trees and plants decomposed more, resulting in more carbon being released into the atmosphere.

Meanwhile, tropical Asia had the second-driest year in the past 30 years. Its increased carbon release, primarily from Indonesia, was mainly due to increased peat and forest fires -  also measured by satellites.

We knew El Niños were one factor in these variations, but until now we didn’t understand, at the scale of these regions, what the most important processes were. OCO-2’s geographic coverage and data density are allowing us to study each region separately.

Why does the amount of carbon dioxide in our atmosphere matter?

The concentration of carbon dioxide in Earth’s atmosphere is constantly changing. It changes from season to season as plants grow and die, with higher concentrations in the winter and lower amounts in the summer. Annually averaged atmospheric carbon dioxide concentrations have generally increased year over year since the 1800s – the start of the widespread Industrial Revolution. Before then, Earth’s atmosphere naturally contained about 595 gigatons of carbon in the form of carbon dioxide. Currently, that number is 850 gigatons.

Carbon dioxide is a greenhouse gas, which means that it can trap heat. Since greenhouse gas is the principal human-produced driver of climate change, better understanding how it moves through the Earth system at regional scales and how it changes over time are important aspects to monitor.

Get more information about these data HERE.

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Alkanes: Saturated Hydrocarbons

So you want to be an organic chemist? Well, learning about hydrocarbons such as alkanes is a good place to start…

Alkanes are a homologous series of hydrocarbons, meaning that each of the series differs by -CH2 and that the compounds contain carbon and hydrogen atoms only. Carbon atoms in alkanes have four bonds which is the maximum a carbon atom can have - this is why the molecule is described to be saturated. Saturated hydrocarbons have only single bonds between the carbon atoms.

The general formula of an alkane is CnH2n+2 where n is the number of carbons. For example, if n = 3, the hydrocarbon formula would be C3H8 or propane. Naming alkanes comes from the number of carbons in the chain structure.

Here are the first three alkanes. Each one differs by -CH2.


Shorter chain alkanes are gases at room temperature, medium ones are liquids and the longer chain alkanes are waxy solids.

Alkanes have these physical properties:

1. They are non-polar due to the tiny difference in electronegativity between the carbon and hydrogen atoms.

2. Only Van der Waals intermolecular forces exist between alkane molecules. The strength of these increase as relative molecular mass increases therefore so does the melting/boiling point.

3. Branched chain alkanes have lower melting and boiling points than straight chain isomers with the same number of carbons. Since atoms are further apart due to a smaller surface area in contact with each other, the strength of the VDWs is decreased.

4. Alkanes are insoluble in water but can dissolve in non-polar liquids like hexane and cyclopentane. Mixtures are separated by fractional distillation or a separating funnel.

The fractional distillation of crude oil, cracking and the combustion equations of the alkanes will be in the next post.

SUMMARY

  • Alkanes are a homologous series of hydrocarbons. Carbon atoms in alkanes have four bonds which is the maximum a carbon atom can have - this is why the molecule is described to be saturated. Saturated hydrocarbons have only single bonds between the carbon atoms.
  • The general formula of an alkane is CnH2n+2 where n is the number of carbons.
  • Shorter chain alkanes are gases at room temperature, medium ones are liquids and the longer chain alkanes are waxy solids.
  • They are non-polar.
  • Only Van der Waals intermolecular forces exist between alkane molecules. The strength of these increase as relative molecular mass increases therefore so does the melting/boiling point.
  • Branched chain alkanes have lower melting and boiling points than straight chain isomers with the same number of carbons.
  • Alkanes are insoluble in water but can dissolve in non-polar liquids like hexane. Mixtures are separated by fractional distillation or a separating funnel.

There’s a device that fits over your car’s exhaust pipe, captures pollution, and turns it into ink. Because exhaust contains the same material that ink is already made of, a company called Air Ink takes the carbon emissions collected from tailpipes, makes their own earth-friendly inks and markers, and simultaneously reduces pollution from both car exhaust and from the ink-making process. source

image via adweek

As Many Organic Reactions That I Could Cover In Two Hours

Alternatively titled, organic mechanisms cheat sheet. This was a real challenge and of course the detail isn’t there, but I have posts on combusting alkanes, fractional distillation/cracking of the alkanes, halogenoalkanes, organic nomenclature, basic alkanes and halogenoalkane nucleophilic substitution to give you some extra knowledge! And yes – I know some of these aren’t “mechanisms” in the sense of the curly arrow kind.

Halogenoalkanes

[1] Mechanism: free-radical substitution

This reaction involves atoms being replaced by other atoms (in this case, free-radicals). Free radicals have a single unpaired electron, formed if a bond splits evenly and each atom gets one of the two electrons (called homolytic fission).

Examples: chlorination of methane, bromination of methane etc.

Process

Beginning with initiation (1), chlorine-chlorine covalent bonds break symmetrically by absorbing UV light, forming free radicals that have an unpaired electron in the outer shell that makes them particularly reactive.

The second step is propagation (2), where the free radicals react with methane molecules to form hydrogen chloride gas and leaving a methyl free radical which then goes on to react with a second chlorine molecule to form chloromethane and another free radical (3). This continues in a chain reaction.

Termination must occur to stop the chain reaction. This can happen several ways. In the top reaction of (4), chlorine can reform but would not terminate the reaction since UV light just breaks it down again. Another option is the two free radicals forming a chloromethane or forming ethane (C2H6, shown structurally in the diagram).

Product: halogenoalkane

Overall Equation: CH4 + Cl2 -> CH3Cl + HCl

Conditions: UV light, halogen (usually from a CFC), alkane

[2] Mechanism: nucleophilic substitution by a hydroxide ion

In this reaction, the polar C-H bond is susceptible to nucleophilic attack by the nucleophilic ion hydroxide. A nucleophile is an electron pair donor. The reaction can also be called a hydrolysis reaction since it breaks chemical bonds with hydroxide ions.

Example: bromoethane and sodium hydroxide

Process

This is how the mechanism for this would be drawn. Here’s what’s happening – the lone pair on the hydroxide ion is attracted to the slightly positive carbon. Since it cannot make five bonds, when the nucleophile makes the bond, the bond between the C-Br “breaks” and bromine takes the electron to become a halide ion. Remember, curly arrows show the electron movement. The halide then combines with the sodium ions to form sodium bromide.

Product: alcohol

Overall equation: CH3CH2Br + NaOH -> CH3CH2OH + NaBr

Conditions: aqueous sodium or potassium hydroxide, refluxed (continually boiled and condensed), halogenoalkane dissolved in ethanol

[3] Mechanism: nucleophilic substitution by a cyanide ion

In this reaction, the polar C-H bond is susceptible to nucleophilic attack by the nucleophilic ion cyanide (C triple bonded to H). A nucleophile is an electron pair donor.

Example: bromoethane and potassium cyanide

Process

 This is how the mechanism for this would be drawn. Here’s what’s happening – the lone pair on the cyanide ion is attracted to the slightly positive carbon. Since it cannot make five bonds, when the nucleophile makes the bond, the bond between the C-Br “breaks” and bromine takes the electron to become a halide ion. Remember, curly arrows show the electron movement and in this reaction, there is an extra carbon added. This can be confusing and I’ve added just a triple bond to the second carbon before, but that is wrong. The halide then combines with the potassium ions to form potassium bromide.

Product: nitrile

Overall equation: CH3CH2Br + KCN -> CH3CH2CN + KBr

Conditions: aqueous potassium cyanide, refluxed (continually boiled and condensed), bromoethane dissolved in ethanol

[4] Mechanism: nucleophilic substitution by an ammonia molecule

In this reaction, the polar C-H bond is susceptible to nucleophilic attack by the nucleophilic ion ammonia (ammonia can donate a pair of electrons). However, it is a neutral molecule. This mechanism has a few stages.

Example: bromoethane and ammonia

Process

This is how the mechanism for this would be drawn. Here’s what’s happening – the lone pair on the ammonia is attracted to the slightly positive carbon. Since it cannot make five bonds, when the nucleophile makes the bond, the bond between the C-Br “breaks” and bromine takes the electron to become a halide ion. Remember, curly arrows show the electron movement. This is shown by the first step.

The nitrogen becomes positive, with four bonds. Another ammonia molecule is attracted to the hydrogen and removes it from the intermediate stage (remember, this happens instantly and is only in this stage for a very short amount of time) to become an ammonium ion. The product left over is a amine, and the ammonium ion reacts with the bromine to form NH4Br.

Product: amine (primary, secondary or tertiary; primary is obtained if a concentrated solution of ammonia is used since further substitution can occur from the lone pair on the amine molecule).

Overall equation: CH3CH2Br + 2NH3 -> CH3CH2NH2 + NH4Br

Conditions: concentrated ammonia in excess, sealed container under pressure, bromoethane dissolved in ethanol

[4] Mechanism: elimination reaction by a hydroxide ion

Hydroxide ions can act as nucleophiles or electrophiles depending on what solution they are in. In ethanol, hydroxide ions act as a base so accept protons to form water. Elimination reactions are where small molecules are removed from organic compounds.

Example: bromopropane and ethanolic solution of potassium hydroxide

Process

 This is how the mechanism for this would be drawn. Here’s what’s happening – the hydroxide accepts a proton (a hydrogen atom) so a carbon-carbon double bond forms between the carbon that just had a hydrogen taken away and the one next to it. This happens to a carbon adjacent to the C-Br bond, since the Br is then removed as a halide ion upon the formation of the double bond. The hydrogen that has been taken away forms water and the product left over is an alkene

Product: alkene

Overall equation: CH3CHBrCH3 + KOH (in ethanol) -> CH2CHCH3 + + H2O + KBr

Conditions: ethanolic solution of potassium hydroxide, bromoethane dissolved in ethanol

Alkenes

[1] Reaction: addition polymerisation

Alkenes react with other alkenes to form polymers, which make up plastics. Polymers made from an addition process are called addition polymers and they’re pretty simple, named after the alkene they form, e.g. ethane forms poly(ethene).

Example: polyethene

Process

Polymers are repeating chains of carbon atoms. The unit that repeats is the monomer, e.g. ethene.

Product: polymer

Overall equation: n[CH2CH2] -> [CH2CH2]n

Good to know: addition polymers are unreactive since they have no C=C bond, so are good inert materials such as insulators or packaging.

[2] Mechanism: electrophilic addition reactions of hydrogen bromide

Hydrogen bromide is a polar electrophile (proton acceptor). The double bond has an area of high electron density so electrons move from the double bond to the hydrogen of the hydrogen bromide.  

Example: ethene and hydrogen bromide

Process 

This is how the mechanism for this would be drawn. Here’s what’s happening – the electrons move from a delta negative region to a delta positive region (the hydrogen). Electrons then move from the H to the Br, which becomes a halide ion. Now that one carbon is bonded to a hydrogen, the remaining carbon is a carbocation (a positively charged carbon). The halide ion, with a negative charge, is then attracted to the positive charge. The double bond has been broken and the HBr has been added across the double bond.

Product: halogenoalkane

Overall equation: CH2CH2 + HBr -> CH3CH2Br

Conditions: can happen even at temperatures below room temp

[3] Mechanism: electrophilic addition reactions of concentrated sulfuric acid

Concentrated sulfuric acid is a polar electrophile (proton acceptor). The double bond has an area of high electron density which means an electrophilic addition can take place.

Example: ethene and sulfuric acid

Process

This is how the mechanism for this would be drawn. Here’s what’s happening – the electrons move from a delta negative region (double bond) to a delta positive region (the hydrogen). Electrons then move from the H to the O, which becomes a hydrogen sulfate ion. Now that one carbon is bonded to a hydrogen, the remaining carbon is a carbocation (a positively charged carbon). The sulfate ion, with a negative charge, is then attracted to the positive charge on the carbocation. The double bond has been broken and the H2SO4 has been added across the double bond.

Product: akyl hydrogensulfate

Overall equation: CH2CH2 + H2SO4 -> CH3CH2(H2SO4)

Conditions: can happen even at temperatures below room temp

[4] Mechanism: electrophilic addition of bromine

There is no difference in charge across Br2, but it is still an electrophile. The reaction will be coloured since bromine is a distinct brown/orange.

Example: ethene and bromine

Process

This is how the mechanism for this would be drawn. Here’s what’s happening – when the bromine moves closer to the double bond, it gets a slight induced dipole. One bromine then takes the electrons and the electrons from the Br-Br bond go to the end bromine. This then has a lone pair to be attracted to the carbocation.

Product: halogenoalkane

Overall equation: CH2CH2 + Br2 -> CH2BrCH2Br CH2

Conditions: bromine bubbled through alkene, absence of light, temperature below room temp.

Alcohols

[1] Reaction: oxidation

Oxidation is simply the use of an oxidising agent. A primary alcohol is oxidised to produce an aldehyde, then further oxidised to a carboxylic acid. A secondary alcohol is only oxidised to a ketone. A tertiary alcohol is not oxidised.

Process

Primary alcohols lose two hydrogen atoms, one from the O-H group and one from the fully saturated carbon. In the second oxidation, an oxygen is added the remaining carbon.

Secondary alcohols lose a hydrogen to form a ketone which cannot be oxidised further. Tertiary alcohols cannot be easily oxidised since they do not have two hydrogen atoms bonded to the carbon bonded to the –OH group.

Product: aldehyde, carboxylic acid, ketone

Conditions: Primary – oxidising agent in excess to produce a carboxylic acid and refluxed mixture, or distilled off product and alcohol in excess to get the aldehyde. Secondary – refluxed gently with an excess of oxidising agent.

Good to know: Acidified potassium or sodium dichromate (V) is good at oxidising alcohols. The dichromate ion CrO7 2-, is orange and gets reduced to the green chromium(III) ion, Cr3+ when the alcohol is oxidised.

[2] Mechanism: elimination reaction with concentrated sulfuric acid

This reaction can be called a dehydration reaction since a molecule of water is eliminated.

Process

The mechanism above is very simplified since the one for sulfuric acid is fairly complicated. Here’s what’s going on – the oxygen in the –OH group has a lone pair which donates electrons to a H+ ion (usually on the end of a H2SO4 molecule). This means A (which would be the oxygen on a hydrogen sulfate ion) takes the electrons in the bond. The water is then lost from the molecule, forming a carbocation. This then means the hydrogen sulfate (A) ion can remove the H+ ion from the carbocation and the double bond can form between the two carbons.

Product: alkene

Overall equation: CH3CH2OH + H2SO4 -> CH2CH2 + H2O + H2SO4

Conditions: concentrated sulfuric acid catalyst 170 degree temperature, or by passing alcohol vapour over a heated (Al2O3) aluminium oxide catalyst at 600 degrees.

HAPPY STUDYING!