Major
Gases:
Nitrogen
----------------------------------
Oxygen
Why does oxygen have the percentage it does in our atmosphere? Imagine that it was much higher than it is. The rate of combustion due to forest fires would increase, lowering the percent of oxygen. Suppose that it was much lower than it is today. The rate of combustion due to forest fires would decrease, and if O2 were low enough, even respiration would decrease. This would cause the amount of oxygen to rise again. So the amount of oxygen is self-regulating, and it is unlikely that, since the accumulation of oxygen in the atmosphere after the formation of BIFs and the development of forests and large, multicellular animals, the percentage of oxygen has been much more than a few percent higher or lower than it is today, about 21%.
Argon
Noble gas; chemically unreactive.
----------------------------------
Carbon Dioxide
Carbon dioxide is one of a group of gases known as "Greenhouse Gases", and as a result of Fossil Fuel Burning over the past 150 years, it's increased by 30%*. Greenhouse gases
(data from Dave Keeling and Tim Whorf, Scripps Inst. of
Oceanography)
In the diagram above, the lower graph is a proxy for glacial ice volume. When the curve goes down, glaciers were advancing. When the curve goes up, glaciers were melting. Notice that the atmospheric CO2 content decreases during ice ages. Click on the image for more information.
A consensus has emerged among scientists and scientific organizations worldwide that as a result of the interaction of greenhouse gases with other factors controlling the earth's temperature, global temperatures have risen, and we can expect them to continue to rise into the foreseeable future. This will be discussed under the section on "Radiation Balance".
Minor (Trace) Gases:
Neon
Noble gas; chemically unreactive.
----------------------------------
Helium
Noble gas; chemically unreactive.
----------------------------------
Methane
On left: overall change from 0 to 2000CE. On right: change just from 1984 to 2017.
(Note that the vertical axis STARTS on the right at 600 ppb and ends at 1800 ppb, so the increase from 0 to 2000CE is around 3x rather 10x as it looks. Still a very significant increase. From https://www.pnas.org/content/116/8/2805)
The increase in Methane seen here beginning with the Industrial Revolution is due to the planetary rise in human population as improvements in medical sciences and agriculture have enabled both longer life spans and more people.
Methane is one of a group of gases known as Greenhouse Gases. These are gases that absorb infrared light. The gas molecules that absorb that energy warm up, and re-radiate that heat in all directions, including back down to the Earth. Although there is relatively little methane in the atmosphere compared to other greenhouse gases like CO2 and H2O, it is a very effective absorber of infrared light. Gram for gram, it is 25 times more effective than CO2.
This will be discussed under the section on "Radiation Balance".
Krypton
Noble gas; chemically unreactive.
----------------------------------
Hydrogen
----------------------------------
Water
Water is the single most variable component of the atmosphere, varying from nearly 0 to as much as 4% by weight. The percentages of atmospheric gases quoted in the table in the previous web page are for "dry" air; i.e. without water.
I have an entire web page discussing water vapor in the atmosphere, if you are interested in going into this in more detail. It will be covered in ESC1000, but not in OCE1001, so if you are taking Oceanography you do not have to read it.
Pollutant Gases:
Carbon Monoxide
Unlike CO2, CO is extremely toxic. It combines with hemoglobin in blood much more strongly than O2, so if you breath even small amounts of CO in, hemoglobin cannot transfer the oxygen your cells (especially brain cells) need, they are starved of oxygen, and you die. This is why it is so important to not run a car in an enclosed area like a garage with the doors closed, and why running a kerosene heater indoors is so dangerous. Over 400 people die EVERY year in the US from carbon monoxide poisoning, and thousands more wind up in emergency rooms. Please be very careful when you are dealing with autos and combustible materials indoors.
One of the primary purposes of "catalytic converters" in automobile exhaust systems is to convert the CO into CO2.
----------------------------------
Ammonia
Ammonia [NH3] and nitrous oxides react with water in the atmosphere to produce nitric acid, which is one of the two main components of acid rain. As a result, there are strong incentives for countries to reduce their nitrogen-bearing emissions.
----------------------------------
Nitrous Oxides
Besides being a contributor to acid rain, some nitrous oxides (combinations of nitrogen and oxygen) are also potent greenhouse gases. In particular, N2O is, gram for gram, around 300x more effective than CO2. However, there is less than 1/1000 as much N2O as there is CO2, so the effect is smaller.
----------------------------------
Sulfur Dioxide
Sulfur dioxide is important in the atmosphere for 2 reasons. First, like the nitrogen compounds above, SO2 reacts with water in the atmosphere to produce sulfuric acid, which is the other main component of acid rain. Second, SO2 is an anti-greenhouse gas, and reflects sunlight. Because volcanic eruptions commonly emit SO2, large volcanic eruptions at times have caused significant global cooling.
The asteroid impact 65 million years ago in the Yucatan Peninsula vaporized sulfur-rich carbonate sediments, causing a series of changes - global cooling caused by the SO2 , followed by acid rain, and eventually probably global warming due to huge amounts of CO2 from the carbonate sediments. That combination of events not only caused the extinction of the dinosaurs, but many other terrestrial and marine organisms.
Injection of SO2 into the stratosphere has been suggested because of the anti-greenhouse effect of SO2.
----------------------------------
ChloroFluoroCarbons
ChloroFluoroCarbons (AKA "Freon") are a family of commercially valuable manufactured chemicals. They were used as refrigerants and as aerosol propellants because they are non-toxic, stable, and have good thermodynamic properties. Unfortunately, as is described in the Atmosphere web page, they also catalytically destroy Ozone molecules in the stratosphere, and as a result they have caused significant damage to the Ozone Layer which protects us from UV light from the Sun.
Because of the fact that CFCs destroy ozone, an international agreement, the "Montreal Protocol" was enacted in 1987 and begun in 1989, which banned the production of CFCs worldwide. The damage to the Ozone Layer is now being seen to be healed, and we can look forward to at time in the future where the Ozone Layer will be back to its pre-1980 level in another 30-50 years.
Nitrogen
----------------------------------
Oxygen
Why does oxygen have the percentage it does in our atmosphere? Imagine that it was much higher than it is. The rate of combustion due to forest fires would increase, lowering the percent of oxygen. Suppose that it was much lower than it is today. The rate of combustion due to forest fires would decrease, and if O2 were low enough, even respiration would decrease. This would cause the amount of oxygen to rise again. So the amount of oxygen is self-regulating, and it is unlikely that, since the accumulation of oxygen in the atmosphere after the formation of BIFs and the development of forests and large, multicellular animals, the percentage of oxygen has been much more than a few percent higher or lower than it is today, about 21%.
Argon
Noble gas; chemically unreactive.
----------------------------------
Carbon Dioxide
Carbon dioxide is one of a group of gases known as "Greenhouse Gases", and as a result of Fossil Fuel Burning over the past 150 years, it's increased by 30%*. Greenhouse gases
* - it was 30% when I 1st made this webpage
in the late 1990s. As
of 2015, it has increased to 43% above pre-industrial
levels, a new record. It continues to rise.
 As of ~2008 |
 As of 2017 |
These curves are based on
data from an atmospheric observatory on Mauna Loa,
Hawaii. Why measure the atmosphere there?
- Aside from the fact that it's a very nice place, Hawaii is in the central Pacific, far from any continent or major population centers.
- High up on the volcano, it should be
also isolated from pollution from any nearby cities.
- As isolated as it is, by the time the atmosphere reaches the observatory, it should be relatively well mixed,
- and therefore measuring the
composition of the atmosphere there should give a good
"average" composition of the world atmosphere.
- A cyclic, seasonal change.
- When the overall rise is subtracted from the data, you see a consistent seasonal change: a rise from October through May, then a decrease from May through September.
- Why? Because photosynthesis
during the summer draws down CO2 in the
atmosphere.
- And during winter, days are shorter, temperatures are low, many trees drop their leaves, and respiration from organisms adds CO2 to the atmosphere.
- Those of us who are aware that summer in the Northern Hemisphere also means that it's winter in the Southern Hemisphere may wonder why the two don't cancel each other out.
- The answer is that most of the world's land area (where rates of photosynthesis are much higher than in the ocean) is in the Northern Hemisphere. And of the land masses in the Southern Hemisphere, Antarctica is mostly covered by ice and much of Australia is arid.
- Which means that photosynthesis is dominated by the Northern Hemisphere,
- and during Northern Hemisphere spring and summer, world CO2 decreases, and during fall and winter, it rises.
- An overall rise in CO2 from 1958 to the present (and incidentally, the observatory is still in operation and continues to show a rise).
- Data from air bubbles trapped in glaciers show that the rise began around the time that the Industrial Revolution began
- Data from carbon isotopes show that this is "old" carbon, from the burning of fossil fuels.
- We also have data going back hundreds of thousands of years from glacial ice bubbles (see below).
- Over the last 650,000 years, CO2 has varied in time with the Ice Ages.
- Note that at no time over the last
650,000 years (and this record has been extended to
about 750,000 years now) has CO2 been over 300
parts per million (ppm), and now it is over 400
ppm. This is a significant global change.
In the diagram above, the lower graph is a proxy for glacial ice volume. When the curve goes down, glaciers were advancing. When the curve goes up, glaciers were melting. Notice that the atmospheric CO2 content decreases during ice ages. Click on the image for more information.
A consensus has emerged among scientists and scientific organizations worldwide that as a result of the interaction of greenhouse gases with other factors controlling the earth's temperature, global temperatures have risen, and we can expect them to continue to rise into the foreseeable future. This will be discussed under the section on "Radiation Balance".
Minor (Trace) Gases:
Neon
Noble gas; chemically unreactive.
----------------------------------
Helium
Noble gas; chemically unreactive.
----------------------------------
Methane
On left: overall change from 0 to 2000CE. On right: change just from 1984 to 2017.
(Note that the vertical axis STARTS on the right at 600 ppb and ends at 1800 ppb, so the increase from 0 to 2000CE is around 3x rather 10x as it looks. Still a very significant increase. From https://www.pnas.org/content/116/8/2805)
The increase in Methane seen here beginning with the Industrial Revolution is due to the planetary rise in human population as improvements in medical sciences and agriculture have enabled both longer life spans and more people.
Methane is one of a group of gases known as Greenhouse Gases. These are gases that absorb infrared light. The gas molecules that absorb that energy warm up, and re-radiate that heat in all directions, including back down to the Earth. Although there is relatively little methane in the atmosphere compared to other greenhouse gases like CO2 and H2O, it is a very effective absorber of infrared light. Gram for gram, it is 25 times more effective than CO2.
This will be discussed under the section on "Radiation Balance".
Krypton
Noble gas; chemically unreactive.
----------------------------------
Hydrogen
----------------------------------
Water
Water is the single most variable component of the atmosphere, varying from nearly 0 to as much as 4% by weight. The percentages of atmospheric gases quoted in the table in the previous web page are for "dry" air; i.e. without water.
I have an entire web page discussing water vapor in the atmosphere, if you are interested in going into this in more detail. It will be covered in ESC1000, but not in OCE1001, so if you are taking Oceanography you do not have to read it.
Pollutant Gases:
Carbon Monoxide
Unlike CO2, CO is extremely toxic. It combines with hemoglobin in blood much more strongly than O2, so if you breath even small amounts of CO in, hemoglobin cannot transfer the oxygen your cells (especially brain cells) need, they are starved of oxygen, and you die. This is why it is so important to not run a car in an enclosed area like a garage with the doors closed, and why running a kerosene heater indoors is so dangerous. Over 400 people die EVERY year in the US from carbon monoxide poisoning, and thousands more wind up in emergency rooms. Please be very careful when you are dealing with autos and combustible materials indoors.
One of the primary purposes of "catalytic converters" in automobile exhaust systems is to convert the CO into CO2.
----------------------------------
Ammonia
Ammonia [NH3] and nitrous oxides react with water in the atmosphere to produce nitric acid, which is one of the two main components of acid rain. As a result, there are strong incentives for countries to reduce their nitrogen-bearing emissions.
----------------------------------
Nitrous Oxides
Besides being a contributor to acid rain, some nitrous oxides (combinations of nitrogen and oxygen) are also potent greenhouse gases. In particular, N2O is, gram for gram, around 300x more effective than CO2. However, there is less than 1/1000 as much N2O as there is CO2, so the effect is smaller.
----------------------------------
Sulfur Dioxide
Sulfur dioxide is important in the atmosphere for 2 reasons. First, like the nitrogen compounds above, SO2 reacts with water in the atmosphere to produce sulfuric acid, which is the other main component of acid rain. Second, SO2 is an anti-greenhouse gas, and reflects sunlight. Because volcanic eruptions commonly emit SO2, large volcanic eruptions at times have caused significant global cooling.
The asteroid impact 65 million years ago in the Yucatan Peninsula vaporized sulfur-rich carbonate sediments, causing a series of changes - global cooling caused by the SO2 , followed by acid rain, and eventually probably global warming due to huge amounts of CO2 from the carbonate sediments. That combination of events not only caused the extinction of the dinosaurs, but many other terrestrial and marine organisms.
Injection of SO2 into the stratosphere has been suggested because of the anti-greenhouse effect of SO2.
----------------------------------
ChloroFluoroCarbons
ChloroFluoroCarbons (AKA "Freon") are a family of commercially valuable manufactured chemicals. They were used as refrigerants and as aerosol propellants because they are non-toxic, stable, and have good thermodynamic properties. Unfortunately, as is described in the Atmosphere web page, they also catalytically destroy Ozone molecules in the stratosphere, and as a result they have caused significant damage to the Ozone Layer which protects us from UV light from the Sun.
Because of the fact that CFCs destroy ozone, an international agreement, the "Montreal Protocol" was enacted in 1987 and begun in 1989, which banned the production of CFCs worldwide. The damage to the Ozone Layer is now being seen to be healed, and we can look forward to at time in the future where the Ozone Layer will be back to its pre-1980 level in another 30-50 years.