Chemistry plays an influential role in the behavior of the lowest layer of Earth's atmosphere, the troposphere. The various gases in the troposphere are constantly mixing with and reacting with each other. Gases released by the oceans, emitted by living creatures, and poured into the atmosphere by human activities continually alter the balance of atmospheric chemistry.
Earth's atmosphere consists of about 78% nitrogen, 20% oxygen, and a mixture of small amounts of numerous other ingredients. Some of the minor constituents do, however, have big impacts. For example, greenhouse gases such as carbon dioxide and methane exert a large influence on the temperature of our planet.
The activities of humans play an increasingly important role in tropospheric chemistry. Fossil fuel burning generates sulfur oxides, which create sulfuric acid - a component of acid rain. Exhaust gases from cars and trucks produce nitrogen oxides, which contribute to the formation of smog and of nitric acid - another component of acid rain.
Nature also does its share to alter the chemistry of the troposphere. Volcanic eruptions, wildfires, lightning, and UV radiation from the Sun all add materials to the troposphere or chemically alter those already there. The oceans and the biosphere exchange vast quantities of gases with the atmosphere's lowest layer. The Carbon and Nitrogen Cycles play key roles in these processes.
The table below describes some of the chemical compounds that play important roles in the chemistry of Earth's troposphere. It also lists some of the processes that transform those chemicals.
|Chemical Compound||Formula||Role in Tropospheric Chemistry|
|Carbon dioxide in the troposphere is produced by photosynthesis by plants and microbes, by decomposition of organic matter, and by fossil fuel combustion. CO2 is an important greenhouse gas.|
Carbon monoxide comes from wildfires, volcanoes, and incomplete combustion in the exhaust gases from cars and trucks. It is poisonous and can help raise the levels of greenhouse gases via certain chemical reactions. It reacts with oxygen to transform into carbon dioxide.
|Hydrocarbons are released by the combustion of fossil fuels. They are one of the constituents of smog. Hydrocarbons are combinations of hydrogen and carbon atoms.|
|Hydrogen peroxide, often present in small quantities in water droplets in the atmosphere, helps create the sulfuric acid in acid rain via reactions with sulfur dioxide.|
|Methane is a powerful greenhouse gas. Although its concentration in the atmosphere is small, it has a substantial impact on Earth's energy balance.|
|78% of the gas molecules in the troposphere are nitrogen. Nitrogen atoms move through the environment via the nitrogen cycle. Hot combustion, such as in auto exhausts, incorporates nitrogen into nitrogen oxides.|
NO & NO2
|Nitrogen oxides form during high-temperature combustion in air, such as in automobile exhausts. They help to form smog and mix with water to create nitric acid, a component of acid rain.|
|Nitrogen oxides from pollutants such as car exhaust mix with water to form nitric acid. It is a component of acid rain.|
|Oxygen & Ozone||
O2 & O3
|About 20% of the gas molecules in the troposphere are oxygen. Although ozone in the stratosphere is good and protects us from UV radiation, ozone in the troposphere is bad and is a health hazard that contributes to the formation of smog.|
|PAN (Peroxyacytyl nitrate)||
|Smog was originally a term for a mixture of smoke and fog. Photochemical smog is a toxic "soup" of atmospheric pollutants often found in urban areas. It consists of nitrogen oxides, ozone, VOCs, and PAN.|
|When molecular bonds break due to energy from a collision with a solar photon.|
SO2 & SO3
|Sulfur dioxide and sulfur trioxide are produced by coal and oil burning, volcanoes, and other human and natural sources. Sulfur dioxide combines with water droplets in the air to form sulfuric acid, a component of acid rain.|
|Sulfur dioxide gas from coal and oil burning, volcanoes, and other human and natural sources, combines with water droplets in the air (and the traces of hydrogen peroxide such droplets often contain) to form sulfuric acid - which is a component of acid rain.|
Air Pollution Sources
Ozone in the Troposphere
When you think of chemistry, do you think about mixing colored liquids in test tubes and maybe making an explosion... or at least a nice puff of smoke? Did you know that a lot of chemistry happens in Earth's atmosphere? There are many different kinds of chemicals in the air. Those chemicals often combine with each other in chemical reactions, making new and different chemicals. This is called "atmospheric chemistry".
Most of the gas in our atmosphere is nitrogen. About 4/5ths of the air is nitrogen. What about the other 1/5th? Almost all of it is oxygen, the stuff in the air we need to breathe. There are also very small amounts of a bunch of other chemicals.
Have you heard of greenhouse gases? They are kinds of gases that trap the heat from sunlight in our atmosphere. Earth would be very cold if we didn't have any greenhouse gases. Carbon dioxide and methane are two very important greenhouse gases.
Some of the chemicals in the air come from pollution. When we burn coal in a factory or gasoline in our cars, we make air pollution. Coal and oil have sulfur in them. When they burn, they make chemicals called sulfur oxides. These can turn into sulfuric acid when they mix with water droplets in the air. These droplets of acid can fall to the ground as acid rain. Cars and trucks also give off chemicals called nitrogen oxides. Nitrogen oxides combine with other chemicals to make smog. They also help make nitric acid, which is another acid in acid rain.
Nature also does things to change the chemistry of the troposphere. Volcanoes, lightning, and wildfires all add chemicals to the air or change the ones that are already there. Energy from sunlight can make chemical reactions happen, changing one gas into another. Some chemicals move in cycles between the atmosphere, living creatures, and the oceans. The Carbon Cycle and the Nitrogen Cycles are two important cycles that change the chemistry of the atmosphere.
This table (below) describes some of the chemicals in the troposphere, and some of the chemical reactions that happen in the air:
Atmospheric Chemistry of Earth's Troposphere