Nitrogen (N2) is the most abundant gas in Earth's atmosphere, including the troposphere. This cartoon also depicts several other tropospheric gases, including oxygen (O2), carbon dioxide (CO2), water vapor (H2O), methane (CH4), sulfur dioxide (SO2), and carbon monoxide (CO).
Click on image for full size
Image courtesy UCAR, modified by Windows to the Universe staff (Randy Russell).

Atmospheric Chemistry of Earth's Troposphere

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
CO2
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
CO

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
CxOy
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
H2O2
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
CH4
Methane is a powerful greenhouse gas. Although its concentration in the atmosphere is small, it has a substantial impact on Earth's energy balance.
Nitrogen
N2
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.
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.
Nitric Acid
HNO3
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)
C2H3O5N

PAN is a noxious and irritating component of smog. It forms in a reaction involving nitrogen dioxide, oxygen, and substances derived from Volatile Organic Compounds (VOCs).

Photochemical smog
-
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.
Photodissociation
-
When molecular bonds break due to energy from a collision with a solar photon.
Sulfur Oxides
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.
Sulfuric Acid
H2SO4
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.

Last modified February 7, 2006 by Randy Russell.

Shop Windows to the Universe Science Store!

Cool It! is the new card game from the Union of Concerned Scientists that teaches kids about the choices we have when it comes to climate change—and how policy and technology decisions made today will matter. Cool It! is available in our online store.

Windows to the Universe Community

News

Opportunities

You might also be interested in:

Cool It! Game

Check out our online store - minerals, fossils, books, activities, jewelry, and household items!...more

Nitrogen

Nitrogen is a chemical element with an atomic number of 7 (it has seven protons in its nucleus). Molecular nitrogen (N2) is a very common chemical compound in which two nitrogen atoms are tightly bound...more

Oxygen

Oxygen is a chemical element with an atomic number of 8 (it has eight protons in its nucleus). Oxygen forms a chemical compound (O2) of two atoms which is a colorless gas at normal temperatures and pressures....more

Earth's Greenhouse Gases

Less than 1% of the gases in Earth's atmosphere are called greenhouse gases. Even though they are not very abundant, these greenhouse gases have a major effect. Carbon dioxide (CO2), water vapor (H2O),...more

Carbon Dioxide - CO2

Carbon dioxide is a colorless and non-flammable gas at normal temperature and pressure. Although much less abundant than nitrogen and oxygen in Earth's atmosphere, carbon dioxide is an important constituent...more

Methane - CH4

Methane is gas that is found in small quantities in Earth's atmosphere. Methane is the simplest hydrocarbon, consisting of one carbon atom and four hydrogen atoms. Methane is a powerful greenhouse gas....more

Air Pollution Sources

Air pollution comes from many different sources. Natural processes that affect air quality include volcanic activity, which produce sulfur, chlorine, and ash particulates, and wildfires, which produce...more

Sulfuric Acid - H2SO4

Sulfuric acid is a viscous, oily liquid and a strong acid which can cause severe burns. Sulfuric acid consists of sulfur, oxygen, and hydrogen atoms. Sulfuric acid is one of the components of acid rain....more

Windows to the Universe, a project of the National Earth Science Teachers Association, is sponsored in part is sponsored in part through grants from federal agencies (NASA and NOAA), and partnerships with affiliated organizations, including the American Geophysical Union, the Howard Hughes Medical Institute, the Earth System Information Partnership, the American Meteorological Society, the National Center for Science Education, and TERC. The American Geophysical Union and the American Geosciences Institute are Windows to the Universe Founding Partners. NESTA welcomes new Institutional Affiliates in support of our ongoing programs, as well as collaborations on new projects. Contact NESTA for more information. NASA ESIP NCSE HHMI AGU AGI AMS NOAA