"By mole fraction (i.e., by number of molecules), dry air contains 78.08% nitrogen, 20.95% oxygen, 0.93% argon, 0.04% carbon dioxide, and small amounts of other gases."
Understanding the fundamental constituents of the Earth's atmosphere, including gases, liquids and aerosols.
Introduction to Atmospheric Chemistry: This topic covers the basics of atmospheric chemistry, including the composition of the atmosphere, the main sources and sinks of atmospheric chemicals, and the types of atmospheric reactions that take place.
Gases in the Atmosphere: This topic covers the different types of gases that are found in the atmosphere, including the major components (e.g., nitrogen, oxygen, and argon) and trace gases (e.g., carbon dioxide, methane, and ozone).
Air Pollution: This topic covers the different types of air pollution, including primary pollutants (e.g., carbon monoxide and sulfur dioxide) and secondary pollutants (e.g., ozone and particulate matter).
Atmospheric Aerosols: This topic covers the different types of atmospheric aerosols, including natural aerosols (e.g., dust and sea spray) and anthropogenic aerosols (e.g., soot and sulfuric acid).
Atmospheric Photochemistry: This topic covers the role of sunlight in atmospheric chemistry, including the mechanisms of photodissociation, photolysis, and photochemical reactions.
Stratospheric Ozone: This topic covers the chemistry of ozone in the stratosphere, including the formation and depletion of the ozone layer and the effects of ozone depletion on human health and the environment.
Tropospheric Ozone: This topic covers the chemistry of ozone in the troposphere, including its sources and sinks, formation mechanisms, and effects on human health and the environment.
Acid Rain: This topic covers the chemistry of acid rain, including the sources of acid rain precursors (e.g., sulfur dioxide and nitrogen oxides), the formation of acid rain, and the effects of acid rain on the environment.
Greenhouse Gases: This topic covers the different types of greenhouse gases, including carbon dioxide, methane, and water vapor, and their role in climate change.
Climate Change: This topic covers the science of climate change, including the evidence for global warming, the mechanisms driving climate change, and the potential impacts of climate change on human societies and the natural environment.
Nitrogen (N2): Makes up about 78% of the atmosphere. It is an essential component of amino acids, which comprise the building blocks of life.
Oxygen (O2): Makes up about 21% of the atmosphere. It is essential for respiration, combustion, and many other chemical reactions.
Argon (Ar): Makes up about 0.9% of the atmosphere. It is inert and does not react with other elements or compounds.
Carbon dioxide (CO2): Makes up about 0.04% of the atmosphere. It is a greenhouse gas that helps to regulate the temperature of the planet.
Neon (Ne): Makes up about 0.0018% of the atmosphere. It is inert and does not react with other elements or compounds.
Helium (He): Makes up about 0.00052% of the atmosphere. It is inert and does not react with other elements or compounds.
Methane (CH4): Makes up about 0.00018% of the atmosphere. It is a powerful greenhouse gas that is produced by human activities such as agriculture and fossil fuel extraction.
Hydrogen (H2): Makes up about 0.00005% of the atmosphere. It is the lightest and most abundant element in the universe.
Ozone (O3): Makes up about 0.000004% of the atmosphere. It is a reactive form of oxygen that helps to protect the planet from harmful ultraviolet radiation.
Water vapor (H2O): Makes up about 0.25% of the atmosphere in the form of invisible gas. It is essential for life and is also the most potent greenhouse gas.
Trace gases: These include various gases found in very small amounts in the atmosphere, such as helium, neon, krypton, xenon, hydrogen, and others. They are important in atmospheric chemistry and interactions with solar energy.
"The atmosphere of Earth creates pressure, absorbs most meteoroids and ultraviolet solar radiation, warms the surface through heat retention (greenhouse effect), allowing life and liquid water to exist on the Earth's surface, and reduces temperature extremes between day and night."
"Air also contains a variable amount of water vapor, on average around 1% at sea level, and 0.4% over the entire atmosphere."
"Air composition, temperature, and atmospheric pressure vary with altitude."
"Within the atmosphere, air suitable for use in photosynthesis by terrestrial plants and breathing of terrestrial animals is found only in Earth's troposphere."
"The atmosphere changed significantly over time, affected by many factors such as volcanism, life, and weathering."
"Recently, human activity has also contributed to atmospheric changes, such as global warming, ozone depletion and acid deposition."
"The atmosphere has a mass of about 5.15×10^18 kg."
"Three quarters of the atmosphere's mass is within about 11 km (6.8 mi; 36,000 ft) of the surface."
"The atmosphere becomes thinner with increasing altitude, with no definite boundary between the atmosphere and outer space."
"The Kármán line, at 100 km (62 mi) or 1.57% of Earth's radius, is often used as the border between the atmosphere and outer space."
"Atmospheric effects become noticeable during atmospheric reentry of spacecraft at an altitude of around 120 km (75 mi)."
"Several layers can be distinguished in the atmosphere, based on characteristics such as temperature and composition."
"The study of Earth's atmosphere and its processes is called atmospheric science (aerology)."
"Early pioneers in the field include Léon Teisserenc de Bort and Richard Assmann."
"Atmospheric science includes multiple subfields, such as climatology and atmospheric physics."
"The study of historic atmosphere is called paleoclimatology."
"The atmosphere [...] reduces temperature extremes between day and night (the diurnal temperature variation)."
"The atmosphere of Earth creates [...] absorbs most meteoroids and ultraviolet solar radiation."
"The atmosphere of Earth creates [...] allowing life and liquid water to exist on the Earth's surface."