Carbon dioxide (chemical formula CO2) is a naturally occurring chemical compound composed of 2 oxygen atoms each covalently double bonded to a single carbon atom. It is a gas at standard temperature and pressure and exists in Earth's atmosphere in this state, as a trace gas at a concentration of 0.039 per cent by volume. The environmental effects of carbon dioxide are of significant interest. Atmospheric carbon dioxide is the primary source of carbon in life on Earth and its concentration in Earth's pre-industrial atmosphere since late in the Precambrian eon was regulated by photosynthetic organisms. Carbon dioxide is an important greenhouse gas; burning of carbon-based fuels since the industrial revolution has rapidly increased the concentration, leading to global warming. History Chemical and physical properties Structure and bonding The carbon dioxide molecule is linear and centrosymmetric. In aqueous solution The hydration equilibrium constant of carbonic acid is (at 25 °C). . Uses
Related: Earth's Atmosphere
Greenhouse gasSince the beginning of the Industrial Revolution (taken as the year 1750), the burning of fossil fuels and extensive clearing of native forests has contributed to a 40% increase in the atmospheric concentration of carbon dioxide, from 280 ppm in 1750 to 392.6 ppm in 2012. It has now reached 400 ppm in the northern hemisphere. In the Solar System, the atmospheres of Venus, Mars, and Titan also contain gases that cause a greenhouse effect, though Titan's atmosphere has an anti-greenhouse effect that reduces the warming. Gases in Earth's atmosphere Greenhouse gases Greenhouse gases are those that can absorb and emit infrared radiation, but not radiation in or near the visible spectrum. Non-greenhouse gases Although contributing to many other physical and chemical reactions, the major atmospheric constituents, nitrogen (N 2), oxygen (O 2), and argon (Ar), are not greenhouse gases. Indirect radiative effects Impacts on the overall greenhouse effect
OzoneOzone /ˈoʊzoʊn/ (systematically named 1λ1,3λ1-trioxidane and μ-oxidodioxygen), or trioxygen, is an inorganic molecule with the chemical formula O 3(μ-O) (also written [O(μ-O)O] or O 3). It is a pale blue gas with a distinctively pungent smell. It is an allotrope of oxygen that is much less stable than the diatomic allotrope O 2, breaking down in the lower atmosphere to normal dioxygen. Ozone is formed from dioxygen by the action of ultraviolet light and also atmospheric electrical discharges, and is present in low concentrations throughout the Earth's atmosphere. In total, ozone makes up only 0.6 ppm of the atmosphere. Ozone's odor is sharp, reminiscent of chlorine, and detectable by many people at concentrations of as little as 10 ppb in air. Ozone is a powerful oxidant (far more so than dioxygen) and has many industrial and consumer applications related to oxidation. Nomenclature The trivial name ozone is the most commonly used and preferred IUPAC name. History  
PhotosynthesisSchematic of photosynthesis in plants. The carbohydrates produced are stored in or used by the plant. Overall equation for the type of photosynthesis that occurs in plants Composite image showing the global distribution of photosynthesis, including both oceanic phytoplankton and terrestrial vegetation. Dark red and blue-green indicate regions of high photosynthetic activity in ocean and land respectively. Photosynthesis is a process used by plants and other organisms to convert light energy, normally from the sun, into chemical energy that can be later released to fuel the organisms' activities. Although photosynthesis is performed differently by different species, the process always begins when energy from light is absorbed by proteins called reaction centres that contain green chlorophyll pigments. Overview Photosynthesis changes sunlight into chemical energy, splits water to liberate O2, and fixes CO2 into sugar. The general equation for photosynthesis is therefore: Z scheme The "Z scheme"
OxygenBlue white glow from an oxygen discharge tube. Oxygen is an important part of the atmosphere, and is necessary to sustain most terrestrial life as it is used in respiration. However, it is too chemically reactive to remain a free element in Earth's atmosphere without being continuously replenished by the photosynthetic action of living organisms, which use the energy of sunlight to produce elemental oxygen from water. Oxygen was discovered independently by Carl Wilhelm Scheele, in Uppsala, in 1773 or earlier, and Joseph Priestley in Wiltshire, in 1774, but Priestley is often given priority because his work was published first. Characteristics Structure Oxygen O2 molecule. At standard temperature and pressure, oxygen is a colorless, odorless gas with the molecular formula O 2, in which the two oxygen atoms are chemically bonded to each other with a spin triplet electron configuration. A trickle of liquid oxygen is deflected by a magnetic field, illustrating its paramagnetic property
Earth's Atmosphere Layer 5: ExosphereEarth atmosphere diagram showing the exosphere and other layers. The layers are to scale. From Earth's surface to the top of the stratosphere (50km) is just under 1% of Earth's radius. The exosphere (Ancient Greek: ἔξω éxō "outside, external, beyond", Ancient Greek: σφαῖρα sphaĩra "sphere") is a thin, atmosphere-like volume surrounding a planetary body where molecules are gravitationally bound to that body, but where the density is too low for them to behave as a gas by colliding with each other. In the case of bodies with substantial atmospheres, such as the Earth's atmosphere, the exosphere is the uppermost layer, where the atmosphere thins out and merges with interplanetary space. Several moons, such as Earth's moon and the Galilean satellites, have exospheres without a denser atmosphere underneath. Earth's exosphere Lower boundary The exobase can be defined in one of two ways: and height equal to the mean free path , at pressure and temperature . where Upper boundary
Earth's Atmosphere Layer 4: ThermosphereEarth atmosphere diagram showing the exosphere and other layers. The layers are to scale. From Earth's surface to the top of the stratosphere (50 kilometres (31 mi)) is just under 1% of Earth's radius. The thermosphere is the layer of the Earth's atmosphere directly above the mesosphere and directly below the exosphere. The highly diluted gas in this layer can reach 2,500 °C (4,530 °F) during the day. The dynamics of the thermosphere are dominated by atmospheric tides, which are driven by the very significant diurnal heating. Neutral gas constituents It is convenient to separate the atmospheric regions according to the two temperature minima at about 12 km altitude (the tropopause) and at about 85 km (the mesopause) (Figure 1). Figure 1. The density of the Earth's atmosphere decreases nearly exponentially with altitude. Turbulence causes the air within the lower atmospheric regions below the turbopause at about 110 km to be a mixture of gases that does not change its composition.
Earth's Atmosphere Layer 3: MesosphereSpace Shuttle Endeavour appears to straddle the stratosphere and mesosphere in this photo. "The orange layer is the troposphere, where all of the weather and clouds which we typically watch and experience are generated and contained. This orange layer gives way to the whitish Stratosphere and then into the Mesosphere. Earth atmosphere diagram showing the exosphere and other layers. The mesosphere (/ˈmɛsoʊsfɪər/; from Greek mesos "middle" and sphaira "ball") is the layer of the Earth's atmosphere that is directly above the stratopause and directly below the mesopause. The stratosphere, mesosphere and lowest part of the thermosphere are collectively referred to as the "middle atmosphere", which spans heights from approximately 10 kilometres (33,000 ft) to 100 kilometres (62 mi). Temperature Within the mesosphere, temperature decreases with increasing altitude. Dynamic features Noctilucent clouds are located in the mesosphere. Uncertainties Meteors References
Earth's Atmosphere Layer 2: StratosphereSpace Shuttle Endeavour appears to straddle the stratosphere and mesosphere in this photo. "The orange layer is the troposphere, where all of the weather and clouds which we typically watch and experience are generated and contained. This orange layer gives way to the whitish Stratosphere and then into the Mesosphere. Atmosphere diagram showing stratosphere. This image shows the temperature trend in the Lower Stratosphere as measured by a series of satellite-based instruments between January 1979 and December 2005. The stratosphere /ˈstrætəsfɪər/ is the second major layer of Earth's atmosphere, just above the troposphere, and below the mesosphere. Ozone and temperature Methane, (CH4) while not a direct cause of ozone destruction in the stratosphere, does lead to the formation of compounds that destroy ozone. Aircraft flight Concorde would cruise at mach 2 at about 18,000 m (59,000 ft), and the SR-71 would cruise at mach 3 at 26,000 m (85,000 ft), all still in the stratosphere.