Air

 AirBasic facts:

– the name comes from a Greek word that refers to mixing
– the atmosphere of Earth is a layer of gases surrounding the planet Earth that is retained by Earth’s gravity. The atmosphere protects life on Earth by absorbing ultraviolet solar radiation, warming the surface through heat retention (greenhouse effect), and reducing temperature extremes between day and night (the diurnal temperature variation)
– air is the name given to the atmosphere used in breathing and photosynthesis
– atmosphere is the buffer that keeps us from being peppered by meteorites, a screen against deadly radiation, and the reason radio waves can be bounced for long distances around the planet.
– dry air contains roughly (by volume) 78.09% nitrogen, 20.95% oxygen, 0.93% argon, 0.039% carbon dioxide, and small amounts of other gases
– main layers are: exosphere, thermosphere, mesosphere, stratosphere and troposphere
– above the mesosphere is the ionosphere. It extends to about 430 miles (690 kilometers) and is so thin it’s generally considered part of outer space
– tornadoes have been observed on every continent except Antarctica
– most tornadoes have wind speeds less than 110 miles per hour (177 km/h), are about 250 feet (76 m) across, and travel a few miles (several kilometers) before dissipating. The most extreme tornadoes can attain wind speeds of more than 300 miles per hour (483 km/h), stretch more than two miles (3.2 km) across, and stay on the ground for dozens of miles (more than 100 km)

Ozone layer:

– the ozone layer is a layer in Earth’s atmosphere containing relatively high concentrations of ozone (O3)
– the ozone layer was discovered in 1913 by the French physicists Charles Fabry and Henri Buisson
– the ozone layer is mainly found in the lower portion of the stratosphere from approximately 20 to 30 kilometres (12 to 19 mi) above Earth, though the thickness varies seasonally and geographically
– the layer absorbs 97–99% of the Sun’s medium-frequency ultraviolet light (from about 200 nm to 315 nm wavelength), which potentially damages exposed life forms on Earth
– ozone in the Earth’s stratosphere is created by ultraviolet light striking oxygen molecules containing two oxygen atoms (O2), splitting them into individual oxygen atoms (atomic oxygen); the atomic oxygen then combines with unbroken O2 to create ozone, O3
– the ozone layer is higher in altitude in the tropics, and lower in altitude in the extratropics, especially in the polar regions

Air pollutionAir pollution:

– China’s smog taints economy and the health of population. The country is home to seven of the world’s 10 dirtiest cities.
– air pollution can cause discomfort, disease, or death to humans, damage other living organisms such as food crops, or damage the natural environment or built environment
– major primary pollutants are produced by human activity (sulfur oxides, nitrogen oxides, carbon monoxide, carbon dioxide, volatile organic compouds, artificial particulates, persistent free radicals, toxic metals, chlorofluorocarbons, ammonia, odors, radioactiviy etc)
– there are also natural pollutans like dust, methane produced by animals, gases in Earth’s crust, natural smoke, volcanin activity etc
– classic smog results from large amounts of coal burning in an area caused by a mixture of smoke and sulfur dioxide. Modern smog does not usually come from coal but from vehicular and industrial emissions that are acted on in the atmosphere by ultraviolet light from the sun to form secondary pollutants that also combine with the primary emissions to form photochemical smog
– ground level ozone formed from NOx and VOCs. Ozone is a key constituent of the troposphere. It is also an important constituent of certain regions of the stratosphere commonly known as the Ozone layer