Gulf Air (Arabic: طيران الخليج‎ Ṭayarān al-Khalīj) is the principal flag carrier of the Kingdom of Bahrain. Headquartered in Muharraq,^[1] adjacent to Bahrain International Airport,^[2] the airline operates scheduled services to 41 destinations in 30 countries across Africa, Asia and Europe. Its main base is Bahrain International Airport.^[3] and major destinations include London, Paris, Rome, Frankfurt, Dubai, Karachi, and Mumbai.

The airline is part of the Oneworld global explorer fare. It has extensive codeshare agreements with other airlines and special partnerships with Jet Airways and Oman Air's Frequent Flyer Programmes.

History[link]

1940–1973: Persian Gulf[link]

A Gulf Air Vickers VC-10 landing at London Heathrow Airport. (1977)

In the late 1940s, Freddie Bosworth, a British pilot and entrepreneur, began an air taxi service to Doha and Dhahran from Bahrain. Bosworth later expanded service and, in 1950, registered Gulf Aviation as a private shareholding company, making it one of the oldest carriers in the Middle East.^[4] The fleet contained seven Avro Ansons and three De Havilland DH.86B 4-engine biplanes.

In October 1951, British Overseas Airways Corporation (BOAC) became a major shareholder in Gulf Aviation, holding a 22% stake.^[3]

1970s: Joint Ownership[link]

In 1973 the governments of the Kingdom of Bahrain, State of Qatar, the Emirate of Abu Dhabi, and the Sultanate of Oman purchased BOAC's shares in Gulf Aviation. The Foundation Treaty signed on 1 January 1974 gave each government a 25% shareholding in the rebranded Gulf Air, which became the flag carrier for the four states. Later that year, the airline's support of oil exploration resulted in the establishment of the wholly owned subsidiary Gulf Helicopters.^[3]

Boeing 747-200 of Gulf Air at CDG in 1986.

With leased Lockheed L-1011 Tristar and Boeing 737 aircraft joining the fleet, by 1976, Gulf Air had expanded its route network to include Amman, Amsterdam, Athens, Baghdad, Bombay, Bangkok, Beirut, Cairo, Colombo, Delhi, Dhaka, Hong Kong, Jeddah, Karachi, Khartoum, Larnaca, Manila, Paris, Ras al-Khaimah and San‘a’. The fleet comprised four Vickers VC10, three BAC One-Elevens, two Lockheed L-1011 Tristar 200s, and five Boeing 737–200s. Two years later, the airline doubled the Tristar fleet by replacing the VC10s. Meanwhile, the airline increased the Boeing 737 fleet to nine and phased out the One-Elevens.

1980s–1992: Expansion[link]

The 1980s saw an increase in air travel and growth for Gulf Air. In 1981 Gulf Air became an IATA member and in the following year became the first international airline to land at Riyadh. In 1985, Emirates, the national startup and national carrier of Dubai, United Arab Emirates began operating, which would later become a major rival of Gulf Air. In 1988 the Boeing 767s joined the fleet and the airline launched service to Frankfurt, Istanbul, Damascus, Dar es Salaam, Fujairah, and Nairobi, and resumed service to Shiraz, and Baghdad.

Gulf Air celebrated its 40th anniversary in 1990. The light blue and peach Balenciaga-designed uniform was introduced. Singapore, Sydney, and Thiruvananthapuram were launched and Gulf Air became the first Arab airline to fly to Australia. Gulf Air added service to Johannesburg and Melbourne in 1992, becoming the first Arab airline to fly directly to these cities. In 1993, it opened up a flight simulator centre in Qatar, and introduced service to Casablanca, Entebbe, Jakarta, Kilimanjaro, Madras, Rome, San'a', Zanzibar, and Zürich.

1993–2005: New livery & destinations[link]

A Gulf Air Airbus A340-312 taxiing at London Heathrow Airport. (2005)

In May 1994, Gulf Air received its first Airbus A340-300. Gulf Air introduced a no-smoking policy on flights to Singapore and Australia in 1998, which the airline later extended through its whole network. In 1999, Gulf Air launched three new routes in northern Pakistan—Islamabad, Lahore, and Peshawar. It also took delivery of two out of six Airbus A330-200 aircraft, and introduced a new Balmain uniform.^{[citation needed]} The Gulf Air website opened in January 1997.^[5]

In 2000 the airline celebrated its 50th anniversary. It took delivery of the remaining Airbus A330-200 aircraft in June of that year, and launched service to Milan. In May 2002, James Hogan became President and CEO of Gulf Air and instigated a three-year restructuring and turnaround programme, which was launched in response to a drastic fall in profits at the company and increasing debt. The Gulf Air board unanimously approved the three-year recovery plan at the extraordinary general meeting held on 18 December.^{[citation needed]} By 1 August 2002 the State of Qatar announced intentions to withdraw from Gulf Air. The state remained a member state for a six month period after announcing the intention to withdraw.^[6]

In 2003 Gulf Air introduced a new Landor Associates designed livery. 1 June 2003 saw the establishment of Gulf Traveller, a subsidiary all-economy full-service airline. Gulf Air also announced a sponsorship deal for the Bahrain Grand Prix through 2010, creating the Gulfair Bahrain Grand Prix, of which the first was staged in 2004. Gulf Air also introduced direct daily flights to Athens and Sydney, via Singapore on 23 November 2003.

A Gulf Air Airbus A340-312 in special 50th anniversary livery. (2005)

In 2004, Gulf Air introduced direct flights between Dubai and London and Muscat and London, and a daily service between Abu Dhabi and Ras Al Khaimah and carried a record 7.5 million passengers during this year. Gulf Air's sponsorship of the Bahrain Formula 1 Grand Prix continued, with a record race crowd and a global TV audience. The airline announced a return to profit, with the best financial performance since 1997. Despite a BD30 million (US$80 million) cost to the business through fuel price rises during the year, Gulf Air recorded a profit of BD1.5 million (US$4.0 million) in the calendar year to December 2004, on revenues up 23.8% to BD476.3 million (US$1.26 billion) (2003: BD 384.6 million / USD1,020.2 million). The results meant the airline out-performed the targets set under Project Falcon, the three-year restructuring plan approved by the Board in December 2002. The owner states of Gulf Air at that time—the Kingdom of Bahrain, the Emirate of Abu Dhabi, and the Sultanate of Oman—confirmed their support for further expansion of the airline through a new three-year strategic plan which would include re-equipment of the aircraft fleet and recapitalization of the business through private sector financing. Gulf Air was also placed on the IOSA registry following its successful completion of the IATA Operational Safety Audit (IOSA).

2006–2008: Bahrain takes over[link]

A Gulf Air Airbus A330-243 departs London Heathrow Airport. (2006)

The new summer schedule commencing 28 April 2006 saw the complete withdrawal of Abu Dhabi as a hub following the decision on 13 September 2005 by the Emirate of Abu Dhabi to withdraw from Gulf Air and establish its own airline, Etihad Airways.^[4] Gulf Air changed its operations to a dual hub basis between Bahrain and Muscat airports. The airline produced a series of adverts in local newspapers thanking Abu Dhabi for its contribution to Gulf Air. Due to the airline being the national carrier for the United Arab Emirates for over 35 years, it has a large customer base located in Abu Dhabi. Gulf Air endeavoured to show the continuing support for flights to Abu Dhabi from Bahrain and Muscat, connecting to the rest of the Gulf Air network, via advertisements placed in local newspapers.

A Gulf Air Airbus A340-313 departs London Heathrow Airport. (2007)

James Hogan resigned as President and Chief Executive Officer as of 1 October 2006 and has since taken the position of CEO at rival airline Etihad. Ahmed Al Hammadi was named acting chief executive officer until Swiss national André Dosé, the former chief executive officer of Crossair and Swiss International Air Lines, began on 1 April 2007. A few days later, Dosé announced a BD310 million (USD825 million) restructuring plan that included originating or terminating all flights in Bahrain, ceasing routes to Johannesburg, Dublin, Jakarta, Singapore, Hong Kong and Sydney; eliminating nine Boeing 767s from the fleet, phasing out the Airbus A340-300 from the fleet, introducing the Airbus A321 in July 2007 and the Airbus A330-300 in 2009, and terminating employees based on performance and without regard for nationality. This led to some employees applying for jobs in other airlines and, in less than a month, Gulf Air lost 500 persons from its workforce, prompting the airline to rule out mass layoffs as part of its recovery plan, except for performance reasons. The airline is aiming at cutting its workforce by 25 percent through people leaving naturally or accepting voluntary early retirement packages, and the company has a recruitment freeze.

On 6 May 2007, the government of Bahrain claimed full ownership of the airline as joint-owner Oman withdrew from the airline. André Dosé resigned on 23 July 2007 and was replaced by Bjorn Naf. On 6 November 2007, Gulf Air started its third daily nonstop flight to London Heathrow Airport from Bahrain. On the same day, Gulf Air became fully owned by Bahrain.

The airline inaugurated services to Shanghai Pudong International Airport on 16 June 2008 and has placed orders with Boeing (for 24 B787s) and Airbus (for 15 A320s and 20 A330s) to upgrade its fleet.

The airline's last commercial Boeing 767 flight was on 29 May 2008 and the aircraft was flown to Dublin on 30 May 2008; two of the Boeing 767 aircraft are now in storage at Bournemouth Airport.

On 3 July 2008, Gulf Air was announced as the official sponsor of upcoming English football club, Queens Park Rangers.

Gulf Air signed, in 2008, a lease agreement for five aircraft with International Lease Finance Corporation (ILFC) as part of the airline's growth and expansion strategy. The lease is for six years for two Airbus A319-100, delivered in September 2008, and three Airbus A330-200, due for delivery in March, April and May 2009.

2009–present: Change in the airline, new CEO[link]

A320-200 at the Bahrain Airshow

In March 2009, Gulf Air signed a 42-month lease agreement with Jet Airways for four Boeing 777-300ERs, but the aircraft were returned to Jet Airways starting in September 2009.

In May 2009, Gulf Air inaugurated summer seasonal flights to Alexandria, Aleppo and Salalah.

Starting June 2009, Gulf Air's Golden Falcon logo will be on the streets of London, emblazoned on the side of the city's taxi cabs, as part a two-year marketing deal. Fifty Hackney Carriages will be rolled out in full Gulf Air livery to promote the airline's flights from London Heathrow to Bahrain and beyond.^[7]

At the 2009 Paris Air Show, Gulf Air selected the Rolls-Royce Trent 700EP engine to power an additional 20 Airbus A330s that it is to start receiving in 2012. Rolls-Royce will provide 44 Trent 700EPs, including four spares, to the airline, which already has Trents on its 10 A330-200s in service.^[8] Later in June, the carrier announced the departure of CEO Bjorn Naf and the appointment of Samer Majali (who worked previously for Royal Jordanian) as CEO effective 1 August 2009.

On 1 September 2009, Gulf Air resumed flights to Baghdad.^[9] Service to Najaf will begin 26 September and Erbil will begin on 26 October.

Gulf Air is planning to sell 5 of their Airbus A340-300 and lease the others.^[10][11]

On 1 March 2010, Gulf Air launched its new "Falcon Gold" cabin, a single premium cabin that is aimed at offering higher standards of comfort for the standard premium price. As of August 2011, the new Flat Beds are installed on all aircraft except short haul aircraft.

Gulf Air temporarily suspended flights to Iran and Lebanon during the height of the 2011 Bahraini Uprising.

Destinations[link]

Gulf Air flies to 41 international destinations in 30 countries across Africa, Asia and Europe from its hub at Bahrain International Airport.^[12]

Codeshare agreements[link]

Gulf Air has codeshare agreements with the following airlines:

Fleet[link]

As of 28 May 2012, the Gulf Air fleet consists of the following aircraft^[13] with an average age of 7.3 years:^[14]

Last Updated By: 'MHAftab' - On Tuesday 28th May 2012.

Fleet history[link]

Over the years, Gulf Air operated the following aircraft types:^[15]

Lounges[link]

While usually providing third part lounges at their destinations, Gulf Air´s own Falcon Gold lounge could be found at the airports of Bahrain, Dubai and London–Heathrow.

Subsidiaries[link]

Gulf Traveller[link]

"Gulf Traveller" was the all-economy full service subsidiary airline of Gulf Air. Its main base was Abu Dhabi International Airport.^[3] It was briefly relocated between Bahrain and Muscat airports after Abu Dhabi pulled out of the Gulf Air consortium in 2005, and in May 2007 Oman also pulled out of the group leaving Bahrain as sole owner of Gulf Air. Gulf Traveller has since been disbanded due to these changes.

Sponsorship[link]

Gulf Air sponsors events, of which the most prestigious is the Bahrain Grand Prix. This is usually the first or fourth race of the Formula One season and is held in March or April of each year. Gulf Air were also the first ever shirt sponsors of Chelsea F.C. in 1983 and 1984.^[16] More recently, they were shirt sponsors of Queens Park Rangers F.C.; this was from 2008 to 2011.^[17]

Incidents and accidents[link]

• 23 September 1983: Gulf Air Flight 771 was a flight from Karachi, Pakistan to Qatar via Abu Dhabi, United Arab Emirates. On 23 September 1983, while the Boeing 737-2P6^[18] was on approach to Abu Dhabi International Airport, a bomb exploded in the baggage compartment. The plane crashed in the desert near Mina Jebel Ali between Abu Dhabi and Dubai in the UAE. All seven crew members and 105 passengers died. Most of the dead passengers were Pakistani nationals, many returning to jobs in the Gulf after spending the Eid ul-Adha holiday with their families in Pakistan.^[19] The bomb was apparently planted by the Abu Nidal organization, to convince the Gulf States to pay protection money to Nidal so as to avoid attacks on their soil^{[citation needed]}

• 23 August 2000: Gulf Air Flight 072 crashed into the Persian Gulf on approach to Bahrain International Airport from Cairo. The A320 with 143 passengers and crew on board approached the landing at higher speeds than normal and carried out an unusual low altitude orbit in an attempt to correct the approach.^[20][21] The orbit was unsuccessful and a go-around was attempted. While carrying out a turning climb the aircraft entered a descent at 15 degrees nose down. The aircrew did not respond to repeated GPWS warnings^[22] and approximately one minute after starting the go-around the aircraft disappeared from radar screens.^[23] There were no survivors. 36 children were on the aircraft.^[24] The accident investigation concluded that the primary cause of the crash was pilot error (including spatial disorientation), with a secondary factor being systemic organizational and oversight issues.^[25] Flight 072 was the highest death toll of any accident involving an Airbus A320 at that time. It was subsequently surpassed by TAM Airlines Flight 3054, which crashed on 17 July 2007 with 199 fatalities.

References[link]

This article includes a list of references, but its sources remain unclear because it has insufficient inline citations. Please help to improve this article by introducing more precise citations. (July 2010)

References

Bibliography

External links[link]

	Bahrain portal
	Abu Dhabi portal
	Oman portal
	Qatar portal
	Aviation portal

Wikimedia Commons has media related to: Gulf Air

• Official website

v t e Airlines of Bahrain Bahrain Air DHL International Aviation ME Gulf Air

Blue light is scattered more than other wavelengths by the gases in the atmosphere, giving the Earth a blue halo when seen from space.

Limb view, of the Earth's atmosphere. Colours roughly denote the layers of the atmosphere.

This image shows the moon at centre, with the limb of Earth near the bottom transitioning into the orange-coloured troposphere, the lowest and most dense portion of the Earth's atmosphere. The troposphere ends abruptly at the tropopause, which appears in the image as the sharp boundary between the orange- and blue- coloured atmosphere. The silvery-blue noctilucent clouds extend far above the Earth's troposphere.

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).

Atmospheric stratification describes the structure of the atmosphere, dividing it into distinct layers, each with specific characteristics such as temperature or composition. The atmosphere has a mass of about 5×10¹⁸ kg, three quarters of which is within about 11 km (6.8 mi; 36,000 ft) of the surface. The atmosphere becomes thinner and thinner with increasing altitude, with no definite boundary between the atmosphere and outer space. An altitude of 120 km (75 mi) is where atmospheric effects become noticeable during atmospheric reentry of spacecraft. The Kármán line, at 100 km (62 mi), also is often regarded as the boundary between atmosphere and outer space.

Air is the name given to atmosphere used in breathing and photosynthesis. 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. Air also contains a variable amount of water vapor, on average around 1%. While air content and atmospheric pressure vary at different layers, air suitable for the survival of terrestrial plants and terrestrial animals is currently only known to be found in Earth's troposphere and artificial atmospheres.

Composition[link]

Composition of Earth's atmosphere. The lower pie represents the trace gases which together compose 0.039% of the atmosphere. Values normalized for illustration. The numbers are from a variety of years (mainly 1987, with CO₂ and methane from 2009) and do not represent any single source.

Mean atmospheric water vapor

Air is mainly composed of nitrogen, oxygen, and argon, which together constitute the major gases of the atmosphere. The remaining gases are often referred to as trace gases,^[1] among which are the greenhouse gases such as water vapor, carbon dioxide, methane, nitrous oxide, and ozone. Filtered air includes trace amounts of many other chemical compounds. Many natural substances may be present in tiny amounts in an unfiltered air sample, including dust, pollen and spores, sea spray, and volcanic ash. Various industrial pollutants also may be present, such as chlorine (elementary or in compounds), fluorine compounds, elemental mercury, and sulfur compounds such as sulfur dioxide [SO₂].

Structure of the atmosphere[link]

Principal layers[link]

In general, air pressure and density decrease in the atmosphere as height increases. However, temperature has a more complicated profile with altitude. Because the general pattern of this profile is constant and recognizable through means such as balloon soundings, temperature provides a useful metric to distinguish between atmospheric layers. In this way, Earth's atmosphere can be divided into five main layers. From highest to lowest, these layers are:

Exosphere[link]

The outermost layer of Earth's atmosphere extends from the exobase upward. It is mainly composed of hydrogen and helium. The particles are so far apart that they can travel hundreds of kilometers without colliding with one another. Since the particles rarely collide, the atmosphere no longer behaves like a fluid. These free-moving particles follow ballistic trajectories and may migrate into and out of the magnetosphere or the solar wind.

Thermosphere[link]

Temperature increases with height in the thermosphere from the mesopause up to the thermopause, then is constant with height. Unlike in the stratosphere, where the inversion is caused by absorption of radiation by ozone, in the thermosphere the inversion is a result of the extremely low density of molecules. The temperature of this layer can rise to 1,500 °C (2,700 °F), though the gas molecules are so far apart that temperature in the usual sense is not well defined. The air is so rarefied that an individual molecule (of oxygen, for example) travels an average of 1 kilometer between collisions with other molecules.^[3] The International Space Station orbits in this layer, between 320 and 380 km (200 and 240 mi). Because of the relative infrequency of molecular collisions, air above the mesopause is poorly mixed compared to air below. While the composition from the troposphere to the mesosphere is fairly constant, above a certain point, air is poorly mixed and becomes compositionally stratified. The point dividing these two regions is known as the turbopause. The region below is the homosphere, and the region above is the heterosphere. The top of the thermosphere is the bottom of the exosphere, called the exobase. Its height varies with solar activity and ranges from about 350–800 km (220–500 mi; 1,100,000–2,600,000 ft).^{[citation needed]}

Mesosphere[link]

The mesosphere extends from the stratopause to 80–85 km (50–53 mi; 260,000–280,000 ft). It is the layer where most meteors burn up upon entering the atmosphere. Temperature decreases with height in the mesosphere. The mesopause, the temperature minimum that marks the top of the mesosphere, is the coldest place on Earth and has an average temperature around −85 °C (−120 °F; 190 K).^[4] At the mesopause, temperatures may drop to −100 °C (−150 °F; 170 K).^[5] Due to the cold temperature of the mesosphere, water vapor is frozen, forming ice clouds (or Noctilucent clouds). A type of lightning referred to as either sprites or ELVES, form many miles above thunderclouds in the troposphere.

Stratosphere[link]

The stratosphere extends from the tropopause to about 51 km (32 mi; 170,000 ft). Temperature increases with height due to increased absorption of ultraviolet radiation by the ozone layer, which restricts turbulence and mixing. While the temperature may be −60 °C (−76 °F; 210 K) at the tropopause, the top of the stratosphere is much warmer, and may be near freezing^{[citation needed]}. The stratopause, which is the boundary between the stratosphere and mesosphere, typically is at 50 to 55 km (31 to 34 mi; 160,000 to 180,000 ft). The pressure here is 1/1000 sea level.

Troposphere[link]

The troposphere begins at the surface and extends to between 9 km (30,000 ft) at the poles and 17 km (56,000 ft) at the equator,^[6] with some variation due to weather. The troposphere is mostly heated by transfer of energy from the surface, so on average the lowest part of the troposphere is warmest and temperature decreases with altitude. This promotes vertical mixing (hence the origin of its name in the Greek word "τροπή", trope, meaning turn or overturn). The troposphere contains roughly 80% of the mass of the atmosphere.^[7] The tropopause is the boundary between the troposphere and stratosphere.

Other layers[link]

Within the five principal layers determined by temperature are several layers determined by other properties:

• The ozone layer is contained within the stratosphere. In this layer ozone concentrations are about 2 to 8 parts per million, which is much higher than in the lower atmosphere but still very small compared to the main components of the atmosphere. It is mainly located in the lower portion of the stratosphere from about 15–35 km (9.3–22 mi; 49,000–110,000 ft), though the thickness varies seasonally and geographically. About 90% of the ozone in our atmosphere is contained in the stratosphere.
• The ionosphere, the part of the atmosphere that is ionized by solar radiation, stretches from 50 to 1,000 km (31 to 620 mi; 160,000 to 3,300,000 ft) and typically overlaps both the exosphere and the thermosphere. It forms the inner edge of the magnetosphere. It has practical importance because it influences, for example, radio propagation on the Earth. It is responsible for auroras.
• The homosphere and heterosphere are defined by whether the atmospheric gases are well mixed. In the homosphere the chemical composition of the atmosphere does not depend on molecular weight because the gases are mixed by turbulence.^[8] The homosphere includes the troposphere, stratosphere, and mesosphere. Above the turbopause at about 100 km (62 mi; 330,000 ft) (essentially corresponding to the mesopause), the composition varies with altitude. This is because the distance that particles can move without colliding with one another is large compared with the size of motions that cause mixing. This allows the gases to stratify by molecular weight, with the heavier ones such as oxygen and nitrogen present only near the bottom of the heterosphere. The upper part of the heterosphere is composed almost completely of hydrogen, the lightest element.
• The planetary boundary layer is the part of the troposphere that is nearest the Earth's surface and is directly affected by it, mainly through turbulent diffusion. During the day the planetary boundary layer usually is well-mixed, while at night it becomes stably stratified with weak or intermittent mixing. The depth of the planetary boundary layer ranges from as little as about 100 m on clear, calm nights to 3000 m or more during the afternoon in dry regions.

The average temperature of the atmosphere at the surface of Earth is 14 °C (57 °F; 287 K)^[9] or 15 °C (59 °F; 288 K),^[10] depending on the reference.^{[11] [12][13]}

Physical properties[link]

Comparison of the 1962 US Standard Atmosphere graph of geometric altitude against air density, pressure, the speed of sound and temperature with approximate altitudes of various objects.^[14]

Pressure and thickness[link]

The average atmospheric pressure at sea level is about 1 atmosphere (atm) = 101.3 kPa (kilopascals) = 14.7 psi (pounds per square inch) = 760 torr = 29.92 inches of mercury (symbol Hg). Total atmospheric mass is 5.1480×10¹⁸ kg (1.135×10¹⁹ lb),^[15] about 2.5% less than would be inferred from the average sea level pressure and the Earth's area of 51007.2 megahectares, this portion being displaced by the Earth's mountainous terrain. Atmospheric pressure is the total weight of the air above unit area at the point where the pressure is measured. Thus air pressure varies with location and weather.

If the atmosphere had a uniform density, it would terminate abruptly at an altitude of 8.50 km (27,900 ft). It actually decreases exponentially with altitude, dropping by half every 5.6 km (18,000 ft) or by a factor of 1/e every 7.64 km (25,100 ft), the average scale height of the atmosphere below 70 km (43 mi; 230,000 ft). However, the atmosphere is more accurately modeled with a customized equation for each layer that takes gradients of temperature, molecular composition, solar radiation and gravity into account.

In summary, the mass of the earth's atmosphere is distributed approximately as follows:^[16]

• 50% is below 5.6 km (18,000 ft).
• 90% is below 16 km (52,000 ft).
• 99.99997% is below 100 km (62 mi; 330,000 ft), the Kármán line. By international convention, this marks the beginning of space where human travelers are considered astronauts.

By comparison, the summit of Mt. Everest is at 8,848 m (29,029 ft); commercial airliners typically cruise between 10 km (33,000 ft) and 13 km (43,000 ft) where the thinner air improves fuel economy; weather balloons reach 30.4 km (100,000 ft) and above; and the highest X-15 flight in 1963 reached 108.0 km (354,300 ft).

Even above the Kármán line, significant atmospheric effects such as auroras still occur. Meteors begin to glow in this region though the larger ones may not burn up until they penetrate more deeply. The various layers of the earth's ionosphere, important to HF radio propagation, begin below 100 km and extend beyond 500 km. By comparison, the International Space Station and Space Shuttle typically orbit at 350–400 km, within the F-layer of the ionosphere where they encounter enough atmospheric drag to require reboosts every few months. Depending on solar activity, satellites can still experience noticeable atmospheric drag at altitudes as high as 700–800 km.

Density and mass[link]

Temperature and mass density against altitude from the NRLMSISE-00 standard atmosphere model (the eight dotted lines in each "decade" are at the eight cubes 8, 27, 64, ..., 729)

The density of air at sea level is about 1.2  kg/m³ (1.2 g/L). Density is not measured directly but is calculated from measurements of temperature, pressure and humidity using the equation of state for air (a form of the ideal gas law). Atmospheric density decreases as the altitude increases. This variation can be approximately modeled using the barometric formula. More sophisticated models are used to predict orbital decay of satellites.

The average mass of the atmosphere is about 5 quadrillion (5×10¹⁵) tonnes or 1/1,200,000 the mass of Earth. According to the American National Center for Atmospheric Research, "The total mean mass of the atmosphere is 5.1480×10¹⁸ kg with an annual range due to water vapor of 1.2 or 1.5×10¹⁵ kg depending on whether surface pressure or water vapor data are used; somewhat smaller than the previous estimate. The mean mass of water vapor is estimated as 1.27×10¹⁶ kg and the dry air mass as 5.1352 ±0.0003×10¹⁸ kg."

Optical properties[link]

Solar radiation (or sunlight) is the energy the Earth receives from the Sun. The Earth also emits radiation back into space, but at longer wavelengths that we cannot see. Part of the incoming and emitted radiation is absorbed or reflected by the atmosphere.

Scattering[link]

When light passes through our atmosphere, photons interact with it through scattering. If the light does not interact with the atmosphere, it is called direct radiation and is what you see if you were to look directly at the Sun. Indirect radiation is light that has been scattered in the atmosphere. For example, on an overcast day when you cannot see your shadow there is no direct radiation reaching you, it has all been scattered. As another example, due to a phenomenon called Rayleigh scattering, shorter (blue) wavelengths scatter more easily than longer (red) wavelengths. This is why the sky looks blue; you are seeing scattered blue light. This is also why sunsets are red. Because the Sun is close to the horizon, the Sun's rays pass through more atmosphere than normal to reach your eye. Much of the blue light has been scattered out, leaving the red light in a sunset.

Absorption[link]

Different molecules absorb different wavelengths of radiation. For example, O₂ and O₃ absorb almost all wavelengths shorter than 300 nanometers. Water (H₂O) absorbs many wavelengths above 700 nm. When a molecule absorbs a photon, it increases the energy of the molecule. We can think of this as heating the atmosphere, but the atmosphere also cools by emitting radiation, as discussed below.

Rough plot of Earth's atmospheric transmittance (or opacity) to various wavelengths of electromagnetic radiation, including visible light.

The combined absorption spectra of the gases in the atmosphere leave "windows" of low opacity, allowing the transmission of only certain bands of light. The optical window runs from around 300 nm (ultraviolet-C) up into the range humans can see, the visible spectrum (commonly called light), at roughly 400–700 nm and continues to the infrared to around 1100 nm. There are also infrared and radio windows that transmit some infrared and radio waves at longer wavelengths. For example, the radio window runs from about one centimeter to about eleven-meter waves.

Emission[link]

Emission is the opposite of absorption, it is when an object emits radiation. Objects tend to emit amounts and wavelengths of radiation depending on their "black body" emission curves, therefore hotter objects tend to emit more radiation, with shorter wavelengths. Colder objects emit less radiation, with longer wavelengths. For example, the Sun is approximately 6,000 K (5,730 °C; 10,340 °F), its radiation peaks near 500 nm, and is visible to the human eye. The Earth is approximately 290 K (17 °C; 62 °F), so its radiation peaks near 10,000 nm, and is much too long to be visible to humans.

Because of its temperature, the atmosphere emits infrared radiation. For example, on clear nights the Earth's surface cools down faster than on cloudy nights. This is because clouds (H₂O) are strong absorbers and emitters of infrared radiation. This is also why it becomes colder at night at higher elevations. The atmosphere acts as a "blanket" to limit the amount of radiation the Earth loses into space.

The greenhouse effect is directly related to this absorption and emission (or "blanket") effect. Some chemicals in the atmosphere absorb and emit infrared radiation, but do not interact with sunlight in the visible spectrum. Common examples of these chemicals are CO₂ and H₂O. If there are too much of these greenhouse gases, sunlight heats the Earth's surface, but the gases block the infrared radiation from exiting back to space. This imbalance causes the Earth to warm, and thus climate change.

Refractive index[link]

The refractive index of air is close to, but just greater than 1. Systematic variations in refractive index can lead to the bending of light rays over long optical paths. One example is that, under some circumstances, observers onboard ships can see other vessels just over the horizon because light is refracted in the same direction as the curvature of the Earth's surface.

The refractive index of air depends on temperature, giving rise to refraction effects when the temperature gradient is large. An example of such effects is the mirage.

Circulation[link]

An idealised view of three large circulation cells.

Atmospheric circulation is the large-scale movement of air through the troposphere, and the means (with ocean circulation) by which heat is distributed around the Earth. The large-scale structure of the atmospheric circulation varies from year to year, but the basic structure remains fairly constant as it is determined by the Earth's rotation rate and the difference in solar radiation between the equator and poles.

Evolution of Earth's atmosphere[link]

Earliest atmosphere[link]

The outgassings of the Earth were stripped away by solar winds early in the history of the planet until a steady state was established, the first atmosphere. Based on today's volcanic evidence, this atmosphere would have contained 60% hydrogen, 20% oxygen (mostly in the form of water vapor), 10% carbon dioxide, 5 to 7% hydrogen sulfide, and smaller amounts of nitrogen, carbon monoxide, free hydrogen, methane and inert gases.^{[citation needed]}

A major rainfall led to the buildup of a vast ocean, enriching the other agents, first carbon dioxide and later nitrogen and inert gases. A major part of carbon dioxide exhalations were soon dissolved in water and built up carbonate sediments.

Second atmosphere[link]

Water-related sediments have been found dating from as early as 3.8 billion years ago.^[17] About 3.4 billion years ago, nitrogen was the major part of the then stable "second atmosphere". An influence of life has to be taken into account rather soon in the history of the atmosphere, since hints of early life forms are to be found as early as 3.5 billion years ago.^[18] The fact that this is not perfectly in line with the 30% lower solar radiance (compared to today) of the early Sun has been described as the "faint young Sun paradox".

The geological record however shows a continually relatively warm surface during the complete early temperature record of the Earth with the exception of one cold glacial phase about 2.4 billion years ago. In the late Archaean eon an oxygen-containing atmosphere began to develop, apparently from photosynthesizing algae which have been found as stromatolite fossils from 2.7 billion years ago. The early basic carbon isotopy (isotope ratio proportions) is very much in line with what is found today,^[19] suggesting that the fundamental features of the carbon cycle were established as early as 4 billion years ago.

Third atmosphere[link]

Oxygen content of the atmosphere over the last billion years. This diagram in more detail

The accretion of continents about 3.5 billion years ago^[20] added plate tectonics, constantly rearranging the continents and also shaping long-term climate evolution by allowing the transfer of carbon dioxide to large land-based carbonate storages. Free oxygen did not exist until about 1.7 billion years ago and this can be seen with the development of the red beds and the end of the banded iron formations. The Earth had a lot of iron in the beginning, and higher amounts of oxygen was not available in the atmosphere until all the iron had ben oxidized. This signifies a shift from a reducing atmosphere to an oxidising atmosphere. O₂ showed major ups and downs until reaching a steady state of more than 15%.^[21] The following time span was the Phanerozoic eon, during which oxygen-breathing metazoan life forms began to appear.

The amount of oxygen in the atmosphere has gone up and down during the last 600 million years. There was a peak 280 million years ago, when the amount of oxygen was about 30 %, much higher than today. The cause of changes in the atmosphere is two main processes: Plants converts carbon dioxide into the bodies of the plants, which emits oxygen into the atmosphere, and break down of pyrite rocks cause sulphur to be added to the oceans. Volcanos cause this sulphur to be oxidized, reducing the amount of oxygen in the atmosphere. But volcanos also emit carbon dioxide, so that plants can convert this to oxygen. The exact cause of the variation of oxygen in the atmosphere is not known. Periods with much oxygen in the atmosphere are believed to cause rapid development of animals. Even if the atmosphere today has only 21 percent oxygen, today is still regarded as a period with rapid development of animals because of a high amount of oxygen in the atmosphere.^[22]

Currently, anthropogenic greenhouse gases are increasing in the atmosphere. According to the Intergovernmental Panel on Climate Change, this increase is the main cause of global warming.^[23]

Air pollution[link]

Air pollution is the introduction of chemicals, particulate matter, or biological materials that cause harm or discomfort to organisms into the atmosphere.^[24] Stratospheric ozone depletion is believed to be caused by air pollution (chiefly from chlorofluorocarbons).^{[citation needed]}

See also[link]

	Atmosphere portal
	Environment portal

References[link]