Air Pollutants: Damaging Our Ozone Layer

Air pollution is a pressing issue that poses significant risks to both human health and the environment. It refers to the release of harmful substances into the Earth's atmosphere, which can have detrimental effects on the planet and its inhabitants. The troposphere, the lowest layer of the Earth's atmosphere, is particularly vulnerable to the impact of air pollutants. This layer contains about three-fourths of all air and is where human-made pollutants, such as nitrogen dioxide and sulfur dioxide, are found. These pollutants can cause respiratory and other diseases and contribute to climate change by trapping heat in the atmosphere.

The troposphere is the lowest layer of the Earth's atmosphere and contains roughly 80% of the mass of the Earth's atmosphere

The troposphere is the lowest layer of the Earth's atmosphere. It extends from the Earth's surface to an average height of about 12 km (7.5 mi; 39,000 ft), though this varies from 9 km (5.6 mi; 30,000 ft) at the poles to 17 km (11 mi; 56,000 ft) at the equator. The troposphere contains roughly 80% of the mass of the Earth's atmosphere, with 50% of this mass found in the lower 5.6 km (3.5 mi; 18,000 ft) of the layer.

The troposphere is denser than the layers above it because more of the atmosphere's weight sits on top of it, causing it to be more severely compressed. It is the only layer accessible by propeller-driven aircraft and is where most conventional aviation activity takes place. The troposphere is also where nearly all atmospheric water vapour or moisture is found, so it is the layer where most of the Earth's weather occurs.

The temperature in the troposphere is warm (around 17º C) near the Earth's surface due to the absorption of infrared radiation by water vapour and other greenhouse gases. The concentration of these gases decreases with altitude, so the heating effect is greatest near the surface. The temperature in the troposphere decreases at a rate of roughly 6.5º C per kilometre of altitude, with the temperature at its upper boundary reaching around -60º C.

Because hot air rises and cold air falls, there is a constant convective overturn of material in the troposphere, giving the layer its name, which means "region of mixing". Weather phenomena such as clouds, rain, dust, and pollutants are all mixed in the troposphere but are eventually washed out by rainfall, making the troposphere self-cleaning.

The troposphere is bounded above by the tropopause, a boundary marked by a temperature inversion (a layer of relatively warm air above a colder one) or an area that is isothermal with height. The tropopause effectively separates the troposphere from the stratosphere, the next major layer of the Earth's atmosphere.

The stratosphere is the second-lowest layer of the Earth's atmosphere and contains the ozone layer

The stratosphere is the second-lowest layer of Earth's atmosphere. It lies above the troposphere and is separated from it by the tropopause. This layer extends from the top of the troposphere at roughly 12 km (7.5 mi; 39,000 ft) above Earth's surface to the stratopause at an altitude of about 50 to 55 km (31 to 34 mi; 164,000 to 180,000 ft). The atmospheric pressure at the top of the stratosphere is roughly 1/1000 the pressure at sea level.

The stratosphere contains the ozone layer, which is the part of Earth's atmosphere that contains relatively high concentrations of that gas. The ozone layer absorbs high-energy ultraviolet (UV) radiation from the Sun, which is harmful to living organisms on the surface of the Earth. The absorption of UV radiation by the ozone layer also causes a temperature inversion, with warmer layers of air located higher (closer to outer space) and cooler layers located lower (closer to the planetary surface of the Earth). This is in contrast to the troposphere, where temperature decreases with altitude.

The stratospheric temperature profile creates very stable atmospheric conditions, so the stratosphere lacks the weather-producing air turbulence prevalent in the troposphere. Consequently, the stratosphere is almost completely free of clouds and other forms of weather. However, polar stratospheric or nacreous clouds are occasionally seen in the lower part of this layer of the atmosphere where the air is coldest. The stratosphere is the highest layer that can be accessed by jet-powered aircraft.

The stratosphere is a region of intense interactions among radiative, dynamical, and chemical processes, with horizontal mixing of gaseous components proceeding much more rapidly than vertical mixing. The overall circulation of the stratosphere is known as Brewer-Dobson circulation, a single-celled circulation spanning from the tropics up to the poles. The stratosphere is also the layer where most meteors burn up upon atmospheric entrance.

The mesosphere is the third highest layer of the Earth's atmosphere and is the coldest place on Earth

The mesosphere is the third highest layer of Earth's atmosphere, located above the stratosphere and below the thermosphere. It extends from the stratopause, at an altitude of about 50 km (31 mi; 160,000 ft) to the mesopause at 80–85 km (50–53 mi; 260,000–280,000 ft) above sea level. The mesosphere is often considered part of the "middle atmosphere", along with the stratosphere, spanning altitudes of approximately 12 to 80 km (7.5 to 49.7 mi) above Earth's surface.

The mesosphere is characterised by decreasing temperatures as altitude increases, reaching as low as −85 °C (−120 °F; 190 K) at the mesopause. This temperature drop is due to the decreasing absorption of solar radiation by the rarefied atmosphere and the diminishing relative ozone concentration as altitude increases. Additionally, the mesosphere experiences increased cooling due to CO2 radiative emission. The mesopause, marking the top of the mesosphere, is the coldest place on Earth, with temperatures below −143 °C (−225 °F; 130 K).

The mesosphere is a transitional area between the familiar terrestrial atmosphere and the region where satellites orbit. It is a poorly understood region that is difficult to access for measurements, as it is too high for airplanes and balloons, and too low for satellites. The mesosphere is mainly accessed by sounding rockets and rocket-powered aircraft.

The mesosphere plays a crucial role in protecting Earth from meteors, as most meteors burn up upon entering this layer. It is also the region where noctilucent clouds, the highest clouds in the atmosphere, are found. These clouds are composed of ice particles formed from the condensation of the scarce water vapour present at this altitude.

The mesosphere exhibits strong zonal (East-West) winds, atmospheric tides, internal atmospheric gravity waves, and planetary waves. These tides and waves originate in the troposphere and lower stratosphere and propagate upwards to the mesosphere. The complex interactions between dynamical phenomena, photochemistry, and heating processes make the mesosphere a highly intriguing and challenging layer of Earth's atmosphere.

The thermosphere is the second-highest layer of the Earth's atmosphere and contains the ionosphere

The thermosphere is the second-highest layer of Earth's atmosphere. It is located between about 80 and 700 kilometres (50 and 440 miles) above the Earth's surface. The thermosphere is known for its high temperatures, which can reach up to 1,500°C or more due to the absorption of intense solar radiation by the remaining oxygen molecules. Despite the high temperatures, the air in this layer is extremely thin and rarefied, with molecules travelling long distances between collisions. This layer is completely cloudless and free of water vapour.

The thermosphere contains the ionosphere in its lower region, up to about 550 kilometres above the Earth's surface. The ionosphere is characterised by the presence of ionised gas particles, formed when high-energy radiation from the Sun knocks electrons loose from their parent atoms and molecules. This process results in the formation of electrically charged atoms and molecules called ions, giving the ionosphere its name. The ionosphere is important for radio communications as it reflects radio waves from the Earth's surface. It is also responsible for the occurrence of auroras, such as the Northern Lights and Southern Lights, which can sometimes be observed in this region.

The thermosphere is influenced by variations in solar activity, which can cause fluctuations in its height and temperature. The top of the thermosphere, known as the thermopause or exobase, can range from 500 to 1,000 kilometres above the Earth's surface. The thermosphere gradually transitions into the exosphere, the outermost layer of the Earth's atmosphere, which extends from the thermopause to about 10,000 kilometres above the Earth's surface.

The thermosphere plays a crucial role in protecting the Earth by absorbing high-energy X-rays and ultraviolet (UV) radiation from the Sun. This absorption process results in a significant increase in temperature within the thermosphere. However, despite the high temperatures, the air in this layer remains extremely cold to human touch due to the low density of molecules. The thermosphere also serves as the orbit for many satellites, including the International Space Station.

The exosphere is the outermost layer of the Earth's atmosphere and is so tenuous that it is sometimes considered part of interplanetary space

The exosphere is the outermost layer of Earth's atmosphere. It extends from the thermopause (or exobase) at the top of the thermosphere to a poorly defined boundary with the solar wind and interplanetary medium. The exosphere is so tenuous that it is sometimes considered part of interplanetary space rather than part of the atmosphere. The altitude of the exobase varies from about 500 kilometres (310 miles) to about 1,000 kilometres (620 miles) in times of higher incoming solar radiation.

The upper limit of the exosphere varies depending on the definition used. Some sources consider it to end at about 10,000 kilometres (6,200 miles), while others place it at about 190,000 kilometres (120,000 miles)—about halfway to the Moon, where the influence of Earth's gravity is similar to the radiation pressure from sunlight. The geocorona, caused by neutral hydrogen, extends to at least 100,000 kilometres (62,000 miles).

The exosphere is composed of extremely low densities of hydrogen, helium, and several heavier molecules, including nitrogen, oxygen, and carbon dioxide closer to the exobase. The atoms and molecules are so far apart that they rarely collide. As a result, the exosphere no longer behaves like a typical gas, and particles constantly escape into space. These free-moving particles follow ballistic trajectories and may migrate in and out of the magnetosphere or the solar wind. The Earth loses about 3 kg of hydrogen, 50 g of helium, and smaller amounts of other constituents every second.

The exosphere is too far above Earth for meteorological phenomena to occur. However, Earth's auroras—the aurora borealis (northern lights) and aurora australis (southern lights)—occur in the lower part of the exosphere, overlapping with the thermosphere. This layer of the atmosphere contains many artificial satellites that orbit the Earth.

While the exosphere is technically part of Earth's atmosphere, it shares many characteristics with outer space. The air in the exosphere is extremely thin and almost akin to the airless void of space. The exosphere gradually fades into the vacuum of space, and there is no clear upper boundary. The average altitude of the International Space Station, for example, is about 330 kilometres (205 miles), placing it in the thermosphere below the exosphere.

Frequently asked questions