Helena Joyce
The Earth's atmosphere is divided into four layers: the troposphere, stratosphere, mesosphere, and thermosphere. The troposphere is the closest layer to the Earth's surface and contains about 75% of the atmosphere's air. It is where weather phenomena occur and is influenced by human-made pollutants, such as nitrogen dioxide, carbon monoxide, and sulfur dioxide, which can negatively impact human health and the environment. The stratosphere lies above the troposphere and contains the ozone layer, which protects life on Earth from harmful ultraviolet radiation. This layer has been partially depleted by ozone-depleting substances (ODS), leading to increased UVB levels and negative consequences for human health, ecosystems, and the climate. While the mesosphere and thermosphere are less affected by pollutants, human activities impact the entire atmosphere, and understanding these interactions is crucial for environmental concerns and space exploration.
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What You'll Learn
- The troposphere contains about 75% of air and almost all water vapour
- The stratosphere contains the ozone layer, which protects us from UV rays
- The mesosphere is where temperature decreases as altitude increases
- The thermosphere is where temperature increases as altitude increases
- Human activities have damaged the ozone layer, leading to increased health risks
The troposphere contains about 75% of air and almost all water vapour
The troposphere is the lowest layer of the Earth's atmosphere. It contains about 75% of the total mass of the planetary atmosphere, with the thickness of the layer varying by a few kilometres according to latitude and season. The troposphere is thicker near the equator and during the summer, and thinner near the poles and in winter. It extends about 8–16 kilometres from the Earth's surface, with an average height of 13 kilometres.
The troposphere is the wettest layer of the atmosphere, containing 99% of the total water vapour in the atmosphere. Water vapour is formed through the processes of evaporation and transpiration from bodies of water and vegetation on the planetary surface. The troposphere is also the layer where most weather phenomena occur, including the formation of clouds and rain.
The temperature of the troposphere decreases at high altitudes, with the lowest temperatures found at the tropopause, the atmospheric boundary between the troposphere and the stratosphere. The temperature decrease is due to the decreasing air pressure and saturation vapour pressure with increasing altitude. The temperature profile of the stratosphere is different from that of the troposphere, with the temperature increasing with altitude.
The troposphere is of particular interest in the study of atmospheric chemistry and air pollution. It is the layer closest to the Earth's surface and contains the largest percentage of the mass of the atmosphere. The rotational friction of the troposphere against the planetary surface affects the flow of air and forms the planetary boundary layer (PBL). The PBL varies in height and is influenced by the turbulence generated by the wind and the heating of the Earth's surface by the sun. This turbulence redistributes heat, moisture, pollutants, and other constituents within the troposphere.
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The stratosphere contains the ozone layer, which protects us from UV rays
The stratosphere is one of the layers of the Earth's atmosphere, situated above the troposphere and below the mesosphere. The stratosphere extends from about 10km to 50km in altitude. Commercial airlines fly in the lower stratosphere. The temperature in the stratosphere increases with altitude, unlike in the troposphere, where it decreases. This warming in the stratosphere is caused by ozone absorbing ultraviolet radiation.
The stratosphere contains the ozone layer, which protects us from harmful UV rays. Ozone is a molecule that contains three oxygen atoms. It is a colourless and highly reactive gas that can be found throughout all layers of the atmosphere. However, most ozone (about 90%) is found in the stratosphere, which begins at about 10–16 kilometres above Earth’s surface, depending on latitude, and extends to an altitude of about 50 kilometres.
The ozone layer absorbs a portion of the radiation from the sun, preventing it from reaching the Earth's surface. Most importantly, it absorbs the portion of UV light called UVBUVBA band ultraviolet radiation with wavelengths from 280-320 nanometers produced by the Sun. UVB is a kind of ultraviolet light from the sun (and sun lamps) that has several harmful effects. It is particularly effective at damaging DNA and is a cause of melanoma and other types of skin cancer. It has also been linked to damage to some materials, crops, and marine organisms.
The ozone layer is crucial for life on Earth because it contains a high concentration of ozone (O₃) molecules. Ozone plays a vital role in absorbing the majority of the sun's harmful UV radiation, specifically the UV-B and UV-C types, which can cause severe damage to living organisms, including skin cancer in humans and various ecological impacts.
Ozone depletion by ozone-depleting substances (ODS) will lead to higher UVB levels, which in turn will cause increased skin cancers and cataracts and potential damage to some marine organisms, plants, and plastics.
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The mesosphere is where temperature decreases as altitude increases
The Earth's atmosphere is divided into four layers: the troposphere, stratosphere, mesosphere, and thermosphere. The troposphere is the closest to the Earth's surface, followed by the stratosphere, mesosphere, and then the thermosphere. The mesosphere is located between 50 and 85 kilometres (31 to 53 miles) above the Earth's surface. It is situated directly above the stratosphere and below the thermosphere.
The mesosphere is an intriguing layer of the Earth's atmosphere, characterised by a unique temperature profile. Unlike the lower layers, where temperature generally increases with altitude, the mesosphere exhibits a decrease in temperature as altitude rises. This phenomenon is a defining feature of the mesosphere, with temperatures dropping to extremely low levels towards the top of this layer.
The temperature decrease in the mesosphere is a result of two primary factors. Firstly, as altitude increases, the absorption of solar radiation by the atmosphere decreases. This is due to the diminishing concentration of ozone, which is the main absorber of UV radiation from the sun. Secondly, the increase in altitude leads to enhanced cooling by carbon dioxide radiative emission, further contributing to the temperature decrease.
The mesosphere is a challenging region to study due to its high altitude. Traditional aircraft and weather balloons cannot reach these extreme heights, and satellites orbit above it, making direct measurements difficult. However, sounding rockets have been used to explore the mesosphere, providing valuable insights into this mysterious layer of the atmosphere.
The mesosphere is not only known for its temperature characteristics but also for its unique phenomena. It is home to noctilucent clouds, which form at incredibly high altitudes near the poles. Additionally, the mesosphere is where most meteors vaporise, leaving behind traces of iron and other metal atoms. The presence of red sprites and blue jets, electrical discharges similar to lightning, further adds to the intrigue of this atmospheric layer.
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The thermosphere is where temperature increases as altitude increases
The Earth's atmosphere is divided into four layers: the troposphere, stratosphere, mesosphere, and thermosphere. The troposphere is the closest layer to the Earth's surface, followed by the stratosphere, the mesosphere, and finally, the thermosphere.
The thermosphere is the second-highest layer of the Earth's atmosphere, extending from the mesopause, which separates it from the mesosphere below it, at an altitude of approximately 50-85 kilometres (31-53 miles or 260,000 feet) to the thermopause at an altitude ranging from 1,600,000 to 3,300,000 feet (487-990 kilometres or 300-600 miles). The thermosphere is considered the upper atmosphere, and it is uninhabited except for the International Space Station and the Tiangong space station, which orbit within this layer.
The thermosphere is unique in that its temperature increases as altitude increases. This is due to the absorption of highly energetic solar radiation, particularly ultraviolet (UV) and X-ray radiation. As altitude increases in the thermosphere, the atmospheric gases become denser, and the absorption of solar radiation by these denser molecules leads to an increase in temperature. This temperature inversion in the thermosphere is in contrast to the stratosphere, where the absorption of radiation by ozone leads to a temperature inversion. The temperature in the thermosphere can rise as high as 1,500°C (2,700°F) or even higher, depending on solar activity. However, due to the low density of molecules in this layer, the temperature may not be perceptible in the usual sense.
The thermosphere is important for space exploration and environmental concerns. It is home to the ionosphere, where ultraviolet radiation from the Sun causes photoionization and photodissociation of molecules, creating electrically charged ions. These ions enable radio waves to be refracted and received beyond the horizon. Additionally, the thermosphere exhibits interesting atmospheric wave behaviour, with internal waves transporting energy upward and external waves playing a more significant role at these altitudes.
While the thermosphere itself does not contain the most pollutants, the troposphere, the lowest layer of the Earth's atmosphere, contains the largest percentage of the mass of the atmosphere and is where most weather phenomena occur. This layer is where human activities have the most impact, with pollutants such as carbon dioxide, carbon monoxide, ozone, and nitrogen oxides affecting the chemical composition of the atmosphere. Ground-level ozone, formed through chemical reactions between oxides of nitrogen and volatile organic compounds, poses significant health risks, especially for vulnerable individuals, and can also harm sensitive ecosystems.
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Human activities have damaged the ozone layer, leading to increased health risks
The ozone layer is a thin shield of gas in the Earth's atmosphere, located in the stratosphere about 9 to 18 miles (15 to 30 km) above the Earth's surface. It absorbs the sun's harmful ultraviolet (UV) rays, specifically the UV-B and UV-C bands, and prevents them from reaching the planet's surface. By absorbing this radiation, the ozone layer helps preserve life on Earth.
However, human activities have damaged this protective layer, primarily through the use and emission of ozone-depleting substances (ODS). ODS include chlorofluorocarbons (CFCs), hydrochlorofluorocarbons (HCFCs), halons, methyl bromide, carbon tetrachloride, hydrobromofluorocarbons, chlorobromomethane, and methyl chloroform. These substances are found in everyday products such as air conditioners, refrigerators, aerosol cans, and industrial solvents. When released into the atmosphere, they break down under intense UV light in the stratosphere, releasing chlorine or bromine atoms that deplete the ozone layer.
The depletion of the ozone layer leads to increased levels of UV-B radiation reaching the Earth's surface. This radiation is harmful to humans, as it increases the risk of skin cancer, cataracts, and a suppressed immune system. It also damages terrestrial plant life, single-cell organisms, and aquatic ecosystems. For example, increased UV-B radiation affects the growth and development of plants, including economically important species such as rice, and reduces the survival rates of phytoplankton, which form the foundation of aquatic food webs.
The effects of ozone depletion on human health have been a significant concern. The Montreal Protocol, adopted in 1987, is an international agreement aimed at protecting the ozone layer by phasing out the production and use of ODSs. It has potentially helped to prevent millions of cases of skin cancer globally and resulted in significant health benefits. Additionally, efforts to reduce ODSs have contributed to slowing down climate change by avoiding the emission of billions of tons of carbon dioxide equivalents.
While there has been progress in reducing the consumption of ODSs globally, the ozone layer remains vulnerable to human activities and natural events. Wildfires, for example, can transport aerosols into the stratosphere, leading to ozone depletion. The increasing frequency and intensity of wildfires driven by global warming pose a growing threat to the ozone layer. Therefore, continued global efforts to reduce ODSs and mitigate climate change are crucial for preserving the health and well-being of all life on Earth.
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Frequently asked questions
The troposphere, the lowest layer of the atmosphere, contains the most pollutants. It contains about 75% of all the air in the atmosphere, and almost all of the water vapour. It is the only layer where weather phenomena occur. Dust and pollutants are injected into the troposphere and become well mixed, but they are eventually washed out by rainfall, making the troposphere self-cleaning.
The main sources of pollutants in the troposphere are human activities, such as burning carbon-containing fuels, which produce carbon dioxide, and automobiles, which produce carbon monoxide.
The stratosphere, the layer above the troposphere, contains the ozone layer, which has been depleted by ozone-depleting substances (ODS) such as chlorofluorocarbons (CFCs). These are organic compounds made up of atoms of carbon, chlorine and fluorine. They deplete the ozone layer when they slowly rise into the stratosphere, are broken down by ultraviolet radiation, release chlorine atoms, and then react with ozone molecules.
