Atmospheric chemistry

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Atmospheric chemistry is a branch of atmospheric science in which the chemistry of the Earth's atmosphere and that of other planets is studied. It is a multidisciplinary approach of research and draws on environmental chemistry, physics, meteorology, computer modeling, oceanography, geology and volcanology and other disciplines. Research is increasingly connected with other areas of study such as climatology.

Chemistry is the scientific discipline involved with elements and compounds composed of atoms, molecules and ions: their composition, structure, properties, behavior and the changes they undergo during a reaction with other substances.

Atmosphere of Earth Layer of gases surrounding the planet Earth

The atmosphere of Earth is the layer of gases, commonly known as air, that surrounds the planet Earth and is retained by Earth's gravity. The atmosphere of Earth protects life on Earth by creating pressure allowing for liquid water to exist on the Earth's surface, absorbing ultraviolet solar radiation, warming the surface through heat retention, and reducing temperature extremes between day and night.

Environmental chemistry The scientific study of the chemical and phenomena that occur in natural places

Environmental chemistry is the scientific study of the chemical and biochemical phenomena that occur in natural places. It should not be confused with green chemistry, which seeks to reduce potential pollution at its source. It can be defined as the study of the sources, reactions, transport, effects, and fates of chemical species in the air, soil, and water environments; and the effect of human activity and biological activity on these. Environmental chemistry is an interdisciplinary science that includes atmospheric, aquatic and soil chemistry, as well as heavily relying on analytical chemistry and being related to environmental and other areas of science.

The composition and chemistry of the Earth's atmosphere is of importance for several reasons, but primarily because of the interactions between the atmosphere and living organisms. The composition of the Earth's atmosphere changes as result of natural processes such as volcano emissions, lightning and bombardment by solar particles from corona. It has also been changed by human activity and some of these changes are harmful to human health, crops and ecosystems. Examples of problems which have been addressed by atmospheric chemistry include acid rain, ozone depletion, photochemical smog, greenhouse gases and global warming. Atmospheric chemists seek to understand the causes of these problems, and by obtaining a theoretical understanding of them, allow possible solutions to be tested and the effects of changes in government policy evaluated.

Volcano A rupture in the crust of a planetary-mass object that allows hot lava, volcanic ash, and gases to escape from a magma chamber below the surface

A volcano is a rupture in the crust of a planetary-mass object, such as Earth, that allows hot lava, volcanic ash, and gases to escape from a magma chamber below the surface.

Lightning atmospheric discharge of electricity

Lightning is a violent and sudden electrostatic discharge where two electrically charged regions in the atmosphere temporarily equalize themselves, usually during a thunderstorm.

Corona Aura of plasma that surrounds the Sun and other stars

A corona is an aura of plasma that surrounds the Sun and other stars. The Sun's corona extends millions of kilometres into outer space and is most easily seen during a total solar eclipse, but it is also observable with a coronagraph. The word corona is a Latin word meaning "crown", from the Ancient Greek κορώνη.

Atmospheric composition

Visualisation of composition by volume of Earth's atmosphere. Water vapour is not included as it is highly variable. Each tiny cube (such as the one representing krypton) has one millionth of the volume of the entire block. Data is from NASA Langley. Atmospheric composition Langley.svg
Visualisation of composition by volume of Earth's atmosphere. Water vapour is not included as it is highly variable. Each tiny cube (such as the one representing krypton) has one millionth of the volume of the entire block. Data is from NASA Langley.
Average composition of dry atmosphere (mole fractions)
Gasper NASA
Nitrogen, N278.084%
Oxygen, O2 [1] 20.946%
Minor constituents (mole fractions in ppm)
Argon, Ar9340
Carbon dioxide, CO2400
Neon, Ne18.18
Helium, He5.24
Methane, CH41.7
Krypton, Kr1.14
Hydrogen, H20.55
Nitrous oxide, N2O0.5
Xenon, Xe0.09
Nitrogen dioxide, NO20.02
Water
Water vapour Highly variable;
typically makes up about 1%

Notes: the concentration of CO2 and CH4 vary by season and location. The mean molecular mass of air is 28.97 g/mol. Ozone (O3) is not included due to its high variability.

In chemistry, concentration is the abundance of a constituent divided by the total volume of a mixture. Several types of mathematical description can be distinguished: mass concentration, molar concentration, number concentration, and volume concentration. A concentration can be any kind of chemical mixture, but most frequently solutes and solvents in solutions. The molar (amount) concentration has variants such as normal concentration and osmotic concentration.

Ozone chemical compound

Ozone, or trioxygen, is an inorganic molecule with the chemical formula 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 O
2
(dioxygen). Ozone is formed from dioxygen by the action of ultraviolet light (UV) and electrical discharges within the Earth's atmosphere. It is present in very low concentrations throughout the latter, with its highest concentration high in the ozone layer of the stratosphere, which absorbs most of the Sun's ultraviolet (UV) radiation.

History

Schematic of chemical and transport processes related to atmospheric composition. Atmosphere composition diagram-en.svg
Schematic of chemical and transport processes related to atmospheric composition.

The ancient Greeks regarded air as one of the four elements. The first scientific studies of atmospheric composition began in the 18th century, as chemists such as Joseph Priestley, Antoine Lavoisier and Henry Cavendish made the first measurements of the composition of the atmosphere.

The Greeks or Hellenes are an ethnic group native to Greece, Cyprus, southern Albania, Italy, Turkey, Egypt and, to a lesser extent, other countries surrounding the Mediterranean Sea. They also form a significant diaspora, with Greek communities established around the world.

Joseph Priestley English theologian, chemist, educator, and political theorist

Joseph Priestley was an 18th-century English Separatist theologian, natural philosopher, chemist, innovative grammarian, multi-subject educator, and liberal political theorist who published over 150 works. He has historically been credited with the discovery of oxygen, having isolated it in its gaseous state, although Carl Wilhelm Scheele and Antoine Lavoisier also have strong claims to the discovery.

Antoine Lavoisier French chemist

Antoine-Laurent de Lavoisier was a French nobleman and chemist who was central to the 18th-century chemical revolution and who had a large influence on both the history of chemistry and the history of biology. He is widely considered in popular literature as the "father of modern chemistry".

In the late 19th and early 20th centuries interest shifted towards trace constituents with very small concentrations. One particularly important discovery for atmospheric chemistry was the discovery of ozone by Christian Friedrich Schönbein in 1840.

Christian Friedrich Schönbein German-Swiss chemist, discoverer of guncotton and ozone

Prof Christian Friedrich Schönbein HFRSE(18 October 1799 – 29 August 1868) was a German-Swiss chemist who is best known for inventing the fuel cell (1838) at the same time as William Robert Grove and his discoveries of guncotton and ozone.

In the 20th century atmospheric science moved on from studying the composition of air to a consideration of how the concentrations of trace gases in the atmosphere have changed over time and the chemical processes which create and destroy compounds in the air. Two particularly important examples of this were the explanation by Sydney Chapman and Gordon Dobson of how the ozone layer is created and maintained, and the explanation of photochemical smog by Arie Jan Haagen-Smit. Further studies on ozone issues led to the 1995 Nobel Prize in Chemistry award shared between Paul Crutzen, Mario Molina and Frank Sherwood Rowland. [2]

Ozone layer The region of Earths stratosphere that absorbs most of the Suns UV radiation

The ozone layer or ozone shield is a region of Earth's stratosphere that absorbs most of the Sun's ultraviolet radiation. It contains high concentration of ozone (O3) in relation to other parts of the atmosphere, although still small in relation to other gases in the stratosphere. The ozone layer contains less than 10 parts per million of ozone, while the average ozone concentration in Earth's atmosphere as a whole is about 0.3 parts per million. The ozone layer is mainly found in the lower portion of the stratosphere, from approximately 15 to 35 kilometers (9.3 to 21.7 mi) above Earth, although its thickness varies seasonally and geographically.

Arie Jan Haagen-Smit was a Dutch chemist. He is best known for linking the smog in Southern California to automobiles and is therefore known by many as the "father" of air pollution control. After serving as an original board member of the Motor Vehicle Pollution Control Board, formed in 1960 to combat the smog, Dr. Haagen-Smit became the California Air Resources Board's first chairman in 1968. Shortly before his death, of lung cancer, the Air Resources Board's El Monte Laboratory was named after him.

In the 21st century the focus is now shifting again. Atmospheric chemistry is increasingly studied as one part of the Earth system. Instead of concentrating on atmospheric chemistry in isolation the focus is now on seeing it as one part of a single system with the rest of the atmosphere, biosphere and geosphere. An especially important driver for this is the links between chemistry and climate such as the effects of changing climate on the recovery of the ozone hole and vice versa but also interaction of the composition of the atmosphere with the oceans and terrestrial ecosystems.

M15-162b-EarthAtmosphere-CarbonDioxide-FutureRoleInGlobalWarming-Simulation-20151109.jpg
Carbon dioxide in Earth's atmosphere if half of global-warming emissions [3] [4] are not absorbed.
(NASA simulation; 9 November 2015)
15-233-Earth-GlobalAirQuality-2014NitrogenDioxideLevels-20151214.jpg
Nitrogen dioxide 2014 - global air quality levels
(released 14 December 2015). [5]

Methodology

Observations, lab measurements, and modeling are the three central elements in atmospheric chemistry. Progress in atmospheric chemistry is often driven by the interactions between these components and they form an integrated whole. For example, observations may tell us that more of a chemical compound exists than previously thought possible. This will stimulate new modelling and laboratory studies which will increase our scientific understanding to a point where the observations can be explained.

Observation

Observations of atmospheric chemistry are essential to our understanding. Routine observations of chemical composition tell us about changes in atmospheric composition over time. One important example of this is the Keeling Curve - a series of measurements from 1958 to today which show a steady rise in of the concentration of carbon dioxide (see also ongoing measurements of atmospheric CO2). Observations of atmospheric chemistry are made in observatories such as that on Mauna Loa and on mobile platforms such as aircraft (e.g. the UK's Facility for Airborne Atmospheric Measurements), ships and balloons. Observations of atmospheric composition are increasingly made by satellites with important instruments such as GOME and MOPITT giving a global picture of air pollution and chemistry. Surface observations have the advantage that they provide long term records at high time resolution but are limited in the vertical and horizontal space they provide observations from. Some surface based instruments e.g. LIDAR can provide concentration profiles of chemical compounds and aerosol but are still restricted in the horizontal region they can cover. Many observations are available on line in Atmospheric Chemistry Observational Databases.

Laboratory studies

Measurements made in the laboratory are essential to our understanding of the sources and sinks of pollutants and naturally occurring compounds. These experiments are performed in controlled environments that allow for the individual evaluation of specific chemical reactions or the assessment of properties of a particular atmospheric constituent. [6] Types of analysis that are of interest includes both those on gas-phase reactions, as well as heterogeneous reactions that are relevant to the formation and growth of aerosols. Also of high importance is the study of atmospheric photochemistry which quantifies how the rate in which molecules are split apart by sunlight and what resulting products are. In addition, thermodynamic data such as Henry's law coefficients can also be obtained.

Modeling

In order to synthesise and test theoretical understanding of atmospheric chemistry, computer models (such as chemical transport models) are used. Numerical models solve the differential equations governing the concentrations of chemicals in the atmosphere. They can be very simple or very complicated. One common trade off in numerical models is between the number of chemical compounds and chemical reactions modelled versus the representation of transport and mixing in the atmosphere. For example, a box model might include hundreds or even thousands of chemical reactions but will only have a very crude representation of mixing in the atmosphere. In contrast, 3D models represent many of the physical processes of the atmosphere but due to constraints on computer resources will have far fewer chemical reactions and compounds. Models can be used to interpret observations, test understanding of chemical reactions and predict future concentrations of chemical compounds in the atmosphere. One important current trend is for atmospheric chemistry modules to become one part of earth system models in which the links between climate, atmospheric composition and the biosphere can be studied.

Some models are constructed by automatic code generators (e.g. Autochem or KPP). In this approach a set of constituents are chosen and the automatic code generator will then select the reactions involving those constituents from a set of reaction databases. Once the reactions have been chosen the ordinary differential equations (ODE) that describe their time evolution can be automatically constructed.

See also

Related Research Articles

Ozone depletion Stratospheric phenomena of Earth

Ozone depletion describes two related events observed since the late 1970s: a steady lowering of about four percent in the total amount of ozone in Earth's atmosphere, and a much larger springtime decrease in stratospheric ozone around Earth's polar regions. The latter phenomenon is referred to as the ozone hole. There are also springtime polar tropospheric ozone depletion events in addition to these stratospheric events.

Atmospheric sciences The study of the atmosphere, its processes, and interactions with other systems

Atmospheric sciences are the study of the Earth's atmosphere, its processes, the effects other systems have on the atmosphere, and the effects of the atmosphere on these other systems. Meteorology includes atmospheric chemistry and atmospheric physics with a major focus on weather forecasting. Climatology is the study of atmospheric changes that define average climates and their change over time, due to both natural and anthropogenic climate variability. Aeronomy is the study of the upper layers of the atmosphere, where dissociation and ionization are important. Atmospheric science has been extended to the field of planetary science and the study of the atmospheres of the planets of the solar system.

Tropospheric ozone constituent gas of the troposphere

Ozone (O3) is a trace gas of the troposphere, with an average concentration of 20-30 parts per billion by volume (ppbv), with close to 100 ppbv in polluted areas. Ozone is also an important constituent of the stratosphere, where the ozone layer exists. The troposphere is the lowest layer of the Earth's atmosphere. It extends from the ground up to a variable height of approximately 14 kilometers above sea level. Ozone is least concentrated in the ground layer (or planetary boundary layer) of the troposphere. It's concentration increases as height above sea level increases, with a maximum concentration at the tropopause. About 90% of total ozone in the atmosphere is in the stratosphere, and 10% is in the troposphere. Although tropospheric ozone is less concentrated than stratospheric ozone, it is of concern because of its health effects. Ozone in the troposphere is considered a greenhouse gas, and may contribute to global warming.

Hydroxyl radical radical composed by one atom of oxygen and one atom of hydrogen

The hydroxyl radical, OH, is the neutral form of the hydroxide ion (OH). Hydroxyl radicals are highly reactive (easily becoming hydroxyl groups) and consequently short-lived; however, they form an important part of radical chemistry. Most notably hydroxyl radicals are produced from the decomposition of hydroperoxides (ROOH) or, in atmospheric chemistry, by the reaction of excited atomic oxygen with water. It is also an important radical formed in radiation chemistry, since it leads to the formation of hydrogen peroxide and oxygen, which can enhance corrosion and SCC in coolant systems subjected to radioactive environments. Hydroxyl radicals are also produced during UV-light dissociation of H2O2 (suggested in 1879) and likely in Fenton chemistry, where trace amounts of reduced transition metals catalyze peroxide-mediated oxidations of organic compounds.

Paul J. Crutzen Dutch climatologist

Paul Jozef Crutzen is a Dutch, Nobel Prize-winning, atmospheric chemist. He is known for work on climate change research and for popularizing the term Anthropocene to describe a proposed new era when human actions have a drastic effect on the Earth.

Cooperative Institute for Research in Environmental Sciences

The Cooperative Institute for Research in Environmental Sciences (CIRES) is a research institute that is sponsored jointly by the National Oceanic and Atmospheric Administration (NOAA) Office of Oceanic and Atmospheric Research (OAR) and the University of Colorado Boulder (CU). CIRES scientists study the Earth system, including the atmosphere, hydrosphere, cryosphere, biosphere, and geosphere, and communicate these findings to decision makers, the scientific community, and the public.

In atmospheric chemistry, NOx is a generic term for the nitrogen oxides that are most relevant for air pollution, namely nitric oxide (NO) and nitrogen dioxide (NO2). These gases contribute to the formation of smog and acid rain, as well as affecting tropospheric ozone.

Max Planck Institute for Chemistry

The Max Planck Institute for Chemistry is a non-university research institute under the auspices of the Max Planck Society. It is based in Mainz.

Atmospheric chemistry observational databases

Over the last two centuries many environmental chemical observations have been made from a variety of ground-based, airborne, and orbital platforms and deposited in databases. Many of these databases are publicly available. All of the instruments mentioned in this article give online public access to their data. These observations are critical in developing our understanding of the Earth's atmosphere and issues such as climate change, ozone depletion and air quality. Some of the external links provide repositories of many of these datasets in one place. For example, the Cambridge Atmospheric Chemical Database, is a large database in a uniform ASCII format. Each observation is augmented with the meteorological conditions such as the temperature, potential temperature, geopotential height, and equivalent PV latitude.

Stratospheric sulfur aerosols sulfur-rich particles in the stratosphere

Stratospheric sulfur aerosols are sulfur-rich particles which exist in the stratosphere region of the Earth's atmosphere. The layer of the atmosphere in which they exist is known as the Junge layer, or simply the stratospheric aerosol layer. These particles consist of a mixture of sulfuric acid and water. They are created naturally, such as by photochemical decomposition of sulfur-containing gases, e.g. carbonyl sulfide. When present in high levels, e.g. after a strong volcanic eruption such as Mount Pinatubo, they produce a cooling effect, by reflecting sunlight, and by modifying clouds as they fall out of the stratosphere. This cooling may persist for a few years before the particles fall out.

Greenhouse gas gas in an atmosphere that absorbs and emits radiation within the thermal infrared range

A greenhouse gas is a gas that absorbs and emits radiant energy within the thermal infrared range. Greenhouse gases cause the greenhouse effect. The primary greenhouse gases in Earth's atmosphere are water vapor, carbon dioxide, methane, nitrous oxide and ozone. Without greenhouse gases, the average temperature of Earth's surface would be about −18 °C (0 °F), rather than the present average of 15 °C (59 °F). The atmospheres of Venus, Mars and Titan also contain greenhouse gases.

Atmospheric methane

Atmospheric methane is the methane present in Earth's atmosphere. Atmospheric methane concentrations are of interest because it is one of the most potent greenhouse gases in Earth's atmosphere. Atmospheric methane is rising. The 100-year global warming potential of methane is 28. That is, over a 100-year period, it traps 28 times more heat per mass unit than carbon dioxide and 32 times the effect when accounting for aerosol interactions. Global methane concentrations had risen from 722 parts per billion (ppb) in pre-industrial times to 1800 ppb by 2011, an increase by a factor of 2.5 and the highest value in at least 800,000 years. Its concentration is higher in the Northern Hemisphere since most sources are located on land and the Northern Hemisphere has more land mass. The concentrations vary seasonally, with, for example, a minimum in the northern tropics during April−May mainly due to removal by the hydroxyl radical.

Greenhouse gas monitoring

Greenhouse gas monitoring is the direct measurement of greenhouse gas emissions and levels. There are several different methods of measuring carbon dioxide concentrations in the atmosphere, including infrared analyzing and manometry. Methane and nitrous oxide are measured by other instruments. Greenhouse gases are measured by satellite monitoring such as the Orbiting Carbon Observatory and networks of ground stations such as the Integrated Carbon Observation System.

SAGE III on ISS

SAGE III on ISS is the fourth generation of a series of NASA Earth-observing instruments, known as the Stratospheric Aerosol and Gas Experiment. The first SAGE III instrument was launched on the Russian Meteor (satellite) spacecraft. The recently revised SAGE III will be mounted to the International Space Station where it will use the unique vantage point of ISS to make long-term measurements of ozone, aerosols, water vapor, and other gases in Earth's atmosphere.

Barbara J. Finlayson-Pitts is an American atmospheric chemist. She is a professor in the chemistry department at the University of California, Irvine and is the Director of AirUCI Institute. Finlayson-Pitts and James N. Pitts, Jr. are the authors of Chemistry of the Upper and Lower Atmosphere: Theory, Experiments, and Applications (1999). She has been a member of the National Academy of Sciences since 2006 and is the laureate for the 2017 Garvan–Olin Medal.

Dr. Neil Trivett Global Atmosphere Watch Observatory

The Dr. Neil Trivett Global Atmosphere Watch Observatory is an atmospheric baseline station operated by Environment and Climate Change Canada located at Alert, Nunavut, on the north-eastern tip of Ellesmere Island, about 800 km south of the geographic north pole.

Flash-gas (petroleum)

In an oil and gas production, flash-gas is a spontaneous vapor that is produced from the heating or depressurization of the extracted oil mixture during different phases of production. Flashing, or flash evaporation, is the term that describes this process of volatile components suddenly vaporizing from their liquid state. This often happens during the transportation of petroleum products through pipelines and into vessels, such as when the stream from a common separation unit flows into an on-site atmospheric storage tank. Vessels that are used to intentionally “flash” a mixture of gas and saturated liquids are aptly named "flash drums." A type of vapor-liquid separator. A venting apparatus is used in these vessels to prevent damage due to increasing pressure, extreme cases of this are referred to as boiling liquid expanding vapor explosion (BLEVE).

References

  1. Zimmer, Carl (3 October 2013). "Earth's Oxygen: A Mystery Easy to Take for Granted". The New York Times . Retrieved 3 October 2013.
  2. "Press Release - 1995 Nobel Prize in Chemistry". The Nobel Prize. Nobel Prize Org. October 11, 1995.
  3. St. Fleur, Nicholas (10 November 2015). "Atmospheric Greenhouse Gas Levels Hit Record, Report Says". The New York Times. Retrieved 11 November 2015.
  4. Ritter, Karl (9 November 2015). "UK: In 1st, global temps average could be 1 degree C higher". AP News . Retrieved 11 November 2015.
  5. Cole, Steve; Gray, Ellen (14 December 2015). "New NASA Satellite Maps Show Human Fingerprint on Global Air Quality". NASA . Retrieved 14 December 2015.
  6. National Academies of Sciences, Engineering, and Medicine (2016). Future of Atmospheric Research: Remembering Yesterday, Understanding Today, Anticipating Tomorrow. Washington, DC: The National Academies Press. p. 15. ISBN   978-0-309-44565-8.

Further reading