Atmospheric chemistry is a branch of

atmospheric science Atmospheric science is the study of the Atmosphere of Earth, Earth's atmosphere and its various inner-working physical processes. Meteorology includes atmospheric chemistry and atmospheric physics with a major focus on weather forecasting. Clima ...

that studies the

chemistry Chemistry is the scientific study of the properties and behavior of matter. It is a physical science within the natural sciences that studies the chemical elements that make up matter and chemical compound, compounds made of atoms, molecules a ...

of the

Earth's atmosphere The atmosphere of Earth is composed of a layer of gas mixture that surrounds the Earth's planetary surface (both lands and oceans), known collectively as air, with variable quantities of suspended aerosols and particulates (which create weathe ...

and that of other planets. This

multidisciplinary approach An academic discipline or academic field is a subdivision of knowledge that is taught and researched at the college or university level. Disciplines are defined (in part) and recognized by the academic journals in which research is published, a ...

of research draws on

environmental chemistry 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 ...

physics Physics is the scientific study of matter, its Elementary particle, fundamental constituents, its motion and behavior through space and time, and the related entities of energy and force. "Physical science is that department of knowledge whi ...

meteorology Meteorology is the scientific study of the Earth's atmosphere and short-term atmospheric phenomena (i.e. weather), with a focus on weather forecasting. It has applications in the military, aviation, energy production, transport, agricultur ...

computer modeling Computer simulation is the running of a mathematical model on a computer, the model being designed to represent the behaviour of, or the outcome of, a real-world or physical system. The reliability of some mathematical models can be determin ...

oceanography Oceanography (), also known as oceanology, sea science, ocean science, and marine science, is the scientific study of the ocean, including its physics, chemistry, biology, and geology. It is an Earth science, which covers a wide range of to ...

geology Geology (). is a branch of natural science concerned with the Earth and other astronomical objects, the rocks of which they are composed, and the processes by which they change over time. Modern geology significantly overlaps all other Earth ...

and

volcanology Volcanology (also spelled vulcanology) is the study of volcanoes, lava, magma and related geology, geological, geophysical and geochemistry, geochemical phenomena (volcanism). The term ''volcanology'' is derived from the Latin language, Latin ...

climatology Climatology (from Greek , ''klima'', "slope"; and , '' -logia'') or climate science is the scientific study of Earth's climate, typically defined as weather conditions averaged over a period of at least 30 years. Climate concerns the atmospher ...

and other disciplines to understand both natural and human-induced changes in atmospheric composition. Key areas of research include the behavior of trace gasses, the formation of pollutants, and the role of aerosols and greenhouse gasses. Through a combination of observations, laboratory experiments, and computer modeling, atmospheric chemists investigate the causes and consequences of atmospheric changes.

Atmospheric composition

The composition and chemistry of the Earth's atmosphere is important for several reasons, but primarily because of the interactions between the atmosphere and

living organisms An organism is any living thing that functions as an individual. Such a definition raises more problems than it solves, not least because the concept of an individual is also difficult. Many criteria, few of them widely accepted, have been pro ...

. Natural processes such as

volcano A volcano is commonly defined as a vent or fissure 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. On Earth, volcanoes are most oft ...

emissions,

lightning Lightning is a natural phenomenon consisting of electrostatic discharges occurring through the atmosphere between two electrically charged regions. One or both regions are within the atmosphere, with the second region sometimes occurring on ...

and bombardment by solar particles from

corona Corona (from the Latin for 'crown') most commonly refers to: * Stellar corona, the outer atmosphere of the Sun or another star * Corona (beer), a Mexican beer * Corona, informal term for the coronavirus or disease responsible for the COVID-19 ...

changes the composition of the Earth's atmosphere. It has also been changed by human activity and some of these changes are harmful to human health, crops and ecosystems.

Trace gas composition

Besides the major components listed above, the Earth's atmosphere contains many trace gas species that vary significantly depending on nearby sources and sinks. These trace gasses include compounds such as CFCs/HCFCs which are particularly damaging to the ozone layer, and H2S which has a characteristic foul odor of rotten eggs and can be smelt in concentrations as low as 0.47 ppb. Some ''approximate'' amounts near the surface of some additional gasses are listed below. In addition to gasses, the atmosphere contains particles such as

aerosol An aerosol is a suspension (chemistry), suspension of fine solid particles or liquid Drop (liquid), droplets in air or another gas. Aerosols can be generated from natural or Human impact on the environment, human causes. The term ''aerosol'' co ...

, which includes examples such as droplets, ice crystals, bacteria, and dust.

History

The first scientific studies of atmospheric composition began in the 18th century when chemists such as

Joseph Priestley Joseph Priestley (; 24 March 1733 – 6 February 1804) was an English chemist, Unitarian, Natural philosophy, natural philosopher, English Separatist, separatist theologian, Linguist, grammarian, multi-subject educator and Classical libera ...

Antoine Lavoisier Antoine-Laurent de Lavoisier ( ; ; 26 August 17438 May 1794), When reduced without charcoal, it gave off an air which supported respiration and combustion in an enhanced way. He concluded that this was just a pure form of common air and that i ...

and

Henry Cavendish Henry Cavendish ( ; 10 October 1731 – 24 February 1810) was an English experimental and theoretical chemist and physicist. He is noted for his discovery of hydrogen, which he termed "inflammable air". He described the density of inflammable a ...

made the first measurements of the composition of the atmosphere. In the late 19th and early 20th centuries, researchers shifted their interest towards trace constituents with very low concentrations. An important finding from this era was the discovery of

ozone Ozone () (or trioxygen) is an Inorganic compound, inorganic molecule with the chemical formula . 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 , break ...

Christian Friedrich Schönbein 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. He a ...

in 1840. In the 20th century atmospheric science moved from studying the composition of air to consider how the concentrations of trace gasses in the atmosphere have changed over time and the chemical processes which create and destroy compounds in the air. Two important outcomes were the explanation by Sydney Chapman and Gordon Dobson of how the

ozone layer The ozone layer or ozone shield is a region of Earth's stratosphere that absorption (electromagnetic radiation), absorbs most of the Sun's ultraviolet radiation. It contains a high concentration of ozone (O3) in relation to other parts of the a ...

is created and maintained, and

Arie Jan Haagen-Smit Arie Jan Haagen-Smit (December 22, 1900 – March 17, 1977) 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 ...

’s explanation of

photochemical smog Smog, or smoke fog, is a type of intense air pollution. The word "smog" was coined in the early 20th century, and is a portmanteau of the words ''smoke'' and '' fog'' to refer to smoky fog due to its opacity, and odour. The word was then int ...

. Further studies on ozone issues led to the 1995 Nobel Prize in Chemistry award shared between

Paul Crutzen Paul Jozef Crutzen (; 3 December 1933 – 28 January 2021) was a Dutch meteorologist and atmospheric chemistry, atmospheric chemist. In 1995, he was awarded the Nobel Prize in Chemistry alongside Mario Molina and F. Sherwood Rowland, Frank Sherw ...

Mario Molina Mario José Molina-Pasquel Henríquez (19 March 19437 October 2020) was a Mexican physical chemist. He played a pivotal role in the discovery of the Antarctic ozone hole, and was a co-recipient of the 1995 Nobel Prize in Chemistry for his role ...

and

Frank Sherwood Rowland Frank Sherwood "Sherry" Rowland (June 28, 1927 – March 10, 2012) was an American Nobel laureate and a professor of chemistry at the University of California, Irvine. His research was on atmospheric chemistry and chemical kinetics. His b ...

. In the 21st century the focus is now shifting again. Instead of concentrating on atmospheric chemistry in isolation, it is now seen as one part of the

Earth system Earth system science (ESS) is the application of systems science to the Earth. In particular, it considers interactions and 'feedbacks', through material and energy fluxes, between the Earth's sub-systems' cycles, processes and "spheres"—atmosp ...

with the rest of the

atmosphere An atmosphere () is a layer of gases that envelop an astronomical object, held in place by the gravity of the object. A planet retains an atmosphere when the gravity is great and the temperature of the atmosphere is low. A stellar atmosph ...

biosphere The biosphere (), also called the ecosphere (), is the worldwide sum of all ecosystems. It can also be termed the zone of life on the Earth. The biosphere (which is technically a spherical shell) is virtually a closed system with regard to mat ...

and

geosphere There are several conflicting usages of geosphere, variously defined. In Aristotelian physics, the term was applied to four spherical ''natural places'', concentrically nested around the center of the Earth, as described in the lectures '' Ph ...

. A driving force for this link is the relationship between chemistry and

climate Climate is the long-term weather pattern in a region, typically averaged over 30 years. More rigorously, it is the mean and variability of meteorological variables over a time spanning from months to millions of years. Some of the meteoro ...

. The changing climate and the recovery of the ozone hole and the interaction of the composition of the atmosphere with the oceans and terrestrial

ecosystems An ecosystem (or ecological system) is a system formed by Organism, organisms in interaction with their Biophysical environment, environment. The Biotic material, biotic and abiotic components are linked together through nutrient cycles and en ...

are examples of the interdependent relationships between Earth's systems. A new field of extraterrestrial atmospheric chemistry has also recently emerged. Astrochemists analyze the atmospheric compositions of the

Solar System The Solar SystemCapitalization of the name varies. The International Astronomical Union, the authoritative body regarding astronomical nomenclature, specifies capitalizing the names of all individual astronomical objects but uses mixed "Sola ...

and

exoplanets An exoplanet or extrasolar planet is a planet outside the Solar System. The first confirmed detection of an exoplanet was in 1992 around a pulsar, and the first detection around a main-sequence star was in 1995. A different planet, first detec ...

to determine the formation of astronomical objects and find habitual conditions for Earth-like life.

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 modeling and laboratory studies which will increase our scientific understanding to a level where we can explain the observations.

Observation

Field observations of chemical systems are essential to understanding atmospheric processes and determining the accuracy of models. Atmospheric chemistry measurements are long term to observe continuous trends or short term to observe smaller variations. In situ and remote measurements can be made using observatories, satellites, field stations, and laboratories. Routine observations of chemical composition show changes in atmospheric composition over time. Observatories such as the

Mauna Loa Mauna Loa (, ; ) is one of five volcanoes that form the Island of Hawaii in the U.S. state of Hawaii in the Pacific Ocean. Mauna Loa is Earth's largest active volcano by both mass and volume. It was historically considered to be the largest ...

and mobile platforms such as aircraft ships and balloons (e.g. the UK's

Facility for Airborne Atmospheric Measurements The FAAM Airborne Laboratory is an atmospheric science research facility. It is based on the Cranfield University campus alongside Cranfield Airport in Bedfordshire, England. It was formed by a collaboration between the Met Office and the Nat ...

) study chemical compositions and weather dynamics. An application of long term observations is the Keeling Curve - a series of measurements from 1958 to today which show a steady rise in the concentration of

carbon dioxide Carbon dioxide is a chemical compound with the chemical formula . It is made up of molecules that each have one carbon atom covalent bond, covalently double bonded to two oxygen atoms. It is found in a gas state at room temperature and at norma ...

(see also ongoing measurements of atmospheric CO₂). Observations of atmospheric composition are increasingly made by

satellites A satellite or an artificial satellite is an object, typically a spacecraft, placed into orbit around a celestial body. They have a variety of uses, including communication relay, weather forecasting, navigation ( GPS), broadcasting, scientif ...

by passive and active

remote sensing Remote sensing is the acquisition of information about an physical object, object or phenomenon without making physical contact with the object, in contrast to in situ or on-site observation. The term is applied especially to acquiring inform ...

with important instruments such as GOME and

MOPITT MOPITT (Measurements of Pollution in the Troposphere) is an ongoing astronomical instrument aboard NASA's Terra satellite that measures global tropospheric carbon monoxide levels. It is part of NASA's Earth Observing System (EOS), and combined ...

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 Lidar (, also LIDAR, an acronym of "light detection and ranging" or "laser imaging, detection, and ranging") is a method for determining ranging, ranges by targeting an object or a surface with a laser and measuring the time for the reflected li ...

can provide concentration profiles of chemical compounds and aerosols but are still restricted in the horizontal region they can cover. Many observations are available online in Atmospheric Chemistry Observational Databases

Laboratory studies

Laboratory studies help understand the complex interactions from Earth’s systems that can be difficult to measure on a large scale. Experiments are performed in controlled environments, such as aerosol chambers, that allow for the individual evaluation of specific chemical reactions or the assessment of properties of a particular atmospheric constituent. A closely related subdiscipline is atmospheric

photochemistry Photochemistry is the branch of chemistry concerned with the chemical effects of light. Generally, this term is used to describe a chemical reaction caused by absorption of ultraviolet (wavelength from 100 to 400 Nanometre, nm), visible ligh ...

, which quantifies the rate that molecules are split apart by sunlight, determines the resulting products, and obtains

thermodynamic Thermodynamics is a branch of physics that deals with heat, work, and temperature, and their relation to energy, entropy, and the physical properties of matter and radiation. The behavior of these quantities is governed by the four laws of th ...

data such as

Henry's law In physical chemistry, Henry's law is a gas law that states that the amount of dissolved gas in a liquid is directly proportional at equilibrium to its partial pressure above the liquid. The proportionality factor is called Henry's law constant ...

coefficients. Laboratory measurements are essential to understanding the sources and sinks of pollutants and naturally occurring compounds. Types of analysis that are of interest include both those on gas-phase reactions, as well as

heterogeneous Homogeneity and heterogeneity are concepts relating to the uniformity of a substance, process or image. A homogeneous feature is uniform in composition or character (i.e., color, shape, size, weight, height, distribution, texture, language, i ...

reactions that are relevant to the formation and growth of

aerosols An aerosol is a suspension of fine solid particles or liquid droplets in air or another gas. Aerosols can be generated from natural or human causes. The term ''aerosol'' commonly refers to the mixture of particulates in air, and not to t ...

. Commonly used instruments to measure aerosols include ambient and particulate air samplers, scanning mobility particle sizers, and

mass spectrometers Mass spectrometry (MS) is an analytical technique that is used to measure the mass-to-charge ratio of ions. The results are presented as a '' mass spectrum'', a plot of intensity as a function of the mass-to-charge ratio. Mass spectrometry is us ...

Modeling

Models are essential tools for interpreting observational data, testing hypotheses about chemical reactions, and predicting future concentrations of atmospheric chemicals. To synthesize and test theoretical understanding of atmospheric chemistry, researchers commonly use computer models, such as chemical transport models (CTMs). CTMs provide realistic descriptions of the three-dimensional transport and evolution of the atmosphere.

Atmospheric models In atmospheric science, an atmospheric model is a mathematical model constructed around the full set of primitive, dynamical equations which govern atmospheric motions. It can supplement these equations with parameterizations for turbulent dif ...

can be seen as mathematical representations that replicate the behavior of the atmosphere. These numerical models solve the differential equations governing the concentrations of chemicals in the atmosphere. Depending on the complexity, these models can range from simple to highly detailed. Models can be zero-, one-, two-, or three-dimensional, each with various uses and advantages. Three-dimensional chemical transport models offer the most realistic simulations but require substantial computational resources. These models can be global e.g. GCM, simulating the atmospheric conditions across the Earth, or regional, e.g.

RAMS In engineering, reliability, availability, maintainability and safety (RAMS) A major challenge in atmospheric modeling is balancing the number of chemical compounds and reactions included in the model with the accuracy of physical processes such as transport and mixing in the atmosphere. Two simpliest types of models include box models and puff models. For example,

box modeling Box modeling is a technique in 3D modeling where a primitive shape (such as a box, cylinder, sphere, etc.) is used to make the basic shape of the final model. This basic shape is then used to sculpt out the final model. The process uses a number ...

is relatively simple and may include hundreds or even thousands of chemical reactions, but they typically use a very crude representation of atmospheric

mixed layer The oceanic or limnological mixed layer is a layer in which active turbulence has homogenized some range of depths. The surface mixed layer is a layer where this turbulence is generated by winds, surface heat fluxes, or processes such as evaporat ...

. This makes them useful for studying specific chemical reactions, but limited in stimulating real-world dynamics. In contrast,

3D models In 3D computer graphics, 3D modeling is the process of developing a mathematical coordinate-based representation of a surface of an object (inanimate or living) in three dimensions via specialized software by manipulating edges, vertices, and ...

are more complex, representing a variety of physical processes such as wind, convection, and atmospheric mixing. They also provide more realistic representations of transportation and mixing. However, computational limits often simply chemical reactions and typically include fewer chemical reactions than box models. The trade-off between the two approaches lies in resolution and complexity. To simplify the creation of these complex models, some researchers use automatic code generators like Autochem or

Kinetic PreProcessor The Kinetic PreProcessor (KPP) is an open-source software tool used in atmospheric chemistry. Taking a set of chemical reactions and their rate coefficients as input, KPP generates Fortran 90, FORTRAN 77, C, or Matlab code of the resulting or ...

. These tools help automate the model-building process by selecting relevant chemical reactions from databases based on a

user-defined function A user-defined function (UDF) is a function provided by the user of a program or environment, in a context where the usual assumption is that functions are built into the program or environment. UDFs are usually written for the requirement of its c ...

of chemical constituents. Once the reactions are chosen, the code generator automatically constructs the

ordinary differential equations In mathematics, an ordinary differential equation (ODE) is a differential equation (DE) dependent on only a single independent variable. As with any other DE, its unknown(s) consists of one (or more) function(s) and involves the derivatives ...

that describe their time evolution, greatly reducing the time and effort required for model construction. Differences between model prediction and real-world observations can arise from errors in model input parameters or flaws representations of processes in the model. Some input parameters like surface emissions are often less accurately quantified from observations compared to model results. The model can be improved by adjusting poorly known parameters to better match observed data. A formal method for applying these adjustments is through

Bayesian Optimization Bayesian optimization is a sequential design strategy for global optimization of black-box functions, that does not assume any functional forms. It is usually employed to optimize expensive-to-evaluate functions. With the rise of artificial intell ...

through an inverse modeling framework, where the results from the CTMs are inverted to optimize selected parameters. This approach has gained attention over the past decade as an effective method to interpret large amounts of data generate by models and observations from satellites. One important current trend is using atmospheric chemistry as part of Earth system models. These models integrate atmospheric chemistry with other Earth system components, enabling the study of complex interactions between climate, atmospheric composition, and ecosystems.

Applications

Atmospheric chemistry is a multidisciplinary field with wide-ranging applications that influence environmental policy, human health, technology development, and climate science. Examples of problems addressed in atmospheric chemistry include

acid rain Acid rain is rain or any other form of Precipitation (meteorology), precipitation that is unusually acidic, meaning that it has elevated levels of hydrogen ions (low pH). Most water, including drinking water, has a neutral pH that exists b ...

ozone depletion Ozone depletion consists of two related events observed since the late 1970s: a lowered total amount of ozone in Earth, Earth's upper atmosphere, and a much larger springtime decrease in stratospheric ozone (the ozone layer) around Earth's polar ...

greenhouse gasses Greenhouse gases (GHGs) are the gases in the atmosphere that raise the surface temperature of planets such as the Earth. Unlike other gases, greenhouse gases absorb the radiations that a planet emits, resulting in the greenhouse effect. T ...

and

global warming Present-day climate change includes both global warming—the ongoing increase in global average temperature—and its wider effects on Earth's climate system. Climate change in a broader sense also includes previous long-term changes ...

. By developing a theoretical understanding, atmospheric chemists can test potential solutions and evaluate the effects of changes in government policy. Key applications include

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 gas analyzer, infrared analyzing and ...

, air quality and pollution control, weather prediction and meteorology, energy and emissions, sustainable energy development, and public health and toxicology. Green atmospheric chemistry research prioritizes the sustainable, safe, and efficient use of chemicals, which led to government regulations minimizing the use of harmful chemicals like

CFCs Chlorofluorocarbons (CFCs) and hydrochlorofluorocarbons (HCFCs) are fully or partly halogenated hydrocarbons that contain carbon (C), hydrogen (H), chlorine (Cl), and fluorine (F). They are produced as volatile derivatives of methane, ethane, ...

and

DDT Dichlorodiphenyltrichloroethane, commonly known as DDT, is a colorless, tasteless, and almost odorless crystalline chemical compound, an organochloride. Originally developed as an insecticide, it became infamous for its environmental impacts. ...

. Advances in remote sensing technology allow scientists to monitor atmospheric chemical composition from satellites and ground-based stations. Instruments such as the Ozone Monitoring Instrument (OMI) and Atmospheric Infrared Sounder (AIRS) provide data on pollutants, greenhouse gasses, and aerosols, enabling real-time monitoring of air quality. Atmospheric chemistry is vital for evaluating the environmental impacts of energy production, including fossil fuels and renewable energy sources. By studying emissions, researchers can develop cleaner energy technologies and assess their effects on air quality and climate. Atmospheric chemistry also helps quantify the concentration and persistence of toxic substances in the air, including

particulate matter Particulate matter (PM) or particulates are microscopic particles of solid or liquid matter suspended in the air. An ''aerosol'' is a mixture of particulates and air, as opposed to the particulate matter alone, though it is sometimes defin ...

and volatile organic compounds (VOCs), guiding public health measures and exposures assessments.

References

External links

WMO Scientific Assessment of Ozone Depletion: 2006

IGAC The International Global Atmospheric Chemistry Project

Paul Crutzen Interview
- freeview video of

Nobel Laureate for his work on decomposition of ozone, talking to Nobel Laureate

Harry Kroto Sir Harold Walter Kroto (born Harold Walter Krotoschiner; 7 October 1939 – 30 April 2016) was an English chemist. He shared the 1996 Nobel Prize in Chemistry with Robert Curl and Richard Smalley for their discovery of fullerenes. He was t ...

, the Vega Science Trust
The Cambridge Atmospheric Chemistry Database
is a large constituent observational database in a common format.

* ttp://jpldataeval.jpl.nasa.gov/index.html NASA-JPL Chemical Kinetics and Photochemical Data for Use in Atmospheric Studies
Kinetic and photochemical data evaluated by the IUPAC Subcommittee for Gas Kinetic Data Evaluation

{{Branches of chemistry

Atmospheric Chemistry Atmospheric chemistry is a branch of atmospheric science that studies the chemistry of the Earth's atmosphere and that of other planets. This multidisciplinary approach of research draws on environmental chemistry, physics, meteorology, comput ...

Environmental chemistry Chemistry