Trace gases are gases that are present in small amounts within an environment such as a planet's atmosphere. Trace gases in Earth's atmosphere are gases other than nitrogen (78.1%), oxygen (20.9%), and argon (0.934%) which, in combination, make up 99.934% of its atmosphere (not including water vapor).
The abundance of a trace gas can range from a few parts per trillion (ppt) by volume to several hundred parts per million by volume (ppmv). [1] When a trace gas is added into the atmosphere, that process is called a source. There are two possible types of sources - natural or anthropogenic. Natural sources are caused by processes that occur in nature. In contrast, anthropogenic sources are caused by human activity.
Some sources of a trace gas are biogenic processes, outgassing from solid Earth, ocean emissions, industrial emissions, and in situ formation. [1] A few examples of biogenic sources include photosynthesis, animal excrements, termites, rice paddies, and wetlands. Volcanoes are the main source for trace gases from solid earth. The global ocean is also a source of several trace gases, in particular sulfur-containing gases. In situ trace gas formation occurs through chemical reactions in the gas-phase. [1] Anthropogenic sources are caused by human related activities such as fossil fuel combustion (e.g. in transportation), fossil fuel mining, biomass burning, and industrial activity.
In contrast, a sink is when a trace gas is removed from the atmosphere. Some of the sinks of trace gases are chemical reactions in the atmosphere, mainly with the OH radical, gas-to-particle conversion forming aerosols, wet deposition and dry deposition. [1] Other sinks include microbiological activity in soils.
Below is a chart of several trace gases including their abundances, atmospheric lifetimes, sources, and sinks.
Trace gases – taken at pressure 1 atm [1]
Gas | Chemical formula | Fraction of volume of air by the species | Residence time or lifetime | Major sources | Major sinks |
---|---|---|---|---|---|
Carbon dioxide | CO2 | 419 ppm ≈ppmv (May, 2021) [2] | Increasing, See Note [A] | Biological, oceanic, combustion, anthropogenic | photosynthesis |
Neon | Ne | 18.18 ppmv | _________ | Volcanic | ________ |
Helium | He | 5.24 ppmv | _________ | Radiogenic | ________ |
Methane | CH4 | 1.89 ppm (May, 2021) [3] | 9 years | Biological, anthropogenic | OH |
Hydrogen | H2 | 0.56 ppmv | ~ 2 years | Biological, HCHO photolysis | soil uptake |
Nitrous oxide | N2O | 0.33 ppmv | 150 years | Biological, anthropogenic | O(1D) in stratosphere |
Carbon monoxide | CO | 40 – 200 ppbv | ~ 60 days | Photochemical, combustion, anthropogenic | OH |
Ozone | O3 | 10 – 200 ppbv (troposphere) | Days – months | Photochemical | photolysis |
Formaldehyde | HCHO | 0.1 – 10 ppbv | ~ 1.5 hours | Photochemical | OH, photolysis |
Nitrogen species | NOx | 10 pptv – 1 ppmv | Variable | Soils, anthropogenic, lightning | OH |
Ammonia | NH3 | 10 pptv – 1 ppbv | 2 – 10 days | Biological | gas-to-particle conversion |
Sulfur dioxide | SO2 | 10 pptv – 1 ppbv | Days | Photochemical, volcanic, anthropogenic | OH, water-based oxidation |
Dimethyl sulfide | (CH3)2S | several pptv – several ppbv | Days | Biological, ocean | OH |
A The Intergovernmental Panel on Climate Change (IPCC) states that "no single atmospheric lifetime can be given" for CO2. [4] : 731 This is mostly due to the high rate of growth and large cumulative magnitude of the disturbances to Earth's carbon cycle by the geologic extraction and burning of fossil carbon. [5] As of year 2014, fossil CO2 emitted as a theoretical 10 to 100 GtC pulse on top of the existing atmospheric concentration was expected to be 50% removed by land vegetation and ocean sinks in less than about a century. [6] A substantial fraction (20-35%) was also projected to remain in the atmosphere for centuries to millennia, where fractional persistence increases with pulse size. [7] [8] Thus CO2 lifetime effectively increases as more fossil carbon is extracted by humans.
The overall abundance of man-made trace gases in Earth's atmosphere is growing. Most originate from industrial activity in the more populated northern hemisphere. Time-series data from measurement stations around the world indicate that it typically takes 1–2 years for their concentrations to become well-mixed throughout the troposphere. [9] [10]
The residence time of a trace gas depends on the abundance and rate of removal. The Junge (empirical) relationship describes the relationship between concentration fluctuations and residence time of a gas in the atmosphere. It can expressed as fc = b/τr, where fc is the coefficient of variation, τr is the residence time in years, and b is an empirical constant, which Junge originally gave as 0.14 years. [11] As residence time increases, the concentration variability decreases. This implies that the most reactive gases have the most concentration variability because of their shorter lifetimes. In contrast, more inert gases are non-variable and have longer lifetimes. When measured far from their sources and sinks, the relationship can be used to estimate tropospheric residence times of gases. [11]
A few examples of the major greenhouse gases are water, carbon dioxide, methane, nitrous oxide, ozone, and CFCs. These gases can absorb infrared radiation from the Earth's surface as it passes through the atmosphere.
The most influential greenhouse gas is water vapor. It frequently occurs in high concentrations, may transition to and from an aerosol (clouds), and is thus not generally classified as a trace gas. Regionally, water vapor can trap up to 80 percent of outgoing IR radiation. [12] Globally, water vapor is responsible for about half of Earth's total greenhouse effect. [13]
The second most important greenhouse gas, and the most important trace gas affected by man-made sources, is carbon dioxide. [12] It contributes about 20% of Earth's total greenhouse effect. [13] The reason that greenhouse gases can absorb infrared radiation is their molecular structure. For example, carbon dioxide has two basic modes of vibration that create a strong dipole moment, which causes its strong absorption of infrared radiation. [12]
In contrast, the most abundant gases (N
2,O
2, and Ar) in the atmosphere are not greenhouse gases. This is because they cannot absorb infrared radiation as they do not have vibrations with a dipole moment. [12] For instance, the triple bonds of atmospheric dinitrogen make for a symmetric molecule with vibrational energy states that are almost totally unaffected at infrared frequencies.
Below is a table of some of the major trace greenhouse gases, their man-made sources, and an estimate of the relative contribution of those sources to the enhanced greenhouse effect that influences global warming.
Key Greenhouse Gases and Sources [12]
Gas | Chemical formula | Major human sources | Contribution to Increase (Year 1995 estimate) |
---|---|---|---|
Carbon dioxide | CO2 | fossil fuel combustion, deforestation | 55% |
Methane | CH4 | rice fields, cattle and dairy cows, landfills, oil and gas production | 15% |
Nitrous oxide | N2O | fertilizers, deforestation | 6% |
Carbon dioxide is a chemical compound with the chemical formula CO2. It is made up of molecules that each have one carbon atom covalently double bonded to two oxygen atoms. It is found in the gas state at room temperature, and as the source of available carbon in the carbon cycle, atmospheric CO2 is the primary carbon source for life on Earth. In the air, carbon dioxide is transparent to visible light but absorbs infrared radiation, acting as a greenhouse gas. Carbon dioxide is soluble in water and is found in groundwater, lakes, ice caps, and seawater. When carbon dioxide dissolves in water, it forms carbonate and mainly bicarbonate, which causes ocean acidification as atmospheric CO2 levels increase.
The greenhouse effect occurs when greenhouse gases in a planet's atmosphere trap some of the heat radiated from the planet's surface, raising its temperature. This process happens because stars emit shortwave radiation that passes through greenhouse gases, but planets emit longwave radiation that is partly absorbed by greenhouse gases. That difference reduces the rate at which a planet can cool off in response to being warmed by its host star. Adding to greenhouse gases further reduces the rate a planet emits radiation to space, raising its average surface temperature.
Global warming potential (GWP) is an index to measure of how much infrared thermal radiation a greenhouse gas would absorb over a given time frame after it has been added to the atmosphere. The GWP makes different greenhouse gases comparable with regards to their "effectiveness in causing radiative forcing". It is expressed as a multiple of the radiation that would be absorbed by the same mass of added carbon dioxide, which is taken as a reference gas. Therefore, the GWP is one for CO2. For other gases it depends on how strongly the gas absorbs infrared thermal radiation, how quickly the gas leaves the atmosphere, and the time frame being considered.
The atmosphere of Earth is the layer of gases, known collectively as air, retained by Earth's gravity that surrounds the planet and forms its planetary atmosphere. The atmosphere of Earth creates pressure, absorbs most meteoroids and ultraviolet solar radiation, warms the surface through heat retention, and reduces temperature extremes between day and night, maintaining conditions allowing life and liquid water to exist on the Earth's surface.
Radiative forcing is the change in energy flux in the atmosphere caused by natural or anthropogenic factors of climate change as measured in watts per meter squared. It is a scientific concept used to quantify and compare the external drivers of change to Earth's energy balance. These external drivers are distinguished from climate feedbacks and internal variability, which also influence the direction and magnitude of imbalance.
This glossary of climate change is a list of definitions of terms and concepts relevant to climate change, global warming, and related topics.
The Keeling Curve is a graph of the accumulation of carbon dioxide in the Earth's atmosphere based on continuous measurements taken at the Mauna Loa Observatory on the island of Hawaii from 1958 to the present day. The curve is named for the scientist Charles David Keeling, who started the monitoring program and supervised it until his death in 2005.
The infrared atmospheric window refers to a region of the infrared spectrum where there is relatively little absorption of terrestrial thermal radiation by atmospheric gases. The window plays an important role in the atmospheric greenhouse effect by maintaining the balance between incoming solar radiation and outgoing IR to space. In the Earth's atmosphere this window is roughly the region between 8 and 14 μm although it can be narrowed or closed at times and places of high humidity because of the strong absorption in the water vapor continuum or because of blocking by clouds. It covers a substantial part of the spectrum from surface thermal emission which starts at roughly 5 μm. Principally it is a large gap in the absorption spectrum of water vapor. Carbon dioxide plays an important role in setting the boundary at the long wavelength end. Ozone partly blocks transmission in the middle of the window.
This is a list of the most influential long-lived, well-mixed greenhouse gases, along with their tropospheric concentrations and direct radiative forcings, as identified by the Intergovernmental Panel on Climate Change (IPCC). Abundances of these trace gases are regularly measured by atmospheric scientists from samples collected throughout the world. Since the 1980s, their forcing contributions are also estimated with high accuracy using IPCC-recommended expressions derived from radiative transfer models.
In climate science, longwave radiation (LWR) is electromagnetic thermal radiation emitted by Earth's surface, atmosphere, and clouds. It may also be referred to as terrestrial radiation. This radiation is in the infrared portion of the spectrum, but is distinct from the shortwave (SW) near-infrared radiation found in sunlight.
Greenhouse gas (GHG) emissions from human activities intensify the greenhouse effect. This contributes to climate change. Carbon dioxide, from burning fossil fuels such as coal, oil, and natural gas, is one of the most important factors in causing climate change. The largest emitters are China followed by the United States. The United States has higher emissions per capita. The main producers fueling the emissions globally are large oil and gas companies. Emissions from human activities have increased atmospheric carbon dioxide by about 50% over pre-industrial levels. The growing levels of emissions have varied, but have been consistent among all greenhouse gases. Emissions in the 2010s averaged 56 billion tons a year, higher than any decade before. Total cumulative emissions from 1870 to 2017 were 425±20 GtC from fossil fuels and industry, and 180±60 GtC from land use change. Land-use change, such as deforestation, caused about 31% of cumulative emissions over 1870–2017, coal 32%, oil 25%, and gas 10%.
The atmospheric infrared sounder (AIRS) is one of six instruments flying on board NASA's Aqua satellite, launched on May 4, 2002. The instrument is designed to support climate research and improve weather forecasting.
In Earth's atmosphere, carbon dioxide is a trace gas that plays an integral part in the greenhouse effect, carbon cycle, photosynthesis and oceanic carbon cycle. It is one of several greenhouse gases in the atmosphere of Earth. The current global average concentration of CO2 in the atmosphere is 421 ppm as of May 2022 (0.04%). This is an increase of 50% since the start of the Industrial Revolution, up from 280 ppm during the 10,000 years prior to the mid-18th century. The increase is due to human activity. Burning fossil fuels is the main cause of these increased CO2 concentrations and also the main cause of climate change. Other large anthropogenic sources include cement production, deforestation, and biomass burning.
The Global Carbon Project (GCP) is an organisation that seeks to quantify global greenhouse gas emissions and their causes. Established in 2001, its projects include global budgets for three dominant greenhouse gases—carbon dioxide, methane, and nitrous oxide —and complementary efforts in urban, regional, cumulative, and negative emissions.
Greenhouse gases are the gases in the atmosphere that raise the surface temperature of planets such as the Earth. What distinguishes them from other gases is that they absorb the wavelengths of radiation that a planet emits, resulting in the greenhouse effect. The Earth is warmed by sunlight, causing its surface to radiate heat, which is then mostly absorbed by water vapor (H2O), carbon dioxide (CO2), methane (CH4), nitrous oxide (N2O), and ozone (O3). 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).
Atmospheric methane is the methane present in Earth's atmosphere. The concentration of atmospheric methane is increasing due to methane emissions, and is causing climate change. Methane is one of the most potent greenhouse gases. Methane's radiative forcing (RF) of climate is direct, and it is the second largest contributor to human-caused climate forcing in the historical period. Methane is a major source of water vapour in the stratosphere through oxidation; and water vapour adds about 15% to methane's radiative forcing effect. The global warming potential (GWP) for methane is about 84 in terms of its impact over a 20-year timeframe. That means it traps 84 times more heat per mass unit than carbon dioxide (CO2) and 105 times the effect when accounting for aerosol interactions.
The history of the scientific discovery of climate change began in the early 19th century when ice ages and other natural changes in paleoclimate were first suspected and the natural greenhouse effect was first identified. In the late 19th century, scientists first argued that human emissions of greenhouse gases could change Earth's energy balance and climate. The existence of the greenhouse effect, while not named as such, was proposed as early as 1824 by Joseph Fourier. The argument and the evidence were further strengthened by Claude Pouillet in 1827 and 1838. In 1856 Eunice Newton Foote demonstrated that the warming effect of the sun is greater for air with water vapour than for dry air, and the effect is even greater with carbon dioxide.
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 from space such as by the Orbiting Carbon Observatory and networks of ground stations such as the Integrated Carbon Observation System.
The atmospheric carbon cycle accounts for the exchange of gaseous carbon compounds, primarily carbon dioxide, between Earth's atmosphere, the oceans, and the terrestrial biosphere. It is one of the faster components of the planet's overall carbon cycle, supporting the exchange of more than 200 billion tons of carbon in and out of the atmosphere throughout the course of each year. Atmospheric concentrations of CO2 remain stable over longer timescales only when there exists a balance between these two flows. Methane, Carbon monoxide (CO), and other man-made compounds are present in smaller concentrations and are also part of the atmospheric carbon cycle.