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Air Pollutants
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N2O
Nitrous oxide is a non-toxic gas that can also be referred to as “laughing gas” and has found use both as a fuel additive and anesthetic (drug for pain reduction). Nitrous oxide is also a common byproduct of the microbial breakdown of nitrogen-based compounds from organic matter within the oceans and soil. It has both natural and man-made sources in the environment, with the percent contribution from each being 57% and 43% respectively, according to a 2020 study. Regarding the 57% that is natural, the predominant sources are from the soil and ocean, where fungi and certain types of bacteria are the main producers of it. Nitrification and denitrification are two biochemical processes that control the amount of nitrous oxide being released into the atmosphere.
Nitrification: The natural conversion of ammonium (NH4) to nitrate (NO3) due to microbiological processes in the environment from bacteria and fungi
Denitrification: The natural conversion of nitrate (NO3) to nitrogen gas (N2) due to microbiological processes in the environment from bacteria and fungi
In the above image, numbers represent the average amount of nitrogen being released in units of Terra grams (1,000,000,000,000 grams of nitrogen) from the years of 2010-2019
Referring to the 43% of nitrous oxide that is man-made, these sources primarily come from the agricultural industry and fossil fuel use. The nitrous oxide concentration in the atmosphere has increased by over 20% from 1750 – 2018 and is largely due to the production of synthetic nitrogen fertilizers for the agricultural industry. More specifically, an industrial process called the Haber-Bosch process, which allowed for the conversion of nitrogen in the atmosphere into ammonia, which is used in fertilizers to more efficiently grow crops.
Nitrous oxide is harmful to the environment due to it being a strong green house gas and contributing to climate change. It has a Global Warming Potential (GWP) of 273, making it an important contributor to the warming of the planet. Currently, the atmospheric concentration of nitrous oxide is 337 parts per billion, about a 7% increase from the early 2000s
CO2
Carbon dioxide is a commonly occurring gas within the environment and can come from both natural and man-made sources. However, CO2 can be freely changed/converted into other molecules when interacting with certain environments, allowing it to be easily transported between the air, water and rocks. As an example, CO2 begins in the atmosphere, making up 0.04% of the gasses present, originating from sources such as the burning of fossil fuels (e.g. transportation, heating, industrial use) and also human and animal respiration. CO2 can then be absorbed by plants at the surface, transforming it into glucose (sugar) as an energy source. Additionally, CO2 can be dissolved into rainwater as it is falling, creating acid rain due to the formation of H2CO3. (carbonic acid). Both these processes allow atmospheric CO2 to be transferred from the atmosphere to the earth’s surface. Acid rain can further interact with exposed rocks on the surface that contain carbon within them (silicate and carbonate rocks). The acid rain erodes/weathers these rocks and in turn allows carbon molecules within the rock to be transferred into the rainwater, forming Dissolved Inorganic Carbon (DIC).
Dissolved Inorganic Carbon: “Dissolved” – carbon that has mixed with water creating a homogenous solution, “Inorganic Carbon” – carbon atoms that do not contain chemical bonds to hydrogen
This rainwater that now contains carbon from both the atmosphere and exposed rocks can be stored within streams, lakes, or oceans. Consequently, this acts as a control on the amount of CO2 that is released to the atmosphere, since the carbon within rocks can alternatively be released to the air due to oxidation processes.
In the above image, numbers represent the average amount of carbon dioxide being released in units of Peta grams (1,000,000,000 grams of carbon dioxide) from the year 2023
Carbon dioxide can be harmful to the environment if there are excess concentrations of it within the atmosphere, since CO2 is an abundant greenhouse gas. It has a Global Warming Potential of 1, meaning it has a low potency as a greenhouse gas, however, it makes up 76% of the total amount of greenhouse gases in the atmosphere making it a strong concern due to its high concentration. Health impacts from carbon dioxide exposure can vary depending on the exposure time and concentration. Prolonged exposure indoors has shown to cause health impacts such as drowsiness, headaches, or heart rate variation, in which these symptoms may occur at a CO2 concentration above 1,000 parts per million (ppm). However, exposure at CO2 concentrations of 40,000, 50,000, or 70,000 ppm can be fatal or cause intoxication.
Currently, the atmospheric concentration of carbon dioxide is 422 parts per million, a 35% increase since 1960.
Particulate Matter
Particulate matter refers to the presence of small solid and liquid particulate within the air and is typically characterized based on the size of the particulates, with PM 10, PM 2.5, and PM 1 referring to particulates that are smaller than 10 micro metres, 2.5 micro metres, and 1 micro metre.
Larger particulate (PM10) typically originates from natural sources such as dust storms, forest fire ash, or pollen grains, which commonly have more coarse particulates. Smaller particulates (PM 2.5, PM 1) typically originate from man-made sources such as traffic or industrial emissions. As an example, heavy metals from vehicles release particulate matter due to zinc or copper metal being shaved off from brake linings, although these particulates may vary in size.
Particulate matter is a climate change driver and can have impacts on atmospheric processes such as cloud formation or the amount of sunlight and radiation that reaches the earth’s surface. Additionally, once particulates deposit on plant material it can reduce the plant photosynthesis processes due to particulate residue on plant leaves blocking sunlight. Furthermore, particulate matter acts as a reaction surface for contaminants to bind and be transported to alternative environments. For example, binding of a contaminant to a particulate and being deposited in a soil environments can have adverse effects on the biogeochemical processes that occur within the soil. Particulate matter also has adverse effects on humans, with PM10 constituents causing respiratory and circulatory issues leading to heart disease/defects, DNA damage, developmental issues with fetus growth, and cancer risk.