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Ammonia is a colourless gas with a characteristic pungent smell. Ammonia contributes significantly to the nutritional needs of terrestrial organisms by serving as a precursor to food and fertilizers. Ammonia is also used for the synthesis of many pharmaceuticals and in cleaning products.

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Carbon Monoxide

During incomplete combustion of fossil fuels part of the carbon is not completely oxidized, producing CO. The largest source of CO is natural in origin, due to photochemical reactions in the troposphere. Other natural sources of CO include volcanoes, forest fires, and other forms of combustion.

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Low Level (tropospheric) Ozone

Low level ozone (or tropospheric ozone) is an atmospheric pollutant. It is not emitted directly into the air, but is created by chemical reactions between oxides of nitrogen (NOx) and volatile organic compounds (VOC) in the presence of sunlight. Emissions from industrial facilities and electric utilities, motor vehicle exhaust, gasoline vapors, and chemical solvents are some of the major sources of NOx and VOC. The atmospheric lifetime of tropospheric ozone is about 22 days; its main removal mechanisms are being deposited to the ground.

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Methane is a colorless, odorless gas that is widely found in nature. It can be produced by the decomposition of plant and animal matter and is prevalent near landfills. Methane is also one of the principal components in natural gas. It is second only to carbon dioxide in its contribution to global warming.

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NOx is a generic term for the mono-nitrogen oxides NO and NO2. They are produced from the reaction among nitrogen, oxygen and even hydrocarbons (during combustion), especially at high temperatures. NO2 is the main source of nitrate aerosols, which form an important fraction of PM2.5 and, in the presence of ultraviolet light, of ozone. The major sources of anthropogenic emissions of NO2 are combustion processes (heating, power generation, and engines in vehicles and ships). NOx gases react to form smog and acid rain as well as being central to the formation of tropospheric ozone.

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Particulate Matter

Particulate Matter (PM) is a complex mixture of extremely small particles and liquid droplets. They including acids (such as nitrates and sulfates), organic chemicals, metals, and soil or dust particles, ammonia, sodium chloride, black carbon, mineral dust and water. "Inhalable coarse particles," such as those found near roadways and dusty industries, are larger than 2.5 microns and smaller than 10 microns.

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Sulphur dioxide

Sulphur dioxide (SO2) is one of a group of highly reactive gasses known as “oxides of sulphur.” The largest sources of SO2 emissions are from fossil fuel combustion at power plants (73%) and other industrial facilities (20%). Smaller sources of SO2 emissions include industrial processes such as extracting metal from ore, and the burning of high sulphur containing fuels by locomotives, large ships, and non-road equipment. When SO2 combines with water, it forms sulphuric acid; this is the main component of acid rain which is a cause of deforestation.

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VOC and HAP stand for Volatile Organic Compound and Hazardous Air Pollutant respectively. VOCs are numerous, varied, and ubiquitous. They include both human-made and naturally occurring chemical compounds. The majority of scents or odours are composed of VOCs.

Hazardous Air Pollutants are those pollutants that cause or may cause cancer or other serious health effects, such as reproductive effects or birth defects, or adverse environmental and ecological effects.

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