Major Air Pollutants 1
Particulate Matter Particulate refers to all substances that are not gases. It can be suspended droplets / solid particles / mixture of two. Size: 100 µm to 0.1 µm and less. Particulates can be composed of inert or extremely reactive material. Inert material does not react readily with environment whereas the reactive material could be further oxidized or may react chemically with environment. 2
Particulates introduced directly into the air can originate from: Natural fires Volcanic eruptions The ejection of salt crystals by breaking ocean waves By entrainment of pollen by wind Human activities especially those involving combustion Produce primary and secondary particulates. Process of coagulation is responsible for the formation of some secondary particulates. This process is most rapid when the air humidity is high. 3
Classification of particulates matter Dust It contains particles of the size ranging from 1 to 200 µm. These are formed by natural disintegration of rock and soil or by the mechanical processes of grinding and spraying. They have large settling velocities and are removed from the air by gravity and other inertial processes. Fine dust particles act as centers of catalysis for many of the chemical reaction-taking place in the atmosphere. 4
Smoke It contains fine particles of the size ranging from 0.01 to 1 µm which can be liquid or solid and are formed by combustion or other chemical processes. May have different color depending on the nature of material burnt. 5
Fumes It is consisted of the particles formed by condensation, sublimation or chemical reaction of which the predominant part consists of particles ranging from 0.1 µm to 1 µm in size. Released from chemical or metallurgical processes. e.g. tobacco smoke, condensed metal oxides 6
Mist It is a low concentration dispersion of relatively small droplets in air smaller than 10µm. Mist may result from the condensation of gases or vapors to liquid state. They can also be formed by breaking up a liquid through splashing, spraying or foaming. 7
Fog It is the mist in which the liquid in water and dense to obscure vision. Aerosols These are solids or liquids of microscopic size dispersed in gaseous media smaller than 1 µm. e.g. Smoke, fog or mist 8
Carbon oxides (CO & CO 2 ) CO (carbon monoxide) is a tasteless, colorless and odorless gas with slightly lesser density than air. Sources: Incomplete combustion of fossil fuels and other carbonaceous matter, some industrial processes, solid waste combustion, cigarette smoke, transportation Natural source: Volcanoes, lightening and photochemical degradation of some reactive organic compounds. CO is also formed biologically by certain brown algae, various microorganisms and also some oceanic organisms. 9
The mean residence time: 1 month to 5 years Effects: Combines with hemoglobin (reduce the normal capacity of blood to transport oxygen to the tissue) & may create problems for infants, the elderly & those with heart or respiratory diseases. At higher concentration of 100 ppm it may cause people to experience dizziness, headache, lassitude and other symptoms A concentration of 4000 ppm is lethal in less than one hour. 75.1 % CO is produced by total fuel combustion, 7.7 % from industrial processes, 9.3 % from agricultural burning, 4.9 % from solid waste disposal and 3 % from miscellaneous sources. 10
CO 2 (Carbon Dioxide) It is not a typical air pollutant. It is greenhouse gas Sources: Decay of organic matter and respiration of organisms. Combustion of fossil fuels such as coal, oil and natural gas About half of the excessive quantities discharged into the atmosphere are absorbed by the oceans while much are utilized in photosynthesis. 11
Sulfur oxides (SO 2, SO 3 ): SO 2 (Sulphur dioxide): SO 2 is a colorless gas processing a pungent and irritation odour at higher concentration above 300 ppm. Source Smelting, combustion of coal & oil (esp. coal) Ores of Cu, Zn, Pb and Ni etc. contain as much as 10 % or more of sulphur. Lifetime: 2 to 4 days 12
Effects: It can react with gases in atmosphere to form sulfuric acid ('acid rain') 20 million tons released in U.S. every year Exposure to SO 2 can cause impairment of respiratory function, aggravation of existing respiratory disease (especially bronchitis), Decrease in the ability of the lungs to clear foreign particles. It can also lead to increased mortality, especially if elevated levels of particulate matter (PM) are also present. 13
SO 2 (Sulphur dioxide): Groups that appear most sensitive to the effects of SO 2 include asthmatics and other individuals with hyperactive airways and individuals with chronic obstructive lung or cardiovascular disease. Elderly people and children are also likely to be more sensitive to SO 2. 14
SO 2 released in the U.S. comes from: Utilities 69.5% Industrial manufacturing processes 12.7% Industrial combustion 11.6% Transportation 3.7% Other sources 2.5%. Sulphur trioxide (SO 3 ) Sulphur trioxide is formed by oxidation of sulphur dioxide. It may exits in the form of vapor and readily combines with water to form H 2 SO 4. Source: Combustion of sulphur containing material 15
Nitrogen oxides NO x : The most abundant and important oxides of nitrogen forming air pollutants are Nitric Oxide (NO), Nitrogen Dioxide (NO 2 ), Nitrous oxide (N 2 O) Lifetime: Less than 2 days Nitric Oxide: It is colorless and relatively harmless gas, but its get readily converted into NO 2 by photochemical reactions. Source: High temperature combustion, motor vehicles (40 % of NOx discharge) & industry, biologically in nature 16
Nitrogen Dioxide: It is reddish brown gas with pungent odor. The gas is corrosive, irritating and physiologically toxic. It reacts with water to form nitric acid, which may be a significant component of acid rain. It is formed primarily by photo oxidation of NO. Its fate is oxidation to nitric acid, nitrates or photo dissociation 17
Ammonia (NH 3 ) It is a colorless, pungent, suffocating and highly soluble gas in water. 99.9 % NH 3 is released from the natural sources during degradation of organic matter. Source: combustion of fuels in stationary and mobile sources, incineration of wastes, fertilizer plants, Chemical plants, coke ovens, refineries Lifetime: 6 days Its fate is conversion to ammonium salts 18
Hydrogen Sulphide (H 2 S): It is a colorless gas with a foul odor. Source: Natural processes (Bacterial decomposition of organic matter, sulphur deposits, volcanic gases and sulphur springs) Industries such as Kraft paper mills, petroleum refineries, coke oven plants, and sewage and industrial waste disposal ponds. Residence time: 4.4 days Effects: The gas at higher concentration is toxic to human and animals. It may also corrosive to the metals 19
Hydrogen Chloride (HCl): It is a colorless, strong, pungent and irritating gas with a high solubility in water. Source: Natural: Volcanic fumes, rivers Burning of paper products or chlorine containing materials, Chemical Industries also produced HCl as a byproduct Effects: It is great soluble in water producing fumes of hydrochloric Acid in moist air. Hydrochloric acid is extremely injurious to the skin and mucous membranes. 20
Hydrocarbons: It is Volatile organic compounds (hydrocarbons) - methane, benzene, propane, & chlorofluorocarbons (CFC's) Sources: Motor vehicles (evaporation from gas tanks), industry, & various household products 18 million tons released each year in U.S. Concentrations of many VOCs are consistently higher indoors than outdoors. 21
Hydrocarbons: Effects: Eye and respiratory tract irritation, headaches, dizziness, visual disorders, and memory impairment are among the immediate symptoms that some people have experienced soon after exposure to some organics. Many organic compounds are known to cause cancer in animals; some are suspected of causing, or are known to cause, cancer in humans. 22