A1r Pollutants

A1R POLLUTANTS hundreds of materials are discharged into the atmosphere as a result of human activities. Those that Produce adverse health or environmental effects are termed air pollutants.

A1R POLLUTANTS • Air pollutant may be classified as primary pollutants, which are released directly into air in a harmful form; or secondary pollutants, which are modified into a hazardous form after they enter the atmosphere due to chemical reactions or which are formed in the atmosphere.

A1R POLLUTANTS • There are many pollutants with serious harm in the air, they come from burning of fuel, waste gases from industry and vehicle.

A1R POLLUTANTS • The typical primary pollutants are carbon monoxide, hydrocarbons, particulates, sulfur dioxide, and nitrogen compounds. Examples of secondary pollutants are photochemical oxidants and atmospheric acids formed in the atmosphere due to solar energy-activated reactions of less harmful materials.

A1R POLLUTANTS • The Clean Air Act of l970 designated seven major pollutants as conventional or criteria pollutants because of their serious threat to public health and environmental quality. These include carbon monoxide, hydrocarbons, sulfur dioxide, particulates, nitrogen oxides, photochemical oxidants, and lead.

arbon monoxide (CO) • It is a colorless, odorless, nonirritating poison that can quickly cause death at quite low concentrations. Inhaled carbon monoxide will tightly attach to hemoglobin in blood, reducing the capacity of the blood to carry oxygen to bodily tissues. The result is headaches, drowsiness, and eventually asphyxiation.

arbon monoxide (CO) • Carbon monoxide is produced when organic materials such as gasoline, coal, or wood are incompletely burned. The automobile is responsible for most of the carbon monoxide produced in cities (67 percent), but stationary fuel combustion (20 percent) and industrial processes (6 percent) also contribute.

Hydrocarbons • They constitute a large group of volatile organic compounds. The major anthropogenic sources of hydrocarbons emitted to the atmosphere are evaporation of petroleum-based fuels and remnants of the fuels that did not burn completely.

Hydrocarbons • The automobile is the major source of hydrocarbons, followed by refineries and other industries. About 28 million tons of these materials are emitted annually in the United States.

Hydrocarbons • In addition to naturally occurring hydrocarbons, many synthetic organic compounds are also emitted, including benzene, toluene, formaldehyde, vinyl chloride, phenols, and trichloroethylene.

Hydrocarbons • These total over 2.5 million metric tons per year. some of these are carcinogenic and others contribute to other health--related problems. The most significant impact of airborne hydrocarbons, though, is the part they play in the formation of ozone in the lower atmosphere, as described later chapter

Sulfur dioxide (SO2) • It is formed when fuel containing sulfur (mainly coal and oil) is burned, and during metal smelting and other industrial processes. Major health concerns associated with exposure to high concentrations of SO2 include effects on breathing, respiratory illness, alterations in pulmonary defenses, and aggravation of existing cardiovascular disease.

Sulfur dioxide (SO2) It is a colorless corrosive gas that is a respiratory irritant and a poison. It is also of major concern because it can react in the atmosphere with ozone, water vapor, and other materials to form sulfuric acid (H2SO4). Sulfuric acid, one of the strongest oxidizing agents known, can cause substantial damage to construction materials, metals, and other materials.

Sulfur dioxide (SO2) It can also forms very small aerosols or attach to minute aerosols, which can travel deep into the respiratory system when inhaled, doing serious tissue damage.

Sulfur dioxide (SO2) • The major anthropogenic sources of sulfur dioxide emissions to the atmosphere are combustion of sulfur-containing fuels (coal and oil) and industrial Processes. More than 70 percent of the sulfur dioxide in our air in urban areas comes from coal-burning electrical power plants.

Particulates They are small pieces of solid or liquid materials dispersed in the atmosphere, constitute the third largest category of air pollutant. These include dust, ash, soot, smoke, and droplets of pollutants either emitted to the air or formed in the atmosphere.

Particulates They are characterized as 0.005 to l00um in size. The major human sources of particulates are from unburned fuels from stationary fuel combustion and transportation as well as industrial Processes.

Particulates • The impacts of particulates range from reduced visibility and soiling of exposed surfaces to respiratory problems and carcinogen city.

Repairable particles • Repairable particles (smaller than 2.5 um) are especially Problematic because they can be drawn deep into the lungs, where they can damage respiratory tissues. Because of their small size (80 percent are less than 2.5 um), particulates from vehicles are particularly insidious. Hydrocarbons are also of major concern because they can participate in photochemical reactions producing smog, as will be described later .more.

rogen Oxides (NO and NO2) • They are highly reactive gases formed from oxidation of the nitrogen in air during combustion. When combustion takes place in air at a temperature above about 2000 degree

Nitrogen Oxides (NO and NO2)

• Fahrenheit the nitrogen and oxygen molecules in air may react with each other forming oxides of nitrogen: 2NO (nitrogen oxide) • N 2 + O2 • 2NO + O2

2NO2 (nitrogen dioxide)

Nitrogen Oxides (NO and NO2)

• The designation NOx is often used to signify mixtures of NO and NO2 in air .the nitrogen dioxide is a critical component in smog-forming reactions.

Nitrogen Oxides (NO and NO2) • Nitrogen oxides can also react with water vapor, forming nitric acid (HNO3), and contribute to acid precipitation problems. The primary source of NOx is the automobile engine, although combustion of coal, oil, or natural gas at high enough temperatures can also contribute to the problem.

rogen Oxides (NO and NO2) • Ironically, an excellent way to minimize emissions of hydrocarbons and carbon monoxide is to burn fuels at high temperatures with an abundance of air, but this then increases the amount of NOx emitted.

hotochemical oxidants • They are products of secondary atmospheric reactions driven by solar energy. One of the most important of these is ozone (O3).

Photochemical oxidants

• Ozone is a strong oxidant and can destroy lung tissue and chlorophyll in plants. It will be described in detail in the next chapter. Other photochemical oxidants include peroxyacetal nitrate (PAN) and acrolein, both of which are strong oxidants and can damage materials. PAN is also a severe eye irritant.

ead and other volatile metals • such as mercury and cadmium are mined and used in manufacturing processes; some also occur as trace elements in fuels. They are released to the air as metal fumes or suspended particulates from fuel combustion, ore smelting, and incineration of wastes. Worldwide, a major source of lead in the atmosphere is the burning of gasoline containing tetraethyllead, which is added to gasoline to reduce knock and engine wear Approximately 2 million metric tons of lead are emitted to the atmosphere worldwide per year

ead and other volatile metals • Air in urban areas typically contains 5--l0 times as much lead as does air in rural areas in the many countries where leaded gasoline is used, and several times as much as in air found over other areas. Since leaded gasoline was phased out in the United States in the late 1970s, atmospheric lead concentrations in the United States have declined substantially .

zardous air pollutants (HAP • They are another class of air contaminants. A HAP is defined in the Clean Air Act as "an air Pollutant to which no ambient air quality standard is applicable and which causes or contributes to an increase in mortality or an increase in serious irreversible, or incapacitating reversible illness" Currently there are nearly 200 chemicals regulated as HAPs.

Carbon dioxide (CO2) • It is another compound of concern in the atmosphere. It is usually considered nontoxic and innocuous, and it is not generally listed as an air pollutant. However in the upper atmosphere, increasing concentrations of carbon dioxide have been implicated in global warming. This will be discussed in more detail later.