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Omowumi Alabi Department of Geosciences

University of Missouri-Kansas City Kansas City, MO

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Atmospheric Atmospheric CompositionComposition

The primary components of air are nitrogen (N2), oxygen (O2) and water vapor (H2O). About 99 percent of dry air is nitrogen (78%) and oxygen (21%). The remaining percent includes trace quantities of substances such as carbon dioxide (CO2), methane (CH4), hydrogen (H2), argon (Ar) and helium (He).

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What is an Air Pollutant?A substance that is

- not naturally found in the air

- wrongly located or

- in high enough concentrations

such that it produces a detrimental environmental effect.

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Detrimental Environmental Detrimental Environmental EffectsEffects

The two basic physical forms of air pollution areThe two basic physical forms of air pollution are• Gases Gases • Particulate Matter Particulate Matter

These can affect These can affect -the health of humans -the health of humans (primarily the respiratory (primarily the respiratory system) system)

-the health of plants and animals -the health of plants and animals

-non-living materials-non-living materials

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Types of PollutantsTypes of Pollutants

Pollutants can also be classified as either primary pollutants or Pollutants can also be classified as either primary pollutants or secondary pollutants. secondary pollutants.

A A primary pollutantprimary pollutant is one that is emitted into the atmosphere is one that is emitted into the atmosphere directly from the source of the pollutant and retains the same directly from the source of the pollutant and retains the same chemical form i.e. the ash produced by the burning of solid waste.chemical form i.e. the ash produced by the burning of solid waste.The effect of primary pollutants is most pronounced in the The effect of primary pollutants is most pronounced in the immediate vicinity of the source. immediate vicinity of the source.

A A secondary pollutantsecondary pollutant is one that is formed by atmospheric is one that is formed by atmospheric reactions of precursor or primary emissions. reactions of precursor or primary emissions. Secondary pollutants are not emitted. Rather, they form in the air Secondary pollutants are not emitted. Rather, they form in the air when primary pollutants react or interact. An important example of when primary pollutants react or interact. An important example of a secondary pollutant is ozone. a secondary pollutant is ozone. Secondary pollutants take time to form and may not affect Secondary pollutants take time to form and may not affect the immediate vicinity of the pollutant source.the immediate vicinity of the pollutant source.

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Sources of Air Sources of Air PollutantsPollutants

A source of air pollution is any activity that causes pollutants to be emitted into the air.

Human-generated sources of air pollution are categorized in two ways: mobile and stationary sources.

Mobile sources of air pollution include most forms of transportation such as automobiles, trucks, and airplanes.

Stationary sources of air pollution consist of non-moving sources such as power plants and industrial facilities

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Types & Sources of Air Pollutants

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Stationary Stationary

SourcesSources Air pollution from stationary sources is produced by two primary activities:

- stationary combustion of fuel such as coal and oil at power generating facilities

-the pollutant losses from industrial processes such as refineries and chemical manufacturing facilities.

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Transport & Dispersion of Air Transport & Dispersion of Air PollutantsPollutants

On the local level, the primary On the local level, the primary factors affecting transport factors affecting transport and dispersion of pollutants and dispersion of pollutants are are windwind and and atmospheric atmospheric stabilitystability. .

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WindWind

• the natural horizontal motion of the natural horizontal motion of the atmospherethe atmosphere

• caused by differences in pressure caused by differences in pressure in the atmosphere. in the atmosphere.

• air moves from high pressure air moves from high pressure areas to low pressure areas areas to low pressure areas

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Effect of Wind on Dispersion of Effect of Wind on Dispersion of PollutantPollutant

• Wind speed can greatly affect the Wind speed can greatly affect the pollutant concentration in a local pollutant concentration in a local area.area.

• The higher the wind speed, the The higher the wind speed, the lower the pollutant concentration. lower the pollutant concentration.

• Wind dilutes pollutants and rapidly Wind dilutes pollutants and rapidly disperses them throughout the disperses them throughout the immediate area. immediate area.

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Atmospheric Atmospheric StabilityStability• refers to the vertical motion of refers to the vertical motion of

the atmosphere the atmosphere • UnstableUnstable atmospheric conditions atmospheric conditions

result in a vertical mixing, result in a vertical mixing, thereby promoting dispersal of thereby promoting dispersal of polluted air polluted air

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Typically, the air near the surface of the earth is warmer in the day time because of the absorption of the sun's energy. The warmer and lighter air from the surface then rises and mixes with the cooler and heavier air in the upper atmosphere causing unstable conditions in the atmosphere. This constant turnover also results in dispersal of polluted air.

Unstable Atmosphere Promotes Dispersal of Polluted Air

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Stable atmospheric conditions usually occur when warm air is above cool air and the mixing depth is significantly restricted. This condition is called temperature (or thermal) inversion. An inversion can prevent the rise and dispersal of pollutants from the lower layers of the atmosphere and cause localized air pollution problem.

Stable Atmospheric Condition Discourages Dispersal of Polluted Air

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Unstable Atmosphere•Temperature decreases with height

•Vertical air motion is promoted

•Horizontal air motion is promoted

•Promotes dispersion

Stable Atmosphere•Temperature increases with height•Vertical air motion is restricted•Horizontal air motion is restricted•Discourages dispersion