Air Pollution
I. A Brief History of Air Pollution
a. The atmosphere is one of the most convenient places to dispose unwanted materials because it is the fastest moving fluid
medium in the environment.
b. Since we used fire, the atmosphere became a sink for waste disposal.
II. Stationary and Mobile Sources of Air Pollution
a. Stationary Sources
i. Relatively fixed location
1. Point sources: emit pollutants from one or more controllable sites
2. Fugitive sources: generate air pollutants from open areas exposed to wind processes. (burning for agricultural purposes)
3. Area sources: well-defined areas within which are several sources of air pollutants. (small urban communities)
b. Mobile Sources
i. Move from place to place while emitting pollutants.
1. Automobiles, trucks, aircrafts, trains, ships, etc.
III. General Effects of Air Pollution
a. Affects many aspect of environment
i. Visual qualities, vegetation, animals, soils, water quality, human health, etc.
b. Many air pollutants have synergistic effects
i. The combined effects are greater than the sum of the separate effects.
IV. Air Pollutants
a. Primary and Secondary Pollutants, Natural and Human
i. Primary Pollutants: Emitted directly into the air (sulfur dioxide, carbon monoxide, nitrogen oxides, hydrocarbons)
ii. Secondary Pollutants: produced through reactions between primary pollutants and normal atmospheric compounds (ozone
forms over urban areas through reactions of primary pollutants, sunlight, and natural atmospheric gases.)
iii. Natural Pollutants
1. Sulfur dioxide from volcanic eruptions
2. Hydrogen sulfide from geysers and hot springs and bog and marshes
3. Ozone in the lower atmosphere because of unstable meteorological conditions (violent thunderstorm)
4. Emission of variety of particles from wildfires and windstorms.
5. Natural hydrocarbon seeps
b. Criteria Pollutants
i. Six criteria
1. Sulfur dioxide: colorless and odorless gas at Earth’s surface in low concentrations
2. Nitrogen Oxides: yellow-brown to reddish-brown gas. Occur in many forms in the atmosphere
3. Carbon Monoxide: colorless, odorless gas; very toxic even in low concentrations. 90% comes from natural sources.
4. Ozone and Other Photochemical Oxidants: resulted from atmospheric interactions of nitrogen dioxide and sunlight.
5. Particulate Matter (PM 10 and PM 2.5) and Ultrafine Particles: varying mixtures of particles suspended in the air we breathe.
Asbestos is dangerous.
6. Ultrafine Particles: cannot be easily filtered and are so small that they can enter the bloodstream. Evidently can contribute to
inflammation.
7. Lead: it is emitted into the air with the exhaust because it is in gasoline.
c. Air Toxics
i. Those pollutants that are known or suspected to cause cancer or other serious health problems.
1. Hydrogen Sulfide: highly toxic corrosive gas; rotten egg odor. (geysers, swamps, bogs, industrial plants)
2. Hydrogen Fluoride: gaseous pollutant released by some industrial activities such as production of aluminum, coal gasification,
and burning of coal in power plants.
3. Methyl Isocyanate: so toxic that extreme care must be taken to ensure they don’t enter the environment.
4. Volatile Organic Compounds: variety of organic compounds used as solvents in industrial processes such as dry cleaning,
degreasing, and graphic arts.
5. Benzene: additive in gasoline and is an important industrial solvent.
6. Arcolein: volatile hydrocarbon that that is extremely irritating to the nose eyes and respiratory system in general.
V. Variability of Air Pollution
a. Haze from Afar: not restricted to urban areas
VI. Urban Air Pollution
a. Influences of Meteorology and Topography: Meteorological conditions can determine whether air pollution is a nuisance or a
major health problem.
i. Atmospheric Inversion: warmer air is found above cooler air and it poses a particular problem when there is a stagnant air mass.
b. Potential for Urban Air Pollution
i. Rate of emission of pollutants per unit area
ii. Downwind distance that a mass of air moves through an urban area
iii. Average speed of the wind
iv. Elevation to which potential pollutants can be thoroughly mixed by naturally moving air in the lower atmosphere.
c. Smog: mixture of smoke and fog that produced unhealthy urban air.
i. Photochemical smog (L.A. type smog or brown air)\
ii. Sulfurous smog (London-type smog, gray air, or industrial smog)
d. Future Trends for Urban Areas: developed countries with burgeoning populations are particularly susceptible to air pollution
now and will be in the future.
VII. Pollution Control
a. Pollution Control: Particulates
i. Emitted from fugitive, point, or area stationary sources are much easier to control than are the very small particulates of primary
or secondary origin released from mobile sources, such as automobiles.
b. Pollution Control: Automobiles
i. Most common device to reduce carbon monoxide and hydrocarbon emissions from automobiles is the exhaust system’s catalytic
converter.
c. Pollution Control: Sulfur Dioxide
i. Can be reduced through abatement measures performed before, during, or after combustion.
ii. Coal gasification: converts coal that’s relatively high in sulfur to a gas in order to remove the sulfur.
iii. Scrubbing: technology to scrub sulfur dioxide and other pollutants at power plants was developed in the 1970s.
VIII. Air Pollution Legislation and Standards
a. Clean Air Act Amendments of 1990
i. Comprehensive regulations enacted by the U.S. Congress that address acid rain, toxic emission, ozone depletion, and
automobile exhaust.
b. Ambient Air Quality Standards
i. Tied to emission standards that attempt to control air pollution.
ii. Air Quality Index: used to describe air pollution on a given day.
IX. Cost of Air Pollution Control
a. The cost of air pollution control varies tremendously from one industry to another.
X. Ozone Depletion
a. Ozone: Triatomic form of oxygen in which three atoms of oxygen are bonded.
b. Ultraviolet Radiation and Ozone
i. Ozone Shield: absorbs most of the potentially hazardous ultraviolet radiation that enters Earth’s atmosphere from the sun.
ii. Ultraviolet C (UVC) has the shortest wavelength and is the most energetic of the types of ultraviolet radiation.
iii. Ultraviolet A (UVA) radiation has the longest wavelength and the least energy of the three types of ultraviolet radiation.
iv. Ultraviolet B (UVB) radiation is energetic and is strongly absorbed by stratospheric ozone.
c. Measurement of Stratospheric Ozone
i. Dobson unit (DU) is commonly used to measure the concentration of ozone
XI. Ozone Depletion and CFCs
a. Chlorofluorocarbons (CFCs)
b. Emissions and uses of ozone-depleting chemicals
i. Emissions of chemicals thought to destroy stratospheric ozone.
ii. Simplified stratospheric chlorine chemistry
1. CFCs are considered responsible for most of the ozone depletion observed by scientists.
c. The Antarctic ozone hole
d. Polar Stratospheric Clouds
i. Have been observed for at least the past hundred years at altitudes of approximately 20 km above the Polar Regions.
e. An Arctic Ozone Hole?
f. Tropical and Midlatitude Ozone Depletion
g. The Future of Ozone Depletion
h. Environmental Effects
i. Ultraviolet (UV) Index: developed by the National Weather Service and the Environmental Protection Agency.
i. Management Issues
i. The Montreal Protocol: A diplomatic achievement of monumental proportions was completed with the signing of the Montreal
Protocol in September 1987.
ii. Substitutes for CFCs
iii. Hydrofluorocarbons (HFCs)
iv. Hydrochlorofluorocarbons (HCFCs)
v. These chemicals are controversial and more expensive than CFCs but do have advantages.
vi. Short-term adaptation to ozone depletion