Control of Air Pollution

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Control of Air Pollution

adapted to HTML from lecture notes of Prof. Stephen A. Nelson Tulane University

Control of Air Pollution Introduction
Air Inversion
Global Warming
Greenhouse Gases
Acid Rain
Ozone Depletion (.gif animation)

see also Acid Rain page...

Control of Air Pollution

Automobiles Catlytic converter
 - Converts carbon monoxide, nitrous oxides and hydrocarbons into carbon dioxide, nitrogen and water.
Recirculating exhaust gas along with a catlytic converter greatly reduces emissions.

Main problem is the sulfur dioxide it produces upon burning. Solutions: Burn only low sulfur coal.
Wash coal to remove pyrite.

Convert coal to gas (called Gasification)
Fluidized Bed Combustion (or Limestone Injection): Mix coal with limestone, to form calcium sulfides or sulfates, which are prevent sulfur from forming sulfur dioxide.
Scrubbing - slurries of lime or limestone.


Smoke plus Fog (U.K.) (Grey smog). Photochemical Smog - brown air. (U.S.A.)
Results from exhausts from cars, buses and trucks.

Nitrogen Oxide + Oxgen + Hydrocarbons + Sunlight -- > Ozone

6ppm ozone is deadly - We need ozone in stratosphere; at lower altitudes, however, it can kill.
Sulfurous Fog- gray air.Dominantly from burning coal with a significant pyrite content. The fogs of  London in the past were actually sulfuous fog. This type of smog is no longer common in London as a result of environmental regulations on burning coal.

Air Inversion

In valleys or on the lee side of mountains, air inversion may occur. A warmer air mass moves above cooler air, trapping the cooler, denser air underneath and increasing the severity of air pollution. Los Angeles is a good example of this, where warm desert air from the east comes over the mountains to the east of Los Angeles and lies over the cooler Pacific Ocean air. The cooler air is trapped because it cannot rise through the less dense warm air above it, and the pollution in the cold air accumulates.

A similar situation arises in mountain valleys where warm air overlies the colder air which accumulates in the valleys.


Also, cities tend to form featuers known as heat islands or dust domes, which tend to collect warm air filled with pollutants, and help spread it out over nearby suburbs.


Global Warming


If there were no greenhouse effect, the average temperature on the earth would be - 20C with huge fluctuations in a 24 hour period. When visible light from the sun hits the earth some is absorbed, heating the earth.   The heated earth gives off infrared radiation characteristic of the 25C temperature. This longer wavelength infrared radiation  is then reradiated back into space. Some of the  infrared radiation, however, is  trapped (absorbed) by greenhouse gases.
This is known as The Greenhouse Effect.

There are several gases which cause the greenhouse effect, and whose concentrations determine the amount of heat retained by the earth. Primary among these are water vapor, carbon-dioxide and methane. The chart below shows how the concentration of CO2 in the atmosphere has changed in the last 40 years:


The increase in CO2 is anthropogenic (related to human activities). It is mostly due to the burning of fossil fuels and deforestation.

Gases contributing to Anthropogenic Greenhouse Effect
Gas  Rate of Increase 
(% per year) 
Relative Contribution(%) 
CO2  0.5  60 
CH4  15 
N2O  0.2 
O3  0.5 

Global Warming has been studied extensively, and currently, a large percentage of the scientific community have reached a consensus on various issues related to global warming. They are listed below:

Scientific Consensus on Global Warming
Statement  Consensus 
Fundamental Physics  90+% 
Added greenhouse gases add heat  90+% 
Added gases are anthropogenic  90+% 
Reduction of uncertainty will require a decade  90+% 
Full recovery will require many centuries  90+% 
Large stratospheric cooling  90+% 
Precipitation will increase  90% 
Reduction of sea ice  90% 
Warming in arctic  90% 
Rise in sea level  90% 
Local details of global change 
Tropical storms increase 
Details of next 25 years 

Greenhouse Gases

Carbon Dioxide (CO2): Roughly 60% of total
Burning Fossil Fuels
Methane (CH4): 15% of total
Coal Mines

Acid Rain

Main source of acid rain is sulfur dioxide and nitrogen oxides in the atmosphere.
Power plants are a major source for sulfur dioxide and as well nitrogen oxide.
Automobiles, trucks and buses are major contributors of nitrogen oxides in urban and suburban environments.

Effects of Acid Rain

Ozone Depletion

animation ozone depletion


Acid Rain

Air Pollution

Global Warming