|
|
Air Pollution |
The sources of air pollutants can be classified in two major categories stationary sources and mobil sources. Air pollution major health effect is the result of irritants acting on the respiratory tract. Research indicates that the most serious health effects associated with polluted air can be attributed to elevated levels of very fine particulates (PM 2.5µm or less). Also, ozone and other photochemical oxidans plus nitrogen dioxide can cause major respiratory problems.
Also know as termal inversions or air inversion, they occur when a stable layer of warmer air overlays cooler air.
 |
In valleys or on the lee side of mountains, temperature inversion may occur. (See diagram above). A warmer air mass moves above cooler air, trapping the cooler, denser air underneath and increasing the severity of air pollution. The city of 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 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 (see above diagram) where warm air overlies the colder air which accumulates in the valleys.
 |
Also, cities tend to form features known as heat island or dust domes, which tend to collect warm air filled with pollutants, and help spread it out over nearby suburbs. (See diagram above). Temperatures in large cities are frequently 3° to 5°C higher than the surrounding countryside.
Long-range transport of air pollutants - indutrial pollutants and automobile emmissions are transported great distances by wind currents. This makes the control of air pollution more difficult since it may cross states and countries boundaries.
Human Health -
 |
| Plant Damage due
to air pollution specifically acid deposition |
Plant Pathology - Air pollution can cause direct toxic effect in the plants. It may cause chlorosis or bleaching of the chlorophyl, leading to necrosis or death. Also, it have been shown that air pollution may change or damage metabolic regulators or plant hormones altering the plant growth.
Acid Deposition - It is more commonly know as acid rain, but it includes not only rain but also snow, fog, dry SO2 and NO2 gas, and sulfate and nitrate aerosols.
Acid rains forms when ceratin atmospheric gases (primarily carbon dioxide, sulfur dioxide, and nitrogen oxides) come in contact with water in the atmosphere or on the ground and are chemically converted to acidic substances. Carbon dioxide dissolved in rain is converted to weak acid (carbonic acid). Other gases, primarily oxides of sulfur and nitrogen, are converted to strong acids such as sulfuric acid and nitric, nitrate acids.
 |
| A comparison between the pH of Acid Rain and other substances |
Humans activities, primarily air pollution can make the rain very acid. Occasional pH readings of well below 2.4 (the acidity of vinegar) have been reported in industrialized areas. Since the pH scale is logarithnic, rainfall with a pH of 4.0 is ten times more acid than precipitation with a pH of 5.0, and 100 times more acid than that of pH 6.0. So, acid deposition with a pH of 2.4 is 10,000 times more acid than unpolluted rainfall which have a pH of 5.0.
Acid deposition can cause a number of adverse effects to the environment. These include the following:
  |
| Marble exposed to acid rain |
Acid precipitation affects stone primarily in two ways: dissolution and alteration. When sulfuric and nitric acids in polluted air react with the calcite in marble and limestone, the calcite dissolves. This caused that sharp edges and carving details gradually become rounded.
Click here to go to the EPA web site on acid rain.
Click here to know more on how acid deposition affect marble and limestone buildings.
Air Quality Program of National Safety Council.
| Previous Lesson | Syllabus | HOME | Next Lesson | List of Lessons | List of Assignments |  |