Air pollutants and Environmental Effects
Air pollution has the potential to seriously injure/cause:
Vegetation - Pollutants may visibly injure vegetation by bleaching, other colour changes, and necrosis, or by more subtle changes such as alterations in reproduction or growth. Table 1 summarizes some of the more common visual effects of air pollutants on vegetation. Air pollution can also result in measurable effects on forest ecosystems, such as reduction in forest growth, increased susceptibility to forest pests, and change in forest species. High-dose exposure to pollutants, which is associated with point source emissions such as smelters, often results in complete destruction of shrubs and trees in the surrounding area.
Table 1 - Examples of air pollution injury to vegetation.
| Pollutant | Symptoms |
|
Hydrogen fluoride Nitrogen dioxide Ozone |
Tip and margin burns, dwarfing White or brown collapsed lesion near leaf margins Flecking, stippling, bleached spotting |
| Peroxyacetylnitrate (PAN) | Glazing, silvering, or bronzing on lower leaf surfaces |
| Sulphur dioxide | Bleached spots, interveinal bleaching |
Data derived from Hodgson (2010).
A good example of air pollution effects on vegetation is the change in the forest vegetation of the San Bernadino Mountains in southern California. There, prolonged exposure to photochemical oxidants (smog) resulted in a shift from ozone-sensitive pine trees to more ozone-tolerant oaks and shrubs. Ozone injury in pines results in decreased photosynthesis due to foliar injury and premature needle fall, reduced nutrient retention in needles, and decreased growth. Generally, gaseous pollutants have the potential to disrupt plant-leaf biochemical processes through absorption by stomata or cuticle, while trace metals and organochlorine compounds tend to accumulate in organic matter and humus.
Animals - are affected either by uptake through the food chain or direct exposure via inhalation. Therefore, domestic animals can be affected directly by air pollutants. However, the main concern is chronic poisoning as a result of ingestion of forage that has been contaminated by airborne pollutants. Pollutants important in this connection are lead, arsenic, and molybdenum. Fluoride emissions from industries producing phosphate fertilizers and derivatives have damaged cattle throughout the world. The raw material, phosphate rock, can contain up to 4% fluoride, some of which is released into the air and water. Farm animals, particularly cattle, swine, and sheep are susceptible to fluoride toxicity (fluorosis) - characterized by mottled and soft teeth, and osterofluoritic bone lesions, which lead to lameness and, eventually, death.
Materials and Structures - Building materials have become blackened and soiled by smoke, and damage by chemical attack from acid gases in the air has led to the deterioration of many marble statues in western Europe. Metals are also affected by air pollution. For example, SO2 causes corrosion in many metals at a faster rate. Ozone is known to oxidize rubber products, and one of the effects of Los Angeles smog is cracking of rubber tires. Fabrics, paper, and leather are also affected by SO2 and sulphuric acid, causing them to crack, become brittle, and tear more easily.
Atmospheric Effects - The presence of fine particles (0.1-1.0 mm in diameter) or NO2 in the atmosphere can result in atmospheric haze or reduced visibility due to light scattering by the particles. The main effect of atmospheric haze has been degradation in visual air quality and this is of particular concern in areas of scenic beauty, including most of the major national parks (e.g. Grand Canyon, Great Smoky Mountain, Yosemite, Zion Parks).
There is also concern with the increase of CO2 in the atmosphere because this pollutant absorbs heat energy strongly and retards the cooling of the earth. This is frequently referred to as the greenhouse effect; theoretically, an increase in CO2 levels would result in a global increase in air temperatures. In addition to CO2, other gases contributing to the greenhouse effect include methane, nitrous oxide, CFCs, and ozone.
Certainly, the potential impact of global climate change on biodiversity is significant. The amount of production or the type of plant that will grow efficiently may change in response to increasing CO2, changes in the amount and timing of precipitation, or to the amount of available solar radiation. CO2 enrichment alone would increase the rate of plant growth, while higher temperatures would increase the rate of microbial decomposition of organic matter, adversely affecting soil fertility. On the other hand, higher temperatures usually hasten plant maturity in annual species, shortening the growth stages of some plants. At the same time, midlatitude summer dryness is likely to reduce yields by 10%-30%.
Therefore, global warming brings about climate changes that cause disturbance in agriculture and food production, changes in the livelihood of plants and animals, melting of snow caps and also increase in sea levels. Additional information on climate change, global warming and greenhouse effect can be found in the following link:
http://www.globalissues.org/article/233/climate-change-and-global-warming-introduction
Acidic Deposition - is the total combined of wet and dry deposition, with wet acidic deposition being commonly referred to as acid rain. As shown in figure 1, sulphur dioxide and oxides of nitrogen react with water vapour of the atmosphere and produce sulphuric acid and nitric acid (clouds). These acids then return to the earth´s surface with rainwater. In common language, acid rains means the presence of excessive acids in rainwater (fig. 1). Normal uncontaminated rain has a pH of about 5.6, but acid rain generally has a pH of less than 4.0. In the eastern United States, the acids in acid rain are approximately 65% sulphuric, 30% nitric, and 5% other; whereas in the western states, 80% of the acidity is due to nitric acid.
Source: Jinting (2011); http://jinting89.blogspot.pt/
Many species of freshwater animals have been affected by wet deposition of sulphur dioxides ("acid rain"). Many lakes in northeastern North America and Scandinavia have become so acidic that fish are no longer able to live there. The low pH not only directly affects fish, but also contributes to the release of potentially toxic metals (e.g. aluminium) from the soil. The maximum effect occurs when there is little buffering of the acid by soils or rock components. Maximum fish kills occur in early spring due to the "acid shock" from the melting of winter snows. Much of the acidity in rain may be neutralized by dissolving minerals in the soil, such as calcium, aluminum, sodium, magnesium, and potassium, which are leached from the soil into surface waters. The ability of the soil to neutralize or buffer the acid rain is extremely dependent on the alkalinity of the soil. For example, much of the area in eastern Canada and the northeastern United States is covered by thin soils with low acid neutralizing capacity. In such areas, lakes are more susceptible to the effects of acid deposition leading to a low pH and high levels of aluminum, a combination toxic to many species of fish. Thus, acid rain harms aquatic life by entering into ground and river waters and generally, fish are most sensitive to acidification followed by invertebrates, algae, and microbes.
A second area of concern is that of reduced tree growth in forests. The leaching of nutrients from the soil by acid deposition may cause a reduction in future growth rates or changes in the type of trees to those able to survive in the altered environment. In addition to the change in soil composition, there are the direct effects on the trees from nitrogen and sulphur oxides as well as ozone. Acid rain can cause damage to leaves.
The phenomenon of acid rain is also explained in the following links:
http://www.epa.gov/acidrain/index.html
http://epa.gov/acidrain/education/site_students/index.html
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