As mentioned earlier, depending on the fuels used, pollutants generated from power plants can include: sulfur dioxide (SO2), nitrogen oxides (NOX), mercury (Hg), particulate matter (including PM10 and PM2.5) and greenhouse gases such as methane (CH4), nitrous oxide (N2O) and carbon dioxide (CO2). Other compounds such as volatile organic compounds (VOCs) and trace metals are also emitted as air pollutants.
In order to provide an idea of the order of magnitude of the amount of pollutants emitted during the generation of electricity, Table 3.2 shows average emission rates of CO2, SO2 and NOX from electricity generation units using different fossil fuels.
Particulate emission rates vary widely, particularly for oil and coal, depending strongly on the amount of ash produced after burning. In the following sections brief descriptions of the pollutants covered in this report are given.
| Pollutant | Emission rates (kg/MWh) | ||
| Coal | Oil | Gas | |
| CO2 | 1,021.04 | 759.09 | 515.29 |
| SO2 | 5.90 | 5.45 | 0.05 |
| NOX | 2.72 | 1.82 | 0.77 |
Table 3.2. Typical Emission Rates from Different Fuels
Most air pollutants are generated during combustion, regardless of which type of fuel is burned. However, the amount and characteristics of each pollutant strongly depend on the fuel.
For instance, particulate matter generated from coal combustion results in particles of larger size, and containing greater amounts of organic and elemental carbon, than particulate matter generated from fuel oils.
Some metallic elements that are toxic pollutants, such as lead and mercury, are emitted from coal combustion, while oil combustion results in emissions of vanadium as well as lead, but almost no mercury.
Natural gas is the cleanest of all the fossil fuels, resulting mainly in emissions of NOX, CO2 and very small amounts of other pollutants.
Table 3.3 below shows the main health and environmental effects of some of the pollutants emitted by power plants.
|
NITROGEN OXIDES |
SULFUR DIOXIDE |
MERCURY |
CARBON DIOXIDE |
|
Component in ground-level ozone and smog |
Major precursor of fine particulate soot |
Humans are affected primarily by eatingcontaminated fish |
Contributes to global warming and climate change |
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Contributes to death, serious respiratory illnessand aggravates existing cardiovascular disease |
Disruption of the nervous system, damage to brainfunctions, DNA and chromosomal damage, allergic reactions, negativereproductive effects |
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|
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Reacts to acidify surface water, killing fish andother biota, including trees and soil organisms |
Mercury ingestion in animals can damage kidneys,intestines, DNA alteration |
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|
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Speeds weathering of monuments, buildings, metalstructures |
Loons, eagles, otters, mink, kingfishers andospreys are fish-eaters and are seriously affected by mercury exposurethrough the food web |
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Contributes to visual impairment (regional haze) |
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Table 3.3. Principal Health and Environmental Effects of the Main Pollutants Emitted by Power Plants
The main sources of sulfur compounds in air are anthropogenic, with sulfur dioxide (SO2) the predominant form.
Mercury is a known persistent, bioaccumulative and toxic (PBT) trace metal that occurs naturally in coal at very low concentrations. The combustion of coal is considered the major anthropogenic source of this pollutant to the atmosphere.
Particulate matter (PM) consists of a wide range of materials in solid or liquid phase that range in size from less than 1 nanometer up to one hundred micrometers and can have complex chemical composition.
Greenhouse gases (GHGs) are those gases that trap heat in the atmosphere; this allows an average temperature on Earth of approximately 15°C. Without this natural "greenhouse effect," the average ambient temperature would be about 33°C lower than it is now, making most life as we know it today impossible.
The most important anthropogenic sources of nitrogen oxides are combustion processes. Nitrogen oxides can be formed in combustion processes from the nitrogen contained in the fuel or from the nitrogen that is part of the air.
