Coal-Fired Power Plants (CFPPs)
How does NOx impact our environment and health?
There are a number of health and environmental issues attributed to NOx and derivatives in the family
of nitrogen oxides, including smog, acid rain, and possibly global warming. The NOx family includes
various compounds including nitrogen dioxide, nitric acid, nitrous oxide, nitrates, and nitric oxide.
NOx and associated pollutants can be transported
over great distances by the prevailing winds in the U.S. and the world.
NOx can react with other compounds and form nitrate particulate, acid aerosols, and toxic chemicals.
A major health concern of these pollutants is the damage they can cause to the human respiratory system.
If small particulates penetrate sensitive parts of the lungs, they can damage the tissue and
consequentially cause or worsen respiratory diseases, such as emphysema and bronchitis.
|| This diagram shows how anthropogenic (human caused) sources of emissions flow into the atmosphere and combine to form acid rain, which then returns to earth.
Ground-level ozone, or smog, forms when volatile organic compounds (VOCs - organic chemicals
containing carbon, oxygen, hydrogen, chlorine, and other atoms) and NOx react in sunlight. Smog can have
adverse effects on people with lung disease or can cause damage to the lungs of anyone who has long-term
exposure. Smog, like many pollutants, can be carried great distances on the earth’s air currents.
Acid rain occurs when NOx and sulfur dioxide (SO2), another emission, react with other
substances to form acids. These acids form in the air and travel on air currents before falling to the
earth captured in rain, fog, snow, and even dry particulate. In addition to the damage caused to physical
structures, acid rain can cause lakes and streams to become acidic.
One member of the NOx family, nitrous oxide, is reported to be a greenhouse gas. You have, no doubt,
heard of the “greenhouse effect” in the news. So, what is the greenhouse gas effect? Well, here is how
Energy from the sun (solar radiation) travels to the earth where some of the energy is reflected back
into space by the earth’s atmosphere, but most passes through the atmosphere and warms the earth’s
surface (water, land, etc.). However, if it weren’t for the earth's atmosphere trapping the energy, the
earth's surface would still be cold. Some of the absorbed energy radiates back from the surface to warm
the earth’s lower atmosphere. Half of the energy absorbed by the earth’s surface evaporates water –
causing a vapor. When this water vapor condenses in the atmosphere, we get rain and snow. Only a small
amount of heat radiated back from the earth’s surface escapes out to space. Most of the heat captured
by the atmosphere is attributed to greenhouse gases, hence the term “greenhouse effect.” While it is
true that the amount of greenhouse gas in the atmosphere fluctuates and also true that manmade causes
contribute a small amount of greenhouse gas, man could not exist on the earth if it wasn’t for the
atmosphere containing greenhouse gasses.
Greenhouse gases accumulate in the atmosphere and possibly cause a rise in the earth's temperature.
It is difficult to ascertain that any one gas attributes more to the greenhouse effect than another. But
it is useful to note that the list of greenhouse gases is long and includes carbon dioxide, sulfur
hexaflouride, hydroflourocarbons, perfluorocarbons, chlorofluorocarbons … and water vapor. That’s right,
water vapor is a natural greenhouse gas that could contribute as much as 70% of the greenhouse effect
on the earth, and that does not include clouds.
The image to the upper-right shows water vapor surrounding the earth from a Geostationary Operational
Environmental Satellite (GOES). This image shows the distribution of water vapor that surrounds the
planet, relative to the oceans, clouds, and continents of the Earth. Note that the vapor is unevenly
Keep in mind, trapped heat within our atmosphere is a critical part of the earth’s climate. Under ideal,
balanced conditions, the amount of energy entering the system from solar radiation will exactly match
the amount of energy being radiated into space. In this scenario, the earth would maintain a constant
climate. However, because no system is ever perfectly balanced, we can assume that the earth will
periodically experience fluctuations in the amount of retained heat and the amount of greenhouse gases
in the atmosphere. These fluctuations would include periods of global warming and global cooling. Now
add a human element generating additional greenhouse gases and you can understand the concern
surrounding the issue.