Environmental Engineering Reference
In-Depth Information
ozone or photochemical ozone, is a secondary pollutant formed when VOCs react with
nitrogen oxides in the presence of sunlight (EPA, 2003).
High levels of stratospheric ozone affect plant growth, deteriorate electronic equipment,
fade dyes and paints, and cause respiratory ailments. Crops that grow in high levels of ozone
areas significantly decline in yield with the subsequent impact to the economy (EPA, 2003).
In the case of humans, even low levels of ozone react with molecules in the airway lining,
causing acute inflammation and respiratory illnesses, including loss of protection against
microorganisms (Allen, 2002).
Emissions with global impact
Greenhouse gases
Solar radiation coming as visible light is partially reflected and partially transmitted by
the Earth's atmosphere. The transmitted fraction reaches the Earth and produces a warming
effect on the surface. The Earth's surface then emits part of the absorbed energy as infrared
radiation back to the atmosphere where it is partially intercepted, absorbed, and re-emitted
in all directions by “greenhouse gas molecules.” Succinctly, this is the principle called
“greenhouse effect” that keeps the planet warm enough to be inhabitable.
Although oxygen and nitrogen are the main components of the Earth's atmosphere, they
are both transparent to infrared radiation. Other molecules, however, such water vapor, carbon
dioxide, methane, nitrous oxide, and ozone are naturally occurring GHGs. In addition to these
compounds, several man-made gases containing fluorine, chlorine, or bromine are greenhouse
gases as well.
Scientific evidence shows that the temperature of the atmosphere has increased in the last
100 years by around 0.5°C. Many atmospheric scientists firmly believe that this is happening
as a consequence of human activity, which is raising the concentration of GHGs in the
atmosphere.
From preindustrial times to 2006, carbon dioxide has increased from 278 to 380ppm,
methane rose from 0.715 to 1.774 ppm, and nitrous oxide increased from 0.270 to 0.319 ppm
(Intergovernmental Panel on Climate Change [IPCC], 2007).
From the energy point of view, carbon dioxide is the most degraded form of carbon
that is the result of chemical and biological processes of combustion, respiration, and
decay of plant and animal matter. Autotrophic organisms, such as green plants and
phytoplankton, are able to use carbon dioxide as a substrate to produce sugars via
photosynthesis and thus closing the carbon cycle. By absorbing carbon dioxide, oceans
are sinks of inorganic carbon, which after its transformation into calcium carbonate it
precipitates to the ocean floor. However, the level of carbon dioxide production as a result
of fossil fuel combustion, cement production, and deforestation has overwhelmed plants
and oceans capabilities of carbon dioxide sequestration. From 1751 to 2010, approximately
337 billion tons of carbon dioxide has been released to the atmosphere from the
consumption of fossil fuels, cement production, and gas flaring (Boden et al., 2010). As
an outcome, the level of carbon dioxide in the atmosphere has been increasing steadily as
can be seen in Figure 8.2.
Methane is produced by anthropogenic and natural processes. Main anthropogenic sources
include anaerobic processes that decompose organic matter, such as in wetland rice cultivation,
enteric fermentation, composting, wastewater treatment, combustion of biomass, and fossil
fuel production, such as coal, natural gas, and oil (“Methane: Sources and emissions,” n.d.).
Natural sources are wetlands, gas hydrates, permafrost, termites, oceans, freshwater bodies,
