لخّصلي

The conversion of energy from one form to another
often affects the environment and the air we breath
in many ways. Thus, study of energy is not
complete without considering its impact on the
environment (Fig. 2.62). Fossil fuels (e.g., coal, oil,
and natural gas) have been powering the industrial
development and the amenities of modern life since
the 1700s, but this has undesirable side effects.
The environment (i.e., the soil, water, and air) has
been paying a heavy toll for it.
Pollutants emitted during the combustion of fossil
fuels are responsible for smog, acid rain, global
warming, and climate change. The environmental
pollution has reached such high levels that it has
become a serious threat to vegetation, wildlife, and
human health.
Air pollution has been the cause of numerous
health problems, including asthma and cancer.
Many people die each year due to heart and lung
diseases related to air pollution
Hundreds of elements and compounds (e.g.,
benzene and formaldehyde are emitted during the
combustion of coal, oil, natural gas, and wood in
electric power plants, vehicles engines, furnaces,
and even fireplaces). Some compounds are added
to liquid fuels for various reasons (e.g., Methyl
tertiary-butyl ether (MTBE) is added to raise the
octane number of the fuel and to oxygenate the
fuel in winter months to reduce urban smog). The
largest source of air pollution is motor vehicles
The pollutants released by vehicles are usually grouped as
hydrocarbons (HC), nitrogen oxides (NOx), and carbon
monoxide (CO). HC emissions make up the large portion of
volatile organic compound (VOC) emissions. A significant
portion of the VOC or HC emissions is caused by the
evaporation of fuels during refuelling or spillage during spit
back or evaporation from gas tanks with faulty caps that do
not close tightly
Ozone and Smog
Smog is the dark yellow or brown haze that builds up in a
large, stagnant air mass and hangs over the populated areas
on calm, hot summer days. Smog is made-up mostly of
ground-level ozone O3
, but also contains numerous other
chemicals including carbon monoxide CO, particulate matter
such as soot and dust, volatile organic compounds VOCs
such as benzene, butane, and other hydrocarbons
Unlike the useful ozone layer high in the
stratosphere that protects the earth from the sun’s
harmful ultraviolet rays, ozone at ground level is a
pollutant with several adverse health effects.
The primary source of both nitrogen oxides and
hydrocarbons is motor vehicles. Hydrocarbons and
nitrogen oxides react in the presence of sunlight on
hot, calm days to form ground-level ozone,
Smog formation usually peaks in late afternoons
when the temperatures are highest and there is
plenty of sunlight. Ground-level smog and ozone form
in urban areas with heavy traffic or industry, but the
prevailing winds can transport them several hundred
miles to other cities (i.e., pollution knows no
boundaries, it is a global problem)
Ozone irritates eyes and damages the air sacs in the lungs
where oxygen and carbon dioxide are exchanged, causing
eventual hardening of this soft and spongy tissue. It also
causes shortness of breath, wheezing, fatigue, headaches,
and nausea, and aggravates respiratory problems such as
asthma. Staying indoors and minimizing physical activity
during heavy smog minimizes damage.
Ozone also harms vegetation by damaging leaf tissues.
Reformulated gasoline (RFG) that contains at least 2 percent
oxygen was introduced to improve the air quality in areas with
the worst ozone problems. The use of RFG has resulted in a
significant reduction in the emission of ozone and other
pollutants, and its use is mandatory in many smog-prone areas.
The other serious pollutant in smog is carbon monoxide; a
colourless, odourless, and poisonous gas.
CO is mostly emitted by motor vehicles and can build to
dangerous levels in areas with heavy congested traffic. It
deprives the body’s organs from getting enough oxygen by
binding with the red blood cells. At low levels, CO decreases
the amount of oxygen supplied to the brain and other organs
and muscles, slows body reactions, and reflexes, and impairs
judgment. It poses a serious threat to people with heart
disease and to fetuses. At high levels, CO can be fatal fatal,
as evidenced by the many deaths by cars warmed up in
closed garages or exhaust gases leaking into the cars.
Smog also contains suspended particulate matter (e.g., dust
and soot emitted by vehicles and industrial facilities), which
irritate the eyes and the lungs since they may carry acids and
metals compounds such as acids and metals
Acid Rain
Fossil fuels are mixtures of various chemicals, including
small amounts of sulfur. The sulphur in the fuel reacts with
oxygen to form sulfur dioxide (SO2
), which is an air pollutant.
The main source of SO2
is the electric power plants that
burn high-sulfur coal. The Clean Air Act of 1970 has limited
the SO2 emissions severely by forcing the plants to install
SO2 scrubbers, to switch to low-sulphur coal, or to gasify the
coal and recover the sulphur.
The Clean Air Act of 1970 has limited the SO2 emissions
severely by forcing the plants to install SO2 scrubbers, to
switch to low-sulphur coal, or to gasify the coal and recover
the sulphur. Motor vehicles also contribute to SO2
emissions since gasoline and diesel fuel also contain small
amounts of sulphur. Volcanic eruptions and hot springs also
release sulphur oxides (the cause of the rotten egg smell)
The sulphur oxides and nitric oxides react with
water vapour and other chemicals high in the
atmosphere in the presence of sunlight to form
sulfuric and nitric acids (Fig. 2.65). The acids
formed usually dissolve in the suspended water
droplets in clouds or fog and washed from the air
on to the soil by rain or snow. This process is
known acid rain.
Soil can neutralize a certain amount of acid, but
the amounts produced by burning high-sulphur
coal are more than the soil can handle. As a
result, many lakes, and rivers in industrial areas
have become too acidic for fish to grow. Forests in
those areas also experience a slow death
because they absorb the acids through their
leaves, needles, and roots. Even marble
structures deteriorate due to acid rain.
The Greenhouse Effect: Global Warming and Climate
Change
Glass at thicknesses encountered in practice transmits over
90 percent of radiation in the visible range and is practically
opaque (non-transparent) to radiation in the longer
wavelength infrared regions (i.e., allows the solar radiation to
enter freely but blocks the infrared radiation emitted by the
interior surfaces). This causes a rise in the interior
temperature of a car left under direct sunlight on a sunny day
because of the thermal energy buildup in the interior of the
car. This heating effect is known as the greenhouse effect
because it is exploited primarily in greenhouses.
The greenhouse effect is also experienced on a larger scale on
earth. The surface of the earth, which warms up during the day
as it absorbs solar energy, cools down at night by radiating part
of its energy into deep space as infrared radiation
Carbon dioxide (CO2
), water vapour, and trace
amounts of some other gases (e.g., methane
and nitrogen oxides) act like a blanket and
keep the earth warm at night by blocking the
heat radiated from the earth, Fig. 2.66). These
gases are called greenhouse gases with CO2
being the primary component.
Water vapour is usually taken out of this list
since it comes down as rain or snow as part of
the water cycle and because human activities
that produce water (e.g., the burning of fossil
fuels) do not have much impact on its
concentration in the atmosphere, which is
mostly due to evaporation from rivers, lakes,
and oceans.
However, CO2
is different because people’s activities do make
a difference in CO2 concentration in the atmosphere.
The greenhouse effect makes life on earth possible by keeping
the earth warm. However, excessive amounts of these gases
disturb the delicate balance by trapping too much energy, which
causes the average temperature of the earth to rise and the
climate at some localities to change. These undesirable
consequences of the greenhouse effect are referred to as
global warming or global climate change.
Global climate change is due to the excessive use of fossil fuels
(e.g., coal, petroleum products, and natural gas in electric power
generation, transportation, buildings, and manufacturing), and it
has been a concern in recent decades. In 2016, a total of 9.9
billion tons of carbon was released to the atmosphere as CO2
In 2018, the concentration of CO2
in the atmosphere was
about 400 ppm (i.e., 0.04 percent), which is 30 percent higher
than the level a century ago, and it is projected to increase to
over 700 ppm by the year 2100. Under normal conditions,
vegetation consumes CO2 and releases O2 during
photosynthesis, thus keeps the CO2 concentration in the
atmosphere in check. A mature, growing tree consumes about
12 kg of CO2 a year and exhales enough oxygen to support a
family of four. However, deforestation and the huge increase in
CO2 production in recent decades has disturbed this balance.
In a 1995 report, the earth world’s leading climate scientists
concluded that the earth has already warmed about 0.5°C
during the last century, and they estimate that the earth’s
temperature will rise another 2°C by the year 2100.
A rise of this magnitude can cause severe changes in weather
patterns with storms and heavy rains and flooding at some parts
and drought in others, major floods due to the melting of ice at
the poles, loss of wetlands and coastal areas due to rising sea
levels, variations in water supply, changes in the ecosystem due
to the inability of some animal and plant species to adjust to the
changes, increases in epidemic diseases due to the warmer
temperatures, and adverse side effects on human health and
socioeconomic conditions in some areas.
The seriousness of these threats has moved the United Nations
to establish a committee on climate change. A world summit in
1992 in Rio de Janeiro, Brazil, attracted world attention to the
problem. 162 nations signed an agreement prepared by the
committee in 1992 to control greenhouse gas emissions.
In the 1997 meeting in Kyoto (Japan), the world’s
industrialized countries adopted the Kyoto Protocol and
committed to reduce their CO2 and other greenhouse gas
emissions by 5 percent below the 1990 levels by 2008 to
2012. In December 2011, countries agreed in Durban, South
Africa, to forge a new deal forcing the biggest polluting
countries to limit greenhouse gas emissions. The Kyoto
Protocol was extended to allow five more years to finalize a
wider agreement. The goal was complete producing a new,
legally binding accord to cut greenhouse gas emissions by
2015 that would come into force by 2020.
In 2015, the United Nations Climate Change Conference held
in Paris (France), resulted in the Paris Agreement on the
reduction of climate change. The conference included
participants from 196 nations.
The main result of the conference was the establishment of a
goal to limit global warming to less than 2°C compared to
preindustrial times. According to the agreement, human-made
greenhouse emissions should be eliminated during the second
half of the 21st century.
Greenhouse gas emissions can be reduced by increasing
conservation efforts, improving conversion efficiencies, and meet
new energy demands by using renewable energy (e.g.,
hydroelectric, solar, wind, and geothermal energy) rather than
fossil fuels.
Major sources of greenhouse gas emissions are the industrial
sector and transportation. Each kilowatt-hour of electricity
produced by a fossil-fuelled power plant produces 0.6 to 1.0 kg
of carbon dioxide. Each liter of gasoline burned by a vehicle
produces about 2.5 kg of CO2
An average car driven about 13,500 miles a year and
consumes about 600 US gallons (1680 kg; 1 US gallon is
3.78541178 litres while an imperial gallon is 4.546092 litres)
of gasoline emits about 12,000 lbm of CO2
to the atmosphere
a year, which is about four times the weight of a typical car.
This and other emissions can be reduced significantly by
buying an energy-efficient car that burns less fuel over the
same distance, and by driving sensibly.
Saving fuel also saves money and the environment (e.g.,
choosing a vehicle that gets 30 rather than 20 miles per
gallon will prevent 2 tons of CO2
from being released to the
atmosphere every year while reducing the fuel cost by $1000
per year under average driving conditions of 13,500 miles a
year and at a fuel cost of $4.4/gal.