Mobile Air Pollution

1. Air Pollution
Mobile Sources

2. The Thin Shell Called the
Atmosphere
•Earth’s atmosphere is a thin
layer of gas held around the
surface by gravity.
•90% of the atmosphere’s
mass is within 15 km of the
earth’s surface
–Earth's radius is about
6400 km
–The atmosphere is like a
layer of paint on a
basketball

3. Composition of the Atmosphere

4. Origin of the Atmosphere
•Earth’s primitive atmosphere consisted mainly of
CO
2
released by volcanic eruptions
•About 3.5 billion years ago, photosynthesizing
algae (stromatolites) began to release oxygen
which steadily increased over time.
•This was the first global air pollution crisis
because oxygen was poisonous to life forms that
existed before photosynthesis.
•Lead to major extinction event 2.2 billion years
ago (Great Oxygen Crises).

5. Origin of the Atmosphere
•Volcanic eruptions also release trace amounts NH
3
(ammonia).
•N
2
is formed from the reaction between NH
3
and
oxygen in the atmosphere.
•The high percentage of nitrogen in today’s
atmosphere is because N
2
is not chemically active
with other molecules in the atmosphere.
•Conversely, the amount of O
2
in the atmosphere is
limited because it is very reactive with other
molecules in Combustion, Decomposition, and
Respiration

6. What is an Air Pollutant?
•An air pollutant is anything in the
atmosphere that is hazardous to life or the
environment
•Primary pollutant – one that is emitted
directly into the atmosphere by the source
•Secondary pollutant – one that not
emitted directly, but is generated through
chemical reactions over time from material
emitted by the source

7. Air Pollutants Sources
Primary Pollutants
Secondary Pollutants
Sources
Natural
Stationary
COCO
2
SO
2
NONO
2
VOCs
Particles
SO
3
HNO
3H
2
SO
4
O
3
PANs
Mobile
NO
2

8. Air Pollution
•Natural sources of air pollution are
sources not caused by people or their
activities.
–An erupting volcano emits particulate matter
and gases
–Forest and prairie fires can emit large
quantities of pollutants
–Plants and trees emit hydrocarbons
–Dust storms can create large amounts of
particulate matter.

9. Human Air Pollution
•A mobile source of air pollution refers to
a source that is capable of moving under
its own power.
•A stationary source of air pollution refers
to an emission source that does not move
(i.e., power plants, chemical and
manufacturing industries).

10. Air Pollution Standards
•The Clean Air Act (1970), which was last
amended in 1990, requires EPA to set National
Ambient Air Quality Standards (NAAQS) for
wide-spread pollutants from numerous and
diverse sources considered harmful to public
health and the environment.
•EPA has set NAAQS for six principal pollutants,
which are called "criteria" pollutants (see next
slide).
–Units of measure for the standards are parts per
million (ppm) by volume, milligrams per cubic meter of
air (mg/m3), and micrograms per cubic meter of air
(µg/m3).

11. Table 8-5, p. 268

12. Air Pollution Standards
•The Clean Air Act established two types of
national air quality standards.
•Primary Standards set limits to protect
public health, including the health of
"sensitive" populations such as
asthmatics, children, and the elderly.
•Secondary Standards set limits to protect
public welfare, including protection against
visibility impairment, damage to animals,
crops, vegetation, and buildings.

13. The Good News
•National air quality levels measured at
thousands of monitoring stations across
the country have shown improvements
over the past 20 years for all six principal
pollutants.
•Since 1970, aggregate emissions of the
six principal pollutants have been cut 48
percent.

14. The Good News

15. The Not So Good News
•Despite this progress, about 160 million tons of
pollution are emitted into the air each year in the
United States.
•Approximately 146 million people live in counties
where monitored air in 2002 was unhealthy at
times because of high levels of at least one of
the six principal air pollutants.
•The vast majority of areas that experienced
unhealthy air did so because of one or both of
two pollutants—ozone and particulate matter
(PM).

16. Vehicle Sources of Pollution
•Main problem: Gasoline and diesel fuels
are mixtures of hydrocarbon compounds
which contain hydrogen and carbon
atoms. These atoms combine with
oxygen during combustion.
•Also contain additives such as lead.
•Nitrogen atoms are also present and are
combined with oxygen to produce gases.

17. Mobile Sources of Pollution
•Primary Pollutants from Engine
Combustion
–Carbon Monoxide (CO)
–Lead (Pb)
–Hydrocarbons (VOCs)
–Nitrogen Oxides (NOX)
•Secondary Pollutants from Engine
Combustion
–Nitrogen Dioxide (NO
2
)
–Ozone (O
3
)

18. Carbon Monoxide (CO)
•Colorless and odorless gas
•Most abundant air pollutant
•Major source (~ 77%) is motor vehicle
exhaust
•Poorly running automobiles emit large
amounts by incomplete combustion
(low temperatures an/or not enough O
2
in engine).

19. Carbon Monoxide (CO)
•Extremely toxic – causes heart
disease long-term, or death within an
hour if concentration is 1600 ppm or
more
•Hemoglobin in the blood is 200 times
more attracted to carbon monoxide
than oxygen (leading to oxygen
starvation of the body)
•Most hazardous to human health of all
criteria pollutants

20. Lead
•Lead is a metal found naturally in the
environment as well as in manufactured
products.
•The major sources of lead emissions have
historically been motor vehicles (such as
cars and trucks) and industrial sources.
•Due to the phase out of leaded gasoline,
metals processing is the major source of
lead emissions to the air today.
•Exposure results in brain damage and
memory loss, as well as low IQ in children

21. Volatile Organic Compounds
(VOCs)
•The term VOC stands for volatile organic
compounds.
•Also called hydrocarbons, entirely made of
carbon and hydrogen atoms
•VOCs are carbon-containing chemicals that
evaporate easily at room temperature.
•Usually gasoline vapors and uncombusted fuel.
•No direct adverse health effects, but they react
with other substances to form smog

22. Nitrogen Oxides (NO
x
)
•Nitrogen oxides, or NOx, is the generic
term for a group of highly reactive gases,
all of which contain nitrogen and oxygen
in varying amounts.
•The primary manmade sources of NOx
are motor vehicles.
•Due to the high temperatures and oxygen
in a vehicle engine, N separates from N
2

and combines with O
2
to form NOx

23. Nitrogen Dioxide (NO
2
)
•Can be emitted directly as a primary
pollutant, but most is created by the
oxidation of Nitric Oxide (NO)
•Toxic gas that has a pungent odor and
gives the air a yellow to reddish-brown color
•Corrosive and can react with other
substances to produce other secondary
pollutants
•Irritates the lungs and can reduce immunity
to infection at high levels
•Breaks down readily, so at its highest levels
when traffic levels are the highest

24. Ozone
•At the surface, ozone (O
3
) is a pollutant - it
irritates the respiratory system and damages
plants
•Component of Photochemical Smog
•Created differently than it is produced in the
stratosphere
•VOC + NOx + Heat + Sunlight = Ozone
•Motor vehicle exhaust and industrial emissions,
gasoline vapors, and chemical solvents are
some of the major sources of NOx and VOC that
help to form ozone.

25. Smog
A combination of the words “smoke” and
“fog”
Two different types of smog occur
•Photochemical smog; dry air smog
with ozone, peroxyacyl nitrate (PAN)
and formaldehyde (see previous
lecture)
•Classic (London) Smog: original
meaning of smog; mixture of smoke,
sulfurous particles and soot with a fog

26. Photochemical Smog
•Occurs on sunny days due to intense
traffic.
•Oxides of nitrogen and hydrocarbons
react in the presence of sunlight to
produce a mixture of aerosols and gases.
•Photochemical smog contains ozone,
ketones, formaldehyde, and PAN
(peroxyacetyl nitrates).
•The next slides illustrates the chemical
reactions

28. Photochemical Smog
Peak Smog Hours

29. The Summertime Pollutant
•Peak ozone levels typically occur during
hot, dry, stagnant summertime conditions.
•The length of the ozone season varies
from one area of the United States to
another.
•Southern and Southwestern states may
have an ozone season that lasts nearly
the entire year.

30. Photochemical Smog: Health Effects
•Increased incidents of respiratory
distress.
•Repeated exposures to ozone:
–Increased susceptibility to respiratory
infection
–Lung inflammation
–Aggravation of pre-existing respiratory
diseases such as asthma.
–Decreases in lung function and increased
respiratory symptoms such as chest pain and
cough.

31. Automobile Emission
Control Strategies

32. Automobile Emission
Control Strategies
•CO Reduction
–Increase O2 to the combustion chamber from the
carburetor.
–Higher air-to-fuel ratio
–CO
2 instead of CO from exhaust.
•VOC Reduction
–Capture unburned vapors from fuel tank and
carburetor using Charcoal Filters
–Recycle VOC back into the combustion chamber via
the ERG valve.
–Increase combustion temperatures

33. Automobile Emission
Control Strategies
•Problem: Higher air to fuel ratios (CO
reduction) and and higher temperatures
(VOC reduction) increase the amount of
NOx emitted via engine exhaust.
•Solution: catalytic converter

34. What is a catalytic converter (CC)?
•A device that promotes (catalyzes)
reactions in order to convert HC, CO, and
NO
x
into less harmful compounds before
they exit the vehicle.
–HC + O
2
 CO
2

+ H
2
O (oxidation)
–2CO + O
2
 2CO
2
(oxidation)
–2NO  N
2
+ O
2
or 2NO
2
 N
2
+ 2O
2
(reduction)
•The catalyst in most CCs is Platinum
which is why CCs are so expensive.

35. Are Catalytic Converters the Answer?
•Until recently, it was thought that catalytic
converters offered the greatest potential
for decreasing mobile source pollution.
•The newest-model cars can remove up to
95% of the emissions.
•However, mobile source pollution still a
problem because of the ever increasing
number of vehicles.
•Real improvements in vehicle emissions
will come from a switch from gasoline as a
fuel and from reductions in the number of
vehicles and miles driven.