Environmental Engineering

1. Air Pollution
Lecture No. 51

2. Definition
Air pollution may be defined as the
presence in the air (outdoor atmosphere) of
one or more contaminants or combinations
thereof in such quantities and of such
durations as may be or tend to be injurious
to human, animal or plant life, or property,
or which unreasonably interferes with the
comfortable enjoyment of life or property or
conduct of business.

3. Air Pollutant
It is a substance or effect dwelling temporarily or permanently
in the air , which adversely alters the environment by
interfering with the health, the comfort, or the food chain, or
by interfering with the property values of people.
A pollutant can be solid (large or sub-molecular), liquid or
gas .
It may originate from a natural or anthropogenic source (or
both).
It is estimated that anthropogenic sources have changed the
composition of global air by less than 0.01%.
However, it is widely accepted that even a small change can
have a significant adverse effect on the climate, ecosystem
and species on the planet.
Examples of these are acid rain, ozone in the lower
atmosphere, and photochemical smog.

4. Composition of
dry atmosphere, by volume
ppmv: parts per million by volume
Gas Volume
Nitrogen (N2) 780,840 ppmv (78.084%)
Oxygen (O2) 209,460 ppmv (20.946%)
Argon (Ar) 9,340 ppmv (0.9340%)
Carbon dioxide
(CO2)
375 ppmv
Neon (Ne) 18.18 ppmv
Helium (He) 5.24 ppmv
Methane (CH4) 1.745 ppmv
Krypton (Kr) 1.14 ppmv
Hydrogen (H2) 0.55 ppmv
Not included in above dry atmosphere:
Water vapor
(highly variable)
typically 1%
Mean Atmospheric Water Vapor.
Source for figures above: NASA. Carbon dioxide and methane updated (to 1998) by IPCC TAR table 6.1 [1]. The NASA total was 17 ppmv
over 100%, and CO2 was increased here by 15 ppmv. To normalize, N2 should be reduced by about 25 ppmv and O2 by about 7 ppmv.
Minor components of air not listed above include:
Gas Volume
nitrous
oxide
0.5 ppmv
xenon 0.09 ppmv
ozone 0.0 to 0.07 ppmv
nitrogen
dioxide
0.02 ppmv
iodine 0.01 ppmv
carbon
monoxide
trace

8. National Ambient Air Quality Standards
Pollutant Primary Stds. Averaging Times Secondary
Stds.
9 ppm (10
mg/m
3
)
8-hour
1
NoneCarbon Monoxide
35 ppm
(40 mg/m
3
)
1-hour
1
None
Lead 1.5 µg/m
3
Quarterly Average Same as
Primary
Nitrogen Dioxide 0.053 ppm
(100 µg/m
3
)
Annual (Arithmetic
Mean)
Same as
Primary
50 µg/m3
Annual2
(Arith.
Mean)
Same as
Primary
Particulate Matter
(PM10)
150 ug/m
3
24-hour
1
15.0 µg/m
3
Annual
3
(Arith.
Mean)
Same as
Primary
Particulate Matter
(PM2.5)
65 ug/m
3
24-hour
4
Ozone 0.08 ppm 8-hour
5
Same as
Primary
0.03 ppm Annual (Arith. Mean) -------
0.14 ppm 24-hour
1
-------
Sulfur Oxides
------- 3-hour
1
0.5 ppm
(1300 ug/m
3
)
1
Not to be exceeded more than once per year.
2
To attain this standard, the 3-year average of the weighted annual mean PM10 concentration at
each monitor within an area must not exceed 50 ug/m
3
.
3
To attain this standard, the 3-year average of the weighted annual mean PM2.5 concentrations
from single or multiple community-oriented monitors must not exceed 15.0 ug/m
3
.
4
To attain this standard, the 3-year average of the 98th percentile of 24-hour concentrations at
each population-oriented monitor within an area must not exceed 65 ug/m
3
.
5
To attain this standard, the 3-year average of the fourth-highest daily maximum 8-hour average
ozone concentrations measured at each monitor within an area over each year must not exceed
0.08 ppm.

9. Health Effects of Nitrogen
Oxides
• Short-term exposure at concentrations greater than
3 parts per million (ppm) can measurably decrease
lung function.
• Concentrations less than 3 ppm can irritate lungs.
• Concentrations as low as 0.1 ppm cause lung
irritation and measurable decreases in lung function
in asthmatics.
• Long-term lower level exposures can destroy lung
tissue, leading to emphysema.
• Children may also be especially sensitive to the
effects of nitrogen oxides.

10. Other Effects
• Seriously injure vegetation at certain
concentrations. Effects include:
– Bleaching or killing plant tissue.
– Causing leaves to fall.
– Reducing growth rate.
• Deteriorate fabrics and fade dyes.
• Corrode metals (due to nitrate salts formed
from nitrogen oxides).
• Reduce visibility.

11. Other Effects (Continued)
• Oxides of nitrogen, in the presence of
sunlight, can also react with
hydrocarbons, forming photochemical
oxidants or smog.
• Also, NOx is a precursor to acidic
precipitation, which may affect both
terrestrial and aquatic ecosystems.

12. Sulfur Dioxide
Ninety-five percent of pollution related sulfur
oxide emissions are in the form of sulfur
dioxide (SO2), a heavy, colorless gas with an
odor like a struck match.
This gas combines easily with water vapor,
forming aerosols of sulfurous acid (H2SO3), a
colorless, mildly corrosive liquid.
This liquid may then combine with oxygen in
the air, forming the even more irritating and
corrosive sulfuric acid (H2SO4).

13. Other sulfur-containing
compounds
• Hydrogen sulfide (H2S) gas - rotten eggs.
• Mercaptans - skunk spray or decayed
garbage. (Added in trace amounts to natural
gas, providing a leak-detecting warning
odor.)
Note: The amount of SO2 released from coal
fired power plants depends on the sulfur
content of coal, normally 0.7% to 2% by
weight. High sulfur coal sometimes contains
as much as 6% sulfur by weight. In India,
sulfur content is quite low.

14. Health Effects of Sulfur Oxides
• Sulfur dioxide not only has a bad odor, it can irritate
the respiratory system.
• Exposure to high concentrations for short periods of
time can constrict ( to make some thing tight,
smaller or narrower) the bronchi (pipe leading to the
lungs) and increase mucus flow ( nose blocked with
mucus), making breathing difficult.
• Children, the elderly, those with chronic lung
disease (lasting for a long time), and asthmatics (a
chest illness that causes difficult in breathing) are
especially susceptible to these effects.

15. Sulfur dioxide can also:
• Immediately irritate the lung and throat at
concentrations greater than 6 parts per
million (ppm) in many people.
• Impair the respiratory system's defenses
against foreign particles and bacteria, when
exposed to concentrations less than 6 ppm
for longer time periods.
• Apparently enhance the harmful effects of
ozone. (Combinations of the two gases at
concentrations occasionally found in the
ambient air appear to increase airway
resistance to breathing.)

16. Health Effects of Sulfur Oxides
• Sulfur dioxide tends to have more toxic effects when acidic
pollutants, liquid or solid aerosols, and particulates are also present.
(In the past, thousands of excess deaths occurred in areas where SO2
concentrations exceeded 1 ppm for a few days and other pollutants
were also high.) Effects are more pronounced among mouth
breathers, e.g., people who are exercising or who have head colds.
These effects include:
• Health problems, such as episodes ( An event or situation occurring
as a part of a long series of events) of bronchitis requiring
hospitalization associated with lower-level acid concentrations.
• Self-reported respiratory conditions, such as chronic cough and
difficult breathing, associated with acid aerosol concentrations.
(Asthmatic individuals are especially susceptible to these effects.
The elderly and those with chronic respiratory conditions may also
be affected at lower concentrations than the general population.)
• Increased respiratory tract infections, associated with longer term,
lower-level exposures to SO2 and acid aerosols.
• Subjective symptoms, such as headaches and nausea ( A feeling of
wanting to be sick), in the absence of pathological abnormalities, due
to long-term exposure.

17. Sulfur oxides Effects on Plants
• Sulfur dioxide easily injures many plant species and
varieties, both native and cultivated. Some of the
most sensitive plants include various commercially
valuable pines ( A tree that produces cones and has
thin sharp leaves through out the year mostly grow
in cool northern region), legumes ( peas and beans),
red and black oaks ( A tree with tough hard wood
common in many parts of world), white ash, alfalfa
and blackberry. The effects include:
– Visible injury to the most sensitive plants at
exposures as low as 0.12 ppm for 8 hours.
– Visible injury to many other plant types of
intermediate sensitivity at exposures of 0.30 ppm
for 8 hours.
– Positive benefits from low levels, in a very few
species growing on sulfur deficient soils.

18. Other Effects
• Increases in sulfur dioxide concentrations
accelerate the corrosion of metals, probably
through the formation of acids. (SO2 is a
major precursor to acidic deposition.) Sulfur
oxides may also damage stone and masonry,
paint, various fibers, paper, leather, and
electrical components.
• Increased SO2 also contributes to impaired
visibility. Particulate sulfate, much of which
is derived from sulfur dioxide emissions, is a
major component of the complex total
suspended particulate mixture.

19. Health Effects of Ozone
• Ozone acts as a powerful respiratory irritant
at the levels frequently found in most of the
nation's urban areas during summer months.
• Ozone exposure may lead to:
– Shortness of breath.
– Chest pain when inhaling deeply.
– Wheezing and coughing.
Long-term, repeated exposure to high levels
of ozone may lead to large reductions in
lung function, inflammation of the lung
lining, and increased respiratory
discomfort.