1. Air Pollution A brief history of air pollution
Types and sources of air pollutants
Factors that affect air pollution
Air pollution and the urban environment
Acid deposition
Name of Teacher: Bhangare G.N
Subject : Environmental Chemistry
Class : T. Y. B.Sc
Date : 05/09/2018

2. A Brief History of Air Pollution
disastrous London smog event of 1952
smog: smoke and fog;
5 days, nearly 4000 deaths;
Clean Air Act in 1956
Los Angeles: photochemical smog
forms in sunny weather and irritates the eyes
U.S. Clean Air Act, 1970, 1990
set federal emission standards for states to implement
and enforce

3. Types and Sources of Air Pollutants
Air pollutants are airborne substances (either solids,
liquids, or gases) that occur in concentrations high
enough to threaten the health of people and animals,
to harm vegetation and structures, or to toxify a given
environment.
They come from natural sources and human activities:
Natural: dust, volcano, forest fire, ocean waves, …
Human: fixed sources (power plants, homes, …)
mobile sources (cars, ships, …)

4. Principal Air Pollutants
primary and secondary pollutants
particulate matter: a group of solid particles and liquid droplets that are small enough to remain suspended in the air
PM10, PM2.5: <10 or 2.5 micrometer in diameter
Carbon monoxide: colorless, odorless, poisonous
Globally, a large percentage of air pollution sources are natural. Within localized areas, however, human-caused sources are often the largest contributors.

5. Over U.S.

6. Principal Air Pollutants
Volatile organic compounds (VOCs): represent a class of organic compounds that are mainly hydrocarbons – individual organic compounds composed of hydrogen and carbon
nitrogen oxides: nitrogen dioxide (NO2) and nitric oxide (NO), together called NOx
Along with ozone, VOCs and NOx are major components of photochemical smog.
Photochemical smog is a problem on most
major cities of the world.

7. Ozone in the Troposphere
Photochemical smog: in the presence of sunlight
Ozone: unpleasant odor, irritates eyes and hurt human health, reduce crop yield

8. Ozone in the Stratosphere
relationship to ultraviolet radiation
chlorine compounds
chlorofluorocarbons (CFCs); a single
chlorine removes as many as 100,000
ozone molecules
Montreal Protocol
When scientists first measured extremely low ozone values in the Antarctic stratosphere, they thought the instruments were malfunctioning.

9. mainly due to changes in polar stratospheric temperatures
Figure 1: Ozone distribution over the South Pole on September 29, 2006, as measured by ozone monitoring equipment on NASA’s Aura Satellite. Notice that the lowest ozone concentration or ozone hole (purple shades) covers most of Antarctica.
Ozone hole in 2006;
mainly due to changes in
polar stratospheric
temperatures
Figure 1, p. 337

10. Air Pollution: Trends and Patterns
Air Quality Index (AQI): includes the pollutants CO, SO2, NO2, particulate matter, and O3
Secondary air pollutants (e.g., O3)
are particularly difficult to control,
because they are not emitted
directly into the atmosphere.

11. Figure 12.11: The number of unhealthful days (by county) across the United States for any one of the five pollutants (CO, SO2, NO2, O3, and particulate matter) during (Data courtesy of United States Environmental Protection Agency.)
Fig , p. 338

12. Factors affecting air pollution
The role of the wind
dilution
turbulence
mixing
“Dilution is the solution to pollution” - in the 1950s this motto led to the construction of tall smokestacks for large factories. Pollution was released higher in the atmosphere where winds were stronger. Air quality improved locally but suffered downwind.

13. The Role of Stability and Inversions
temperature lapse rates
inversions
mixing depth
The mixing layer can often be
easily seen from an airplane.

14. The Role of Topography cold air drainage
air blockage by mountain ranges

15. Severe Air Pollution Potential
Sources (clustered close together)
high pressure (for inversion and weak wind)
Inversions
Stagnation (unable to disperse pollutants)
A valley (for accumulation of pollutants)
Some locations, like Los Angeles and Mexico City, have an unfortunate combination of surrounding topography, frequent inversions, abundant emissions and plentiful sunlight - perfect conditions for photochemical smog.

16. Air Pollution and the Urban Environment
urban heat island
country breeze

17. Acid Deposition pH wet deposition dry deposition acid fog: SO2 and NOx
acid rain effects
Precipitation pH values