1. Air Pollution and Stratospheric Ozone Depletion
Chapter 15
Air Pollution and Stratospheric Ozone Depletion

2. Major Air Pollutants and Their Sources
Module 46
Major Air Pollutants and Their Sources
Learning Objectives
After this module, you should be able to:
identify and describe the major air pollutants.
describe the sources of air pollution.

3. Air Pollution is a global system
Air pollution: The introduction of chemicals, particulate matter, or microorganisms into the atmosphere at concentrations high enough to harm plants, animals, and materials such as buildings, or to alter ecosystems.
Air pollution can be complex:
It has many inputs and outputs (automobiles, airplanes, factories, power plants, vegetation, soil, volcanoes).
It can travel great distances from the sources and can mix to create new substances while in the air.

4. Classifying Pollutants

5. Classifying Pollutants
Sulfur dioxide (S02):
About 1/3 of SO2 in the atmosphere occurs naturally through the sulfur cycle (volcanoes, forest fires).
2/3 come from human sources, mostly combustion of coal containing iron sulfide and from oil refining and smelting of sulfide ores.
FeS2 + O2  Fe2O3 + SO2
SO2 reacts with water vapor in the air to form sulfuric acid (H2SO4) which is a component of acid deposition.

6. Classifying Pollutants
Nitrogen Oxides (NOx): 
Forms when nitrogen and oxygen gas in air react at high temperatures in automobile engines and coal-burning plants. It can also form from lightning and certain soil bacteria.
NO reacts with oxygen in the air to form NO2
NO2 reacts with water vapor in the air to form nitric acid (HNO3) which is a component of acid deposition.
An ozone precursor, both NO and NO2 play a role in the formation of smog.

7. Classifying Pollutants
Carbon Oxides (COx):
Carbon monoxide (CO) is a highly toxic gas that forms during the incomplete combustion (not enough oxygen) of carbon-containing materials.
Carbon dioxide (CO2) is a major component of the carbon cycle
90% of carbon dioxide (CO2) in the troposphere occurs as a result of the carbon cycle
10% of CO2 in the troposphere occurs as a result of human activities (mostly burning fossil fuels)
Was recently added to the list of regulated pollutants under the U.S. Clean Air Act.

8. Classifying Pollutants
Particulate matter (PM): A variety of solid particles small and light enough to remain suspended in the air. Also known as Particulates.
Haze: Reduced visibility.
Natural sources – forest fires, volcanoes, dust storms
Human sources – combustion of various materials

9. Classifying Pollutants
The most harmful forms of particulate matter are fine particles (PM-10, with an average diameter < 10 micrometers) and ultrafine particles (PM-2.5).
Normal human lungs
Lungs of a smoker

10. Classifying Pollutants
Ozone (O3):
An unstable and highly reactive form of oxygen
Stratospheric ozone – “good” ozone that protects us from damaging UV radiation
Ground level ozone – “bad” ozone that is a major component of photochemical smog
Solar radiation splits an O off of NO2 that bonds to an O2 molecule to create O3

11. Classifying Pollutants
Lead: 
A natural element that was formerly used as an additive in gasoline.
Also enters atmosphere from burning oil, coal, and the peeling/chipping of old paint.

12. Classifying Pollutants
Volatile organic compound (VOC): Are organic chemicals that vaporize easily (at room temp.) and enter the atmosphere.
VOCs are widely used in household chemicals
Cleaners, disinfectors, paints, fuels, etc.
VOCs are also used as industrial solvents
A precursor to ozone formation.

13. Classifying Pollutants

14. Primary and Secondary Pollutants
Primary pollutant: substance emitted into the air from of a smokestack, exhaust pipe, or natural source.
Secondary pollutant: primary pollutants react with one another or with other chemicals in the air to form new chemicals.
These reactions require a number of factors including sunlight, water (clouds), and the appropriate temperature.

15. Air pollution comes from both natural and human sources
Natural sources:
Dust blown by wind
Pollutants from fires and volcanoes
Volatile organics released by plants
Anthropogenic sources:
Stationary sources – power plants, factories,
incinerators, wood burning stoves
Mobile sources – motor vehicles, farm equipment

16. Anthropogenic Emissions
In the U.S., emissions from human activity are monitored, regulated, and in many cases controlled.
The Clean Air Act (CAA) and its various amendments require that EPA establish standards to control pollutants that are harmful to “human health and welfare”.
Aggregate emissions of six common pollutants dropped 69% between 1970 and 2014.

17. The Clean Air Act
In 1970, Congress passed The Clean Air Act (CAA) and created the Environmental Protection Agency (EPA) to enforce it.
The Clean Air Act was most recently
amended in 1990
National Ambient Air Quality Standards (NAAQS) are established to regulate six major pollutants.
Primary standards – protects human health
Secondary standards – prevents environmental and property damage
The EPA also establishes standards for 188 other hazardous air pollutants (or HAPs)
Mostly chlorinated hydrocarbons, VOC’s, and toxic metals

18. The Clean Air Act
How do you remember the six outdoor criteria pollutants regulated by the National Ambient Air Quality Standards (NAAQS)?
NOSCLP – A nose clip will save you from air pollution
Nitrogen oxides
Ozone
Sulfur dioxide
Carbon oxides
Lead
Particulate matter

19. The Clean Air Act
The specific ways to regulate air pollutants can vary:
To help reduce SO2 emissions, the 1990 amendment to the Clean Air Act authorized an emission trading or cap-and-trade program.
Enables the 110 most polluting power plants to buy and sell SO2 pollution rights among each other.
The trading system has greatly reduced emissions
Sulfur dioxide emissions are down 81%
The program has cost less than 10% of original industry projections
The same system is being talked about to combat NO2 and CO2 emissions.

20. The Clean Air Act
Nationally, concentrations of the criteria air pollutants have dropped significantly since 1990:
NO2 ↓54%
O3 ↓22%
SO2 ↓81%
CO ↓77%
Pb ↓99%
PM10 ↓39%
PM2.5 ↓37%

21. The Clean Air Act Can Be Improved
The CAA has been greatly successful, but scientists still point out several deficiencies:
The U.S. still relies on cleanup rather than prevention
Regulation of emissions from motorcycles and two-cycle engines remains inadequate
There is little or no regulation of air pollution from oceangoing ships in American ports
Airports are exempt from many air pollution regulations
The CAA does not regulate CO2 which is a major greenhouse gas
Urban O3 levels too high
It fails to seriously deal with indoor air pollution
Overall, there is a need for better enforcement of the Clean Air Act.