1. 15.6 – NOTES Air Pollution

2. Most air pollutants result from fossil-fuel based energy production
Some consequences of air pollution include smelly/ugly air, corroded buildings/machines, weak livestock, stunted crops

3. D.1 Sources of Air Pollution
Some are the result of natural processes
These processes include volcanoes and forest fires
Human pollution is in more concentrated areas

4. Primary air pollutants
Pollutants that directly enter the atmosphere
Methane
CH4 produced from fossil fuels and anaerobic bacteria
Volatile organic compounds (VOCs)
Hydrocarbons that easily evaporate or are gases at room temperature
Often come from unburned gasoline
One of the primary components of smog

6. Secondary air pollutants
Formed in atmosphere by reactions between primary air pollutants and natural air components

7. Particulate pollution
Microscopic particles that enter the air from human activities (production) or natural processes (fire, volcano, wind erosion)
Primarily comes from smokestacks
Synthetic substances
Human caused
Chlorofluorocarbons (CFCs)
There is no natural sources of stratospheric fluorine, so humans are the only source for this pollutant

8. D.2 Identifying Major Air Contaminants
Automobile use contributes to half the total mass of human generated air contaminants

9. D.3 Smog: Hazardous to Your Health
The words comes from a combination of the words smoke and fog
Cause by weather conditions interacting with air conditions
Can endanger health
Responsible for deaths in London and PA in the 1950s
EPA has developed air quality index that contribute to smog in major metro areas
Fatalities may be higher than predicted due to synergistic interactions
Combined effect of several substances is greater than the sum of their separate effects

12. Photochemical smog
Different from industrial smog
Caused by hydrocarbon interaction with sunlight and other weather conditions

13. Temperature inversion
Occurs when cool air mass is trapped beneath a less dense warm air mass
Pollutants cannot escape, which leads to photochemical smog
Reacts with ozone on the ground
Ozone at ground level can cause chest pain, shortness of breath, throat irritation, coughing
It can also worsen chronic respiratory diseases

14. D.4 Vehicles and Smog
During the day, different pollutants peak at different times
Morning rush hour (6am – 9am) accounts for the peaks of the majority of pollutants that cause photochemical smog, including NO, NO2, and hydrocarbons
There are no real peak for evening rush house because people leave at different times

15. D.5 Stationary Source Pollution Control and Prevention
Several options to prevent/limit pollution from stationary sources
Use technologies that don’t use combustion
Use more energy conservation measures to get more energy from the initial source
Remove potentially harmful substances before burning the fuel
More completely burned/oxidized fuel
Remove pollutants after combustion

16. All options require more cost- need to look at measures
What would the prevention or control measure cost?
What benefits would it offer?
What costs or risks would be involved in not using the prevention or control measures?

17. Electrostatic precipitation
Most common technique used to control particulate pollutants
Waste passes through an electrical field, become charged, and collects on a plate
Mechanical filtering
Like a big vacuum cleaner
Scrubbing
Controls particles and sulfur oxides
Wet scrubbing
Removes SO2 by using an aqueous solution of Ca(OH)2, called limewater

19. D.7 Controlling Automobile Emissions
Clean Air Act of 1970 authorized the EPA to set emissions standards for new vehicles
This lead to the development and use of the catalytic converter
Exhaust gases and outside air pass over solid catalysts that speed conversion of harmful gases to harmless products
Catalysts are not used up in the reaction

20. Collision theory
Reactions can occur only if molecules collide with sufficient energy to disrupt bonds and break them
Activation energy
Minimum energy required for such effective collisions
Energy needed for reaction to occur
Catalysts provide a different activation energy

21. D.8 Ozone and CFCs: A Continued Success Story
UVA and B are needed for vitamin D production in small amounts
Too much UVB and C cause problems, including skin cancer
Ozone layer
Absorbs UV radiation from sun
3mm thick, and found km above Earth’s surface

22. Research suggests that for every 1% reduction of the ozone layer, there will be an increase of 2-5% in skin cancers
It can also lower crop production, increase sunburns and cataract, and damage some aquatic plants.
Free Radicals
Atoms that contain unstable arrangements that very reactive and have an odd number of electrons
Oxygen free radicals react with the oxygen gas in the stratosphere to form ozone

24. Ozone depletion
CFCs were widely used for a variety of things, including cooling fluids, aerosol propellants, and cleaning solvents
Structure of a CFC

25. In the 1970s, two chemists proposed that CFCs were a threat to the ozone layer
A satellite launched a few years later showed that there was a hole in the ozone layer above Antarctica
Evidence showed that these CFCs, when hit by solar radiation, lose one of their chlorine atoms, which turns into a chlorine free radical ( Cl● )
The chlorine free radical attacks an ozone molecule, causing one of the oxygen atoms to create chlorine monoxide and oxygen gas, in place of the ozone
Another oxygen atom will run into the chlorine monoxide molecule, taking the oxygen away to form another oxygen gas molecule, and leaving the chlorine as a free radical to attack another ozone molecule

26. Montreal Protocol
An agreement signed in 1987 by the United States and 55 other countries
Formally known as The Montreal Protocol on Substances that Deplete the Ozone Layer
Called for an end to CFC production and development of substitute materials to replace CFCs

27. HCFC molecules
Hydrochlorofluorocarbons
Advantage: replace one of the chlorine atoms with hydrogen, so fewer chlorine free radicals are produced
Disadvantage: still produce chlorine free radicals, greenhouse gas
HFC molecules
Hydrofluorocarbons
Contain only hydrogen, fluorine, and carbon, so no chlorine free radicals
Can help decompose themselves