15.6 – NOTES Air Pollution

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

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

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

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

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

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

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

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

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

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

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

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?

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

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

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

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 10-40 km above Earth’s surface

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

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

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

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

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