i. i.air pollution – sources & effects most local air pollution associated with cities, esp....
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I. Air Pollution – Sources & Effects
• Most local air pollution associated with cities, esp. large cities and industrial centers
• Average concentration of airborne particles in urban areas ~10x concentration in rural areas
• Major cities – air pollution causes thousands of deaths each year
• Los Angeles – 6000• New York – 4000• Detroit – 2000
• Mexico City – Air quality so severe that some people estimate breathing is equivalent to smoking two packs of cigarettes a day
• Many air pollutants are hygroscopic• Combine with water and promote fog formation
• Particulate matter can affect local precipitation• Boulder, CO – Power plant produced fly ash aerosols and
induced snowfall
II. Air Pollution – Components
• Primary• Problematic in the form in which they’re produced• Ex – Lead, carbon monoxide
• Secondary• Require modification• Ex – Ozone• Many are components of photochemical smog
(react chemically with light)
• Legislation addressing air pollution requires consideration of both primary and secondary pollutants
• Clean Air Act – 1970• Clean Air Act Amendments – 1990
• EPA – NAAQS for six criteria pollutants
II. Air Pollution – Components
A. Particulate Matter1. Sources
• Combustion of fossil fuels, especially coal• Mobile sources – Cars, trucks• Stationary sources – Power plants, industrial furnaces,
wood stoves
2. Effects• By the 1950s, air quality in London had deteriorated so
much that incidences of death due to pollution weren’t uncommon
• 1952 – “Killer Smog” in London 4000+ deaths• Health – Respiratory impairment, lung damage, lung
cancer• Especially children, elderly, people with chronic
respiratory problems• Acidic PM can damage structures, reduce visibility
II. Air Pollution – Components
A. Particulate Matter3. Trends
• EPA Standards• Pre-1987 – TSP (Total Suspended Particulates)• Post-1987 – PM10 (Particles < 10 μm)
• Post-1997 – PM2.5 (Particles < 2.5 μm)
• NAAQS for PM10
• Annual average = 50 μg m-3 (revoked Dec 2006)• Daily peak = 150 μg m-3
• NAAQS for PM2.5
• Annual average = 15 μg m-3
• Daily peak = 35 μg m-3
http://www.epa.gov/air/airtrends1990-2009: Direct PM2.5 emissions down 50%
1990-2009: Direct PM10 emissions down 67%
II. Air Pollution – Components
B. Carbon Monoxide• Colorless, odorless gas• Produced by incomplete combustion of fossil fuels
(too little O2 supplied in a normally tuned engine)1. Sources
• About 56% of CO emissions nationwide from on-road motor vehicles (24% from non-road vehicles)
• In cities, 85-95% of CO from motor vehicles• Diesel engines typically produce less CO but more PM
than gasoline engines• Alternative to complete combustion of fuel is
combustion of exhaust• Produces hazardous amounts of heat• Combustion temperature can be lowered using
catalyst• Chemical catalysts poisoned by lead
II. Air Pollution – Components
B. Carbon Monoxide2. Effects
• CO binds to hemoglobin in place of oxygen• Affinity for CO ~ 200x higher than for O2
• Continued exposure can lead to• Impairment of vision• Difficulty estimating time• Reduced manual dexterity• Poor learning ability• Difficulty performing complex tasks• Greater risk of heart attacks in people with
certain forms of heart disease (e.g. angina)• Contributes to formation of ground-level ozone
II. Air Pollution – Components
C. Nitrogen Oxides (NOx)• Principally NO2
• Highly reactive reddish-brown gas
• Play a major role in the formation of ozone, PM, haze and acid rain
• Important component of photochemical smog
1. Sources• Forms from FF combustion at high temperatures
• Mobile – Cars & trucks (58%)• Stationary – Power plants (34%), home heaters, gas
stoves, industrial plants (8% total)• Formation could be controlled by using pure
oxygen for combustion (impractical and dangerous)• Formation reduced by low-temperature combustion
II. Air Pollution – Components
C. Nitrogen Oxides (NOx)2. Effects
• Strong oxidizing agent• Reacts readily in air to form nitric acid and nitrates
• Health• Irritates lungs and lower resistance to respiratory
infections• Lung damage
• Environment• Damages plant foliage, impairs growth• Precursor of ground-level ozone, PM, smog• Contributes to acid rain - Leaching of minerals from soil - Acidification of lakes and waterways• Contributes to eutrophication of lakes & waterways• Contributes to global warming (N2O)