Chapter 19 Air Pollution
Air: The Endangered Global Commons • Mixture of gases: 78% Nitrogen, 21% Oxygen, 0.04% Carbon Dioxide, and others • Contains water vapor and various pollutants • A renewable resource cleansed by natural processes and regenerated by living things • Used by many and protected by few – it suffers from the tragedy that befalls many commons
Anthropogenic Pollutants • Generally create long-term threat • Power plants, automobiles, factories, and other human sources emit large quantities in restricted areas • Higher concern because it is produced in localized regions so that concentrations reach potentially dangerous levels
Core Case Study: When Is a Lichen Like a Canary? • Lichens can warn us of bad air because they absorb air as a source of nourishment. Figure 19-1
Core Case Study: When Is a Lichen Like a Canary? • Some lichen species are sensitive to specific air-polluting chemicals. • After Chernobyl, more than 70,000 reindeer had to be killed because they ate highly radioactive lichens. • Because lichens are widespread, long-lived, and anchored in place, they can help track pollution to its source.
Case study: Isle Royale, MI • Evernia lichens sicken or die in the presence of excess sulfur dioxide • Scientists used Evernia to show evidence of sulfur dioxide pollution entering Isle Royale from coal-burning facilities at Thunder Bay, Ontario
STRUCTURE AND SCIENCE OF THE ATMOSPHERE • The atmosphere consists of several layers with different temperatures, pressures, and compositions. Figure 19-2
Atmospheric pressure (millibars) Temperature Pressure Thermosphere Mesopause Heating via ozone Mesosphere Altitude (kilometers) Altitude (miles) Stratopause Stratosphere Tropopause Ozone “layer” Heating from the earth Troposphere Pressure = 1,000 millibars at ground level (Sea level) Temperature (˚C) Fig. 19-2, p. 440
STRUCTURE AND SCIENCE OF THE ATMOSPHERE • The atmosphere’s innermost layer (troposphere) is made up mostly of nitrogen and oxygen, with smaller amounts of water vapor and CO2. • Ozone in the atmosphere’s second layer (stratosphere) filters out most of the sun’s UV radiation that is harmful to us and most other species.
AIR POLLUTION • Some primary air pollutants may react with one another or with other chemicals in the air to form secondary air pollutants. Figure 19-3
Primary Pollutants Secondary Pollutants CO CO2 SO2 NO NO2 SO3 Most hydrocarbons HNO3 H3SO4 Most suspended particles H2O2 O3 PANs Most NO3– and SO42– salts Natural Stationary Sources Mobile Fig. 19-3, p. 442
Major Air Pollutants • Carbon oxides: • Carbon monoxide (CO) is a highly toxic gas that forms during the incomplete combustion of carbon-containing materials. • 93% of carbon dioxide (CO2) in the troposphere occurs as a result of the carbon cycle. • 7% of CO2 in the troposphere occurs as a result of human activities (mostly burning fossil fuels). • It is not regulated as a pollutant under the U.S. Clean Air Act.
Major Air Pollutants • Nitrogen oxides and nitric acid: • Nitrogen oxide (NO) forms when nitrogen and oxygen gas in air react at the high-combustion temperatures in automobile engines and coal-burning plants. NO can also form from lightening and certain soil bacteria. • NO reacts with air to form NO2. • NO2 reacts with water vapor in the air to form nitric acid (HNO3) and nitrate salts (NO3-) which are components of acid deposition.
Major Air Pollutants • Sulfur dioxide (SO2)andsulfuric acid: • About one-third of SO2 in the troposphere occurs naturally through the sulfur cycle. • Two-thirds come from human sources, mostly combustion (S+ O2 SO2) of sulfur-containing coal and from oil refining and smelting of sulfide ores. • SO2 in the atmosphere can be converted to sulfuric acid (H2SO4) and sulfate salts (SO42-) that return to earth as a component of acid deposition.
Major Air Pollutants • Suspended particulate matter (SPM): • Consists of a variety of solid particles and liquid droplets small and light enough to remain suspended in the air. • The most harmful forms of SPM are fine particles (PM-10, with an average diameter < 10 micrometers) and ultrafine particles (PM-2.5). • According to the EPA, SPM is responsible for about 60,000 premature deaths a year in the U.S.
Major Air Pollutants • Ozone (O3): • Is a highly reactive gas that is a major component of photochemical smog. • It can • Cause and aggravate respiratory illness. • Can aggravate heart disease. • Damage plants, rubber in tires, fabrics, and paints.
Major Air Pollutants • Volatile organic compounds (VOCs): • Most are hydorcarbons emitted by the leaves of many plants and methane. • About two thirds of global methane emissions comes from human sources. • Other VOCs include industrial solvents such as trichlorethylene (TCE), benzene, and vinyl chloride. • Long-term exposure to benzene can cause cancer, blood disorders, and immune system damage.
Major Air Pollutants • Radon (Rn): • Is a naturally occurring radioactive gas found in some types of soil and rock. • It can seep into homes and buildings sitting above such deposits.
URBAN OUTDOOR AIR POLLUTION • Industrial smog is a mixture of sulfur dioxide, droplets of sulfuric acid, and a variety of suspended solid particles emitted mostly by burning coal. • In most developed countries where coal and heavy oil is burned, industrial smog is not a problem due to reasonably good pollution control or with tall smokestacks that transfer the pollutant to rural areas.
Case Study: South Asia’s Massive Brown Cloud • A huge dark brown cloud of industrial smog, caused by coal-burning in countries such as China and India, stretches over much of southeastern Asia. • In areas beneath the cloud, photosynthesis is reduced interfering with crop development. • Fine particles and droplets in the cloud appear to be changing regional climates (including rainfall). • May have contributed to floods in 2002 and 2005 which killed thousands of people.
Sunlight plus Cars Equals Photochemical Smog • Photochemical smog is a mixture of air pollutants formed by the reaction of nitrogen oxides and volatile organic hydrocarbons under the influence of sunlight.
Sunlight plus Cars Equals Photochemical Smog • Mexico City is one of the many cities in sunny, warm, dry climates with many motor vehicles that suffer from photochemical smog. Figure 19-4
Factors Reducing Levels of Outdoor Air Pollution • Settling out – heavier particles settle • Rain and snow – cleanse the air pollutant • Salty sea spray – wash out particulates and water-soluble pollutants • Winds – sweep away and dilute with cleaner air • Chemical reactions – formation of acid rain – chemical falls to Earth The pollutants do not disappear; they are merely shifted elsewhere or deposited onto other medium
Factors Increasing Levels of Outdoor Air Pollution • Urban buildings – slow wind speed • Hills and mountains – reduce flow of air in valleys • Higher temperatures – promote chemical reactions • VOC emissions from certain trees and plants • Grasshopper effect – volatile air pollutants transported from tropics and temperate forests toward the poles during the winter • Temperature inversions – cause buildup
Grasshopper Effect • Explains sightings of reddish-brown haze over the Arctic • Polar bears, whale sharks, and other top carnivores in Arctic have high levels of DDT, other persistent pesticides, toxic metals, and PCBs in their bodies
Temperature Inversions • Cold, cloudy weather in a valley surrounded by mountains can trap air pollutants (left). • Areas with sunny climate, light winds, mountains on three sides and an ocean on the other (right) are susceptible to inversions. Figure 19-5
During normal conditions, air temperature decreases with altitude, thus pollutants ascend and mix with atmospheric gases In a temperature inversion, however, warm air forms a lid over cooler air, thus trapping air pollution
San Diego, CA Inversion layer Inversion layer Fig. 19-5, p. 447
City with several million people and motor vehicles in an area with a sunny climate, light winds, mountains on three sides, and the ocean on the other side – conditions ideal for photochemical smog worsened by frequent thermal inversions – example: Los Angeles, CA (Brown-air smog)
Brown-air cities • Early morning traffic provides the ingredients for photochemical smog • Reaches highest levels in early afternoon • Suburbs and surrounding rural areas usually have higher levels of photochemical smog than the cities themselves • Major episodes usually occur during summer
Although anthropogenic pollutants are the most significant sources of air pollution, researchers have found some instances in which naturally occurring pollutants noticeably affect air quality. In Atlanta, the trees emit a number of highly reactive hydrocarbons. These chemicals react with nitrogen dioxide from automobiles and other combustion sources to produce ozone. New research shows that hydrocarbons from trees are 50 to 100 times more reactive than hydrocarbons from human sources.
ACID DEPOSITION • Sulfur dioxides, nitrogen oxides, and particulates can react in the atmosphere to produce acidic chemicals that can travel long distances before returning to the earth’s surface. • Tall smokestacks reduce local air pollution but can increase regional air pollution.
ACID DEPOSITION • Acid deposition consists of rain, snow, dust, or gas with a pH lower than 5.6. Figure 19-6
Wind Transformation to sulfuric acid (H2SO4) and nitric acid (HNO3) Windborne ammonia gas and particles of cultivated soil partially neutralize acids and form dry sulfate and nitrate salts Wet acid depostion (droplets of H2SO4 and HNO3 dissolved in rain and snow) Nitric oxide (NO) Sulfur dioxide (SO2) and NO Dry acid deposition (sulfur dioxide gas and particles of sulfate and nitrate salts) Acid fog Farm Lakes in shallow soil low in limestone become acidic Ocean Lakes in deep soil high in limestone are buffered Fig. 19-6, p. 448
Harmful Effects of Acid Rain • Cause or worsen respiratory disease • Attack metallic and stone objects • Decrease atmosphere visibility • Kill fish • Deplete soils of vital plant nutrients • Harm crops and plants
ACID DEPOSITION • Acid deposition contributes to chronic respiratory disease and can leach toxic metals (such as lead and mercury) from soils and rocks into acidic lakes used as sources for drinking water.
ACID DEPOSITION • Air pollution is one of several interacting stresses that can damage, weaken, or kill trees and pollute surface and groundwater. Figure 19-9
Emissions SO2 NOx Acid deposition H2O2 O3 Others PANs Susceptibility to drought, extreme cold, insects, mosses, & disease organisms Reduced photo-synthesis and growth Direct damage to leaves & bark Tree death Soil acidification Reduced nutrient & water uptake Root damage Leaching of soil nutrients Release of toxic metal ions Acids Lake Groundwater Fig. 19-9, p. 451
Acid deposition effect on aquatic ecosystems • Fish die if pH drops below 4.5 • Aluminum ions are released from soil, carried into lakes, can clog fish gills • Mercury buildup in fish can affect humans (kidneys, brain) Note: acid rain can be buffered by limestone, which reduces acidity
Factors which determine how severe the health effects are from mercury exposure • The chemical form of mercury • The dose • The age of person exposed (fetus most susceptible) • The duration of exposure • The route of exposure – inhalation, ingestion, dermal contact, etc. • The health of the person exposed
Methylmercury effects on humans • Impaired neurological development (fetuses, infants, children) • Impacts on cognitive thinking, memory, attention • Impaired peripheral vision • Disturbances in sensations (“pins and needles” feelings) • Impairment of speech, hearing, walking
Acid deposition effect on plants • Tree leaves, needles damaged • Important nutrients (Ca, Mg) leached, reducing plant productivity • Aluminum ions are mobilized, reduce plant productivity • Lead, cadmium, mercury are mobilized, reduce plant productivity • Plants weakened and become susceptible to other disease
Solutions Acid Deposition Prevention Cleanup Reduce air pollution by improving energy efficiency Add lime to neutralize acidified lakes Reduce coal use Add phosphate fertilizer to neutralize acidified lakes Increase natural gas use Increase use of renewable energy resources Burn low-sulfur coal Remove SO2 particulates & NOx from smokestack gases Remove NOx from motor vehicular exhaust Tax emissions of SO2 Fig. 19-10, p. 452
INDOOR AIR POLLUTION • Indoor air pollution usually is a greater threat to human health than outdoor air pollution. • According to the EPA, the four most dangerous indoor air pollutants in developed countries are: • Tobacco smoke. • Formaldehyde. • Radioactive radon-222 gas. • Very small fine and ultrafine particles.
Sick-building Syndrome • Almost one in five commercial building in the U.S. considered “sick” • Symptoms: • Dizziness • Headaches • Sore throats • Chronic fatigue • Respiratory infections • Depression
Para-dichlorobenzene Chloroform Tetrachloroethylene Formaldehyde 1, 1, 1- Trichloroethane Styrene Nitrogen Oxides Benzo-a-pyrene Particulates Tobacco Smoke Radon-222 Asbestos Carbon Monoxide Methylene Chloride Fig. 19-11, p. 453
INDOOR AIR POLLUTION • Household dust mites that feed on human skin and dust, live in materials such as bedding and furniture fabrics. • Can cause asthma attacks and allergic reactions in some people. Figure 19-12