SGCEP SCIE 1121 Environmental Science Spring 2012 Section 20531

Transcription

1 SGCEP SCIE 1121 Environmental Science Spring 2012 Section Steve Thompson: 1

2 Air pollution essentials As we learned at the beginning of the semester, the atmosphere contains many gases: N 2 (~78%), O 2 (~21%), CO 2 (~0.4%), and water vapor (from 0 to 4%). It also has several... Trace gases: including argon, ozone, helium, nitrogen oxides, and sulfur dioxides. And... Aerosols: microscopic liquid or solid particles (dust, pollen, sea salts, etc.) from land and water sources. The Industrial Revolution changed the mixture of atmospheric gases and particles. Air pollutants: substances in the atmosphere (gases and aerosols) that have harmful effects. 2

3 Pollutants Three factors determine the level of air pollution: 1. The amount of pollutants entering the air; 2. The amount of space into which the pollution is added (dispersal); 3. Mechanisms that remove pollutants from the air. Troposphere: the lower atmosphere. This is... The site and source of weather, water vapor, clouds. Pollutants are removed within hours or days. But... Pollutants in the upper troposphere can persist for many days. And, worse yet... Pollutants in the stratosphere are resistant to cleansing. Especially... Ozone-depleting chemicals (e.g. chlorine and bromine compounds). 3

4 Layers of the atmosphere 4

5 Atmospheric cleansing Natural air pollutants: volcanoes, fires, and dust storms. Plus some... Plants emit volatile organic compounds. But... Mechanisms in the biosphere remove, assimilate, and recycle these natural pollutants. In particular, hydroxyl radicals (OH): naturally occurring compounds... Oxidize many gaseous pollutants to harmless products that are brought down to land or water by precipitation. Furthermore,... Sea salts: help to nucleate raindrops that can act as a cleansing agent. These salts are... Picked up by wind flowing over oceans. And... Sunlight: breaks down organic molecules. 5

6 Hydroxyl radicals... A simplified model Remove anthropogenic pollutants from the air by oxidizing hydrocarbons, sulfides, and nitrogen oxides. The photochemical breakdown of ozone is a major source of hydroxyl radicals. 6

7 Smog Industrial smog: smoke + fog. It is... An irritating, grayish mix of soot, sulfur compounds, and water vapor. It occurs... In industrialized, cool areas that use coal. E.g.... China, India, Korea, eastern European countries. Photochemical smog: occurs in cities with huge freeway systems. It is... A brownish, irritating haze in warm, sunny areas. That... Arises during the morning traffic. Pollutants (nitrogen oxides and volatile organic compounds [VOC]) from vehicle exhaust are acted on by sunlight. 7

8 Industrial versus photochemical smog And like so many things in real life, probably most smogs are combinations of all these factors. Regardless, they can make cities look like this shot of downtown Los Angeles. 8

9 And inversions make it all much worse! Weather conditions can intensify smog. This happens because of... Temperature inversions: sometimes, warm air overlays cooler air. This... Often occurs at night and is usually short-lived. Sun heats the air and pollutants are carried away. However, cloudy weather prevents heating of the air so pollutants stay around longer. Furthermore,... Mountains can trap smog (e.g., Los Angeles and many other cities in the SouthWest U.S.A.). Long-term temperature inversions allow pollutants to build up to dangerous levels. This is opposed to the usual condition in which daytime air temperature is highest near the ground. And... Warm air rises and carries air pollution up and away. 9

10 Temperature inversion Normal situation People with breathing problems should stay inside when this happens. Excess smog causes headaches, nausea, eye/throat irritation and aggravates asthma and emphysema. At lethal levels this is called an air pollution disaster. This usually occurs... Under severe, long-lasting temperature inversions. For example... In 1952, 4,000 people died in London. 10 Inversion situation

11 Processes producing air pollution Incomplete combustion of fossil fuels and refuse... Creates gaseous and particulate products. Evaporation of volatile organic compounds (VOCs) contributes. And... Strong winds: pick up dust and other particles. Primary pollutants: direct products of combustion and evaporation. These include... Particulates, VOCs, CO, NO x, SO 2, lead, air toxics. Secondary pollutants: reactions of primary pollutants in the air produces substances like... Ozone, peroxyacetyl nitrates, and sulfuric and nitric acids. 11

12 Prime sources of anthropogenic pollutants 12

13 Primary pollutants Power plants: the major source of sulfur dioxide. Industrial plants: particulates. Transportation: carbon monoxide, nitrogen oxides. Burning fossil fuels and wastes: soot, smoke. Unburned fragments of fuel molecules: VOCs. Nitrogen oxides (NO x ): nitrogen gas is oxidized to nitric oxide (NO) under high combustion temperatures. Nitric oxide and oxygen form nitrogen dioxide (NO 2 ; photochemical smog) and nitrogen tetroxide (N 2 O 4 ). Coal also contains sulfur and heavy metals. 13

14 U.S. emissions of five primary air pollutants Fuel combustion includes fossil fuel use for producing electricity and for space heating. The two major sources of air pollution are transportation and electricity production. 14

15 Radon and secondary pollutants Radon: produced by spontaneous decay of fissionable material in rocks and soils. Escapes naturally and... Seeps into buildings through foundation cracks and basement floors. This radon... May collect in structures, though concentrations are usually quite low. However, certain regions do have problems with this. Some toxic compounds (e.g., benzene) come from transportation. However, most come from industry and small businesses. Photochemical oxidants: ozone and other reactive organic compounds formed by nitrogen oxides and VOCs. Sunlight provides the reaction s energy. Ozone concentrations in preindustrial times: ppb. Unpolluted, summer air in North America: ppb. Polluted air: 150 ppb or more (very unhealthy). Ambient U.S. ozone levels decreased 20% from ; But only a few percent in the 2000s. 15

16 Ozone formation Nitrogen dioxide absorbs light energy and splits... Forming nitric oxide and atomic oxygen. The oxygen combines with oxygen gas, forming ozone. Ozone and nitric oxide usually react to form NO 2 and O 2, which means there is... No accumulation of ozone. However,... When VOCs are present, nitric oxide reacts with them and... Creates highly reactive, damaging peroxyacetyl nitrates (PANs). Oxidized PANs produce aldehydes and ketones. And ozone accumulates. Bummer. 16

17 Formation of ozone and other photochemical oxidants 17

18 Ozone in the atmosphere 18 Ozone good and bad! Stratospheric ozone (good ozone) protects the Earth from harmful ultraviolet radiation. Ozone is formed in the stratosphere: UV radiation splits O2 molecules into free oxygen (O): O2 + UVB O + O Some O combines with O2 to form ozone (O3): O + O2 O3 However, chlorofluorocarbons (CFCs) destroy the ozone layer. Used in refrigerators, air conditioners, production of foams, aerosol cans, etc. The ozone shield: stratospheric ozone absorbs most (99%) UV radiation. The remaining 1% UVB radiation causes skin cancer, and damages crops and other life forms.

19 Stratospheric ozone Worldwide stratospheric ozone losses of 3% 6% have occurred from 2002 to These sort of ozone losses from the 1980s will have caused 12 million people in the U.S. to develop skin cancer! 19 In 1985, scientists noticed a hole (serious thinning) in the stratospheric ozone layer over the South Pole. Ozone levels were 50% lower than normal in an area the size of the U.SA. Turns out it is related to CFCs the chlorines react with the ozone in a catalytic fashion they don t get used up, but the ozone goes away! And it s seasonal, being way worse in the Spring (our Autumn in Antarctica) due to the polar vortex. Ozone-poor air has spread all over the Southern Hemisphere. For example... Queensland, Australia: two out of three are expected to develop skin cancer! The Arctic has 25% depletion, but no ozone hole.

20 Ozone loss and the size of the hole 20

21 Production and presence of ozonedepleting substances in the atmosphere CFCs in blue, their replacement HCFCs in green. It is obviously working, but will take many, many years. 21

22 Acid precipitation and deposition Sulfuric acids and nitric acids are the... Products of sulfur dioxide and nitrogen oxides reacting with atmospheric moisture and oxidants (e.g., hydroxyl radicals). And are... The acids in acid rain (acid deposition). Acid precipitation: any precipitation (rain, fog, mist, snow) more acidic than usual. Acid deposition: acid precipitation plus dryparticle fallout. This phenomenon... Affects broad areas of North America, Europe and other industrialized nations. The... Precipitation is 10 1,000 times more acidic than usual in these areas. 22

23 Acid deposition 23

24 Extent and potency of acid precipitation Rainfall is normally slightly acidic (ph = 5.6). Acid precipitation: any precipitation with a ph < 5.5. Acid precipitation is now the norm over most of the industrialized world. Eastern North America: rain and snow ph = 4.6. This is due to polluted air from the Midwest and industrial Canada. And it... Can be as low as ph = 3.0. Mountain forests east of Los Angeles have a ph = 2.8. This is... 1,000 times more acidic than usual! 24

25 Acid deposition in eastern North America 25

26 Natural versus anthropogenic sources of acid deposition Sulfuric acid (H 2 SO 4 ) and nitric acid (HNO 3 ) occur in a ratio of 2 to 1; But west U.S. and Canada have more nitric acid. Natural sources of sulfur dioxide: million tons/year come from volcanoes, hot springs, sea spray, and microbial processes. And... Natural sources of nitrogen oxides: million tons/year come from lightning, wildfire, and microbial processes. However, the products of burning fuels are oxidized by hydroxyl radicals in the troposphere forming extra sulfuric and nitric acid. Sulfur dioxide: million tons/year mainly from coal combustion. Nitrogen oxides: million tons/year mainly from transportation. Anthropogenic sources: concentrated in industrialized areas. Emissions have increased 4x since Old U.S. coal-burning power plants are reducing emissions; and... Deposition has decreased around 35% in the past 15 years. 26

27 Eastern U.S. coal-burning power plants 27

28 Impact of all air pollutants We are exposed to a mixture of pollutants... That vary over time and place. Plants may become so stressed from pollution that they are vulnerable to drought or insects pests. Human health: every single one of the primary and secondary air pollutants is a threat to human health. Acute exposure can be life threatening. Versus... Chronic exposure: long-term exposure can cause gradual deterioration and premature mortality. Some pollutants can even contribute to lung cancer. Sulfur dioxide: leads to bronchitis (inflammation of the bronchi). Ozone: leads to inflammation and scarring of the lungs. Carbon monoxide: reduces the oxygen-carrying capacity of the blood and leads to heart disease. Nitrogen oxides: impair lung function and affect the immune system. Particulate matter: respiratory and cardiovascular pathologies. 28

29 A biggy is COPD and asthma. Chronic obstructive pulmonary disease (COPD) is... A slowly progressive lung disease that makes it hard to breathe. It is the 4th leading cause of death in the U.S. and affects 18 million people here. Furthermore, it... Affects 10% of adults over 40 worldwide! Largely it is caused by... Smoking tobacco, but it is also associated with burning biomass fuels. It involves three diseases: emphysema (destruction of the lung alveoli), bronchitis, and asthma. Those people... Most sensitive to air pollution are small children, asthmatics, those with chronic pulmonary or heart disease, and the elderly. A vicious circle! Asthma is an immune disorder characterized by... Impaired breathing caused by constricted airways. It is triggered by allergens (dust, mites, mold, pet dander). But... Is also triggered by pollution (ozone, particulates, and SO 2 ). It... Causes 500,000 hospitalizations/year, with million visits to emergency departments. Furthermore,... In the last decade, U.S. asthma has doubled (to 23 million). 29

30 Strong evidence support Studies of thousands of adults show strong evidence of harm caused by fine particulates and sulfur pollution. This includes... Asthma, chronic bronchitis, cardiovascular problems, etc. Higher concentrations of fine particles correlate with increased mortality from cardiopulmonary disease and lung cancer. Meeting EPA standards would save $28 billion/year in avoided health costs, missed work, premature deaths, etc. in CA alone! Air pollution can kill people already suffering from heart or respiratory diseases. Moderate air pollution can change cardiac rhythms in people with heart disease triggering fatal heart attacks. Furthermore, many air pollutants are known carcinogens: Diesel: a likely human carcinogen; Benzene: clearly correlated with cancer; it is found... In motor fuels, solvents, explosives, smoke, medicines, and is... Linked to leukemia, blood disorders, damaged immunity. 30

31 The environment also suffers. Plants are more sensitive than humans to air pollution. Sulfur dioxide from smelters and power plants killed large areas of vegetation. Ozone damages crops, orchards, and forests. Crops vary in their susceptibility to ozone. Soybeans, corn, wheat are damaged at ambient ozone levels. Countries lose billions of dollars/year in lower yields. Damage to trees and wild plants may exceed crop damage. E.g. Ponderosa and Jeffrey pines in California were damaged by ozone from the San Francisco-Oakland area. Trees weakened by ozone were susceptible to pine beetles. Tree damage starts at 40 ppb ozone and intensifies with higher levels California and the Appalachians have levels = 60 ppb. Resulting in 30% 50% less stem growth. 31

32 Ozone impact on crop yields 32

33 Effects on materials and human structures Particulates turn walls, windows, and surfaces dingy. Oxidation by ozone: deteriorates rubber. Sulfur dioxide and sulfur or nitrogen oxides corrode metal. And weather and deteriorate stonework. It costs hundreds of millions of dollars/year to clean or replace damaged materials. Historic statues and carvings are irreplaceable. Limestone and marble are used on buildings and monuments (artifacts). Acid deposition rapidly erodes these structures. Hundred- or thousand-year-old structures are crumbling. It costs billions of dollars/year to replace or repair structures. Acid deposits cross national boundaries 33

34 Acid deposition: aquatic ecosystems Acid deposition s impacts on ecosystems were noted 45 years ago. Impact on aquatic ecosystems: an environment s ph affects enzymes, hormones, and other proteins. Organisms can regulate their internal ph within limits. A low ph overwhelms regulatory mechanisms, killing or weakening the organism. Ponds, lakes, and streams have a natural ph of 6 8. Eggs, sperm, and developing young are very sensitive to small changes in ph. A ph below 5 kills organisms or impairs their reproduction. Acid precipitation can leach heavy metals from soil, which are absorbed by organisms and are highly toxic. Mercury accumulates in fish in acidic lakes. Ontario, Canada lost fish in 1,200 lakes. 346 lakes in the Adirondacks in New York lost fish. The clear, blue lakes look healthy but contain only acid-loving moss growing on the bottom and other acidophilic organisms. 34

35 Impacts on forests Forests from Vermont to California died off during the 1980s. For example million acres in New England died! Trees lose needles and become more susceptible to frost and other environmental stresses (pests); Sugar maples suffer 20% 80% losses. Acid precipitation adds sulfur and nitrogen to soil. Stimulating tree growth.... But leaching out calcium and magnesium (buffers). Toxic aluminum oxides are also leached from the soil. Tree growth is subsequently reduced. Adding lime to the soil helps to restore tree health. 35

36 Costs and benefits We have air pollution because we want the goods and services that generate it. Benefits may be essential or trivial;... But we want them if we can afford them. Air pollution does not have to get worse;... But remedies come at an economic cost. Critics of control see lost opportunities for growth but disregard the costs avoided (e.g., improved health). For example, a cost-benefit analysis of the Acid Rain Reduction Program estimated that... For 2010, benefits = $122 billion, costs = $3 billion. It s a no-brainer! 36

37 Field news the good side of the story Air quality has improved, especially SO 2 and sulfate reduction, along with health benefits. Regulations and cooperation has... Reduced acid deposition, achieved freshwater recovery in some acidified streams and lakes, and improved many forest conditions. But nitrogen deposition is still a problem. Plus... Sulfur has built up in the soils worldwide. Recovery depends on further reductions in sulfur and nitrogen. Regardless, check out the graphs for the good news... 37

38 SO 2 emissions under the Acid Rain Reduction Program 38

39 Clean Air Act impacts 39

40 Comparison of growth vs. emissions 40

41 Final thoughts The ozone story is a remarkable episode in human history. The world has shown that it can respond collectively and effectively to a clearly perceived threat. The scientific community played a crucial role in... Alerting the world; and... Researching the threat. Skeptics stressed uncertainties but scientific consensus convinced politicians to act! Let s just hope science can work in so many other ways to convince the public and the politicians that action needs to be undertaken. Next we ll look at water pollution. 41