Chapter 24: Air Pollution A Brief History of Air Pollution • The atmosphere has long been a sink for waste disposal. • Long history of recognition of the existence of atmospheric pollutants – Natural photochemical smog recognized in 1550 – Acid rain first described in 17th century – Word smog introduced in 1905 • Mixture of smoke and fog A Brief History of Air Pollution • Two events sparked research on air pollution and regulations to control air quality. – Donora fog in 1948 – London smog event in 1952 – Both cause by pollutants being trapped by weather events. Both killed numerous people. – Could happen again in cities like Beijing or Mexico City Stationary Source of Air Pollution • Stationary sources are those that have a relatively fixed location. – Point sources emit pollutants from one or more controllable sites. – Fugitive sources generate air pollutants from open areas exposed to wind processes. – Area sources are well defined areas within which are several sources of air pollutants. Point source Fugitive source Mobile Source of Air Pollution • Mobile source of air pollutants move from place to place while emitting pollutants. – Automobiles, trucks, buses, aircraft, ships, and trains. General Effects of Air Pollution • Affects many aspects of our environment – – – – – – – Visual qualities Vegetation Animals Soil Water quality Natural and artificial structures Human health General Effects of Air Pollution • Significant factor in human death rate for many large cities – Athens, Greece- # of deaths higher on bad air quality days – Hungary- 1 in 17 deaths contributed to air pollution – US- 300,000 deaths/year, health cost $50 billion – China- health cost $50 - $100 billion General Effects of Air Pollution • Affect human health in several ways – Toxic poisoning, cancer, birth defects, eye irritation, and irritation of respiratory system. – Increased susceptibility to viral infections, causing pneumonia and bronchitis. – Increased susceptibility to heart disease. – Aggravation of chronic diseases, such as asthma and emphysema. General Effects of Air Pollution • Many air pollutants have synergistic effects – Do greater damage to the lungs than a combination of the two pollutants would be expected to do based on their separate effects. Air Pollutants • 200 air pollutants recognized and assessed by US EP and listed in Clean Water Act – Six called critical pollutants Primary and Secondary Pollutants • Major air pollutants occur either in gaseous forms or as particulate matter. • Classified as primary or secondary – Primary pollutants- emitted directly into the air – Secondary pollutants- produced through reactions between primary pollutants and normal atmospheric compounds. Primary and Secondary Pollutants • In addition to human sources, our atmosphere contains many pollutants of natural origin. – Release of sulfur dioxide from volcanic eruptions. – Release of hydrogen sulfide from geysers and hot springs and from biological decay in bogs and marshes. – Release of ozone in the lower atmosphere as a result of unstable meteorological conditions. – Emission of a variety of particles from wildfires and – windstorms. – Natural hydrocarbon seeps. Criteria Pollutants • There are six criteria pollutants – – – – – – Sulfur dioxide Nitrogen oxides Carbon monoxide Ozone Particulates Lead Sulfur Dioxide • SO2 – Colorless odorless gas – Once emitted can be converted to sulfateSO4 – Removed from atmosphere by wet or dry deposition – Major human sources; coal power plants, industrial processes Sulfur Dioxide • Adverse effects depend on dose and concentration present – Injury or death to animals and plants – Corrosion of paint and metals – Important precursor to acid rain Nitrogen Oxides • Occur in many forms in the atmosphere but largely emitted in two forms: – Nitric oxide- NO – Nitrogen dioxide- NO2 • A yellow-brown to reddish-brown gas • May be converted to NO32- – Both subject to emissions regulation and contribute to smog – NO2 major contributor to acid rain Nitrogen Oxides • Nearly all NO2 emitted from human sources – Automobiles and power plants that burn fossil fuels • Environmental effects – Irritate eyes and mucous membranes – Suppress plant growth • However when convert to nitrate may promote plant growth Carbon Monoxide • CO is a colorless, odorless gas – Even at low concentrations is extremely toxic to humans • Binds to hemoglobin in blood. – 90% of CO in atmosphere comes from natural sources – 10% comes from fires, cars, and incomplete burning of organic compounds Ozone and Other Photochemical Oxidants • Photochemical oxidants result from atmospheric interactions of nitrogen dioxide and sunlight. – Most common is ozone- O3 – Colorless gas w/ slightly sweet odor – Very active chemically, oxidizes or burns • Beneficial in the upper atmosphere Ozone and Other Photochemical Oxidants • Because ozone is a secondary pollutant it is difficult to regulate. – Health standards often exceeded in urban areas • Effects include – Kills leaf tissue at high concentration – Damage eyes and respiratory system – Even young, healthy people may have breathing difficulty on polluted days Particulate Matter • PM10 is made up of particles less than 10μm in diameter – Present everywhere but high concentrations and/or specific types dangerous – Much particulate matter easily visible as smoke, soot, or dust – Includes airborne asbestos and heavy metals Particulate Matter • Of particular concern are very fine pollutants – PM 2.5- less than 2.5 μm in diameter – Easily inhaled into the lungs, then absorbed into the bloodstream – Ultrafine particles- <0.18 μm released by automobiles. • Related to heart disease Particulate Matter • When measured often referred to as total suspended particles (TSPs) – Tend to be highest in large cities in developing countries Particulate Matter • Recent studies estimate that 2 to 9% of human mortality in cites is associated w/ PM – Linked to both lung cancer and bronchitis – Especially hazardous to elderly and those w/ asthma • Dust can be deposited on plants – Interferes w/ absorption of CO2 and O2 and transpiration Particulate Matter • Block sunlight and may cause climate change. • Global dimming – Gradual reduction in the solar energy that reaches the surface of Earth – Cools the atmosphere – Lessens global warming Lead • Lead is constituent of auto batteries and used to be added to gasoline. – Lead in gas emitted into air w/ exhaust – Spread widely around world in soils and water along roadways – Once in soil can enter the food chain – Lead now removed from gas in US, CAN, EU • 98% reduction in emissions since 1970s Air Toxics • Among pollutants that are known or suspected to cause cancer or other serious health problems. – Associated w/ long-term and short-term exposures – Gases, metals, and organic chemicals that are emitted in relatively small volumes – Cause respiratory, neurological, reproductive, or immune diseases Air Toxics • Standards have been set for more than 150 air toxics – E.g. hydrogen sulfide, hydrogen fluoride, chlorine gases, benzene, methanol, ammonia – EPA estimates that the average risk for cancer from exposure to air toxics is about 1 in 21,000 Hydrogen sulfide • Highly toxic corrosive gas easily identified by its rotten egg odor. • Produced from – Natural sources such as geysers, swamps, and bogs – Human sources such as industrial plants that produce petroleum or that smelt metals. • Effects of hydrogen sulfide include – Functional damage to plants – Health problems ranging from toxicity to death for humans and other animals. Hydrogen Fluoride • Extremely toxic gaseous pollutant • Released by some industrial activities – Such as production of aluminum, coal gasification, and burning of coal in power plants. • Even a small concentration (as low as 1 ppb) of HF may cause problems for plants and animals. – Potentially dangerous to grazing animals because forage plants can become toxic when exposed to this gas. Methyl Isocyanate • An ingredient of a common pesticide – known in the United States as Sevin. • Colorless gas • Causes severe irritation (burns on contact) to eyes, nose, throat, and lungs. – Breathing the gas in concentrations of only a few ppm causes violent coughing, swelling of the lungs, bleeding, and death. – Less exposure can cause a variety of problems, including loss of sight. Volatile Organic Compounds • Variety of organic compounds used as solvents in industrial processes – Dry cleaning, degreasing, and graphic arts. • Hydrocarbons – Comprise one group of VOCs. – Thousands of hydrocarbon compounds exist, including natural gas, or methane (CH4); butane (C4H10); and propane (C3H8). Volatile Organic Compounds • Some VOCs react w/ sunlight to produce photochemical smog • Globally 15% of hydrocarbons emissions are anthropogenic – In the US 50% – Primary human source automobiles Benzene • Additive in gasoline and an important industrial solvent. • Produced when gasoline and coal undergo incomplete combustion. – Also component of cigarette smoke – Major environmental source on and off road vehicles Arcolein • A volatile hydrocarbon that is extremely irritating to nose, eyes, and respiratory system. • Produced from – Manufacturing processes that involve combustion of petroleum fuels – Component of cigarette smoke Variability of Air Pollution • Problems vary in different regions of the country and the world. – LA pollution mainly from mobile sources – Ohio and Great Lakes point sources • Also varies w/ time of year – Smog a problem in summer when there is lots of sunshine – Particulates a problem in dry months Las Vegas: Particulates • Particulates a problem in arid regions – Where little vegetation is present and wind can easily pick up and transport fine dust. – Brown haze over Las Vegas partly due to naturally occurring PM 10 – 60% of the dust comes from new construction sites, dirt roads, and vacant land. Haze From Afar • Air quality concerns are not restricted to urban areas. – North slope of AK has an air pollution problem that originates from sources in EE and Eurasia. – Transported by the jet stream. – Significant as we try to understand global air pollution. Urban Air Pollution • Whether air pollution develops depends on topography and meteorological conditions – Determine the rate at which pollutants are transported away and converted to harmless compounds. Influences of Meteorology and Topography • Meteorological conditions determine whether air pollution is a nuisance or major health problem. • Primary adverse effect – Damage to green plants and aggravation of chronic disease – Usually low-level over long period of time – However major disaster have occurred Influences of Meteorology and Topography • In the lower atmosphere, restricted circulation associated w/ inversion layers may lead to pollution events. • Atmospheric inversion– Occurs when warmer air is found above cooler air Occurs primarily in summer and fall. Occurs when cloud cover associated w/ stagnant air Influences of Meteorology and Topography • Cities situated in a valley or topographic bowl are more susceptible to smog problems than cities in open plains. • Surrounding mountains and inversions prevent pollutants from being transported by wind or weather systems. – E.g. Los Angeles Potential for Urban Air Pollution • Determined by the following factors: – 1. The rate of emission of pollutants per unit area. – 2. The downwind distance that a mass of air moves through an urban area. – 3. The average speed of the wind. – 4. The elevation to which potential pollutants can be thoroughly mixed by naturally moving air in the lower atmosphere. Potential for Urban Air Pollution • Concentration of pollutants in the air is directly proportional to the first two factors. – As either emission rate or down wind travel distance increase, so will the concentration of pollutants • City air pollution decreases w/ increases in third and forth factors. – The stronger the wind and the higher the mixing layer, the lower the pollution. Smog • Term first used in 1905 as mixture of smoke and fog that produced unhealthy air. • Two major types – Photochemical smog (LA type smog or brown air) – Sulfurous smog (London type smog, gray air, or industrial smog) Smog • Photochemical smog reaction involves sunlight, nitric oxides and VOCs – Directly related to automobile use • Sulfurous smog is produced by the burning of coal or oil at large power plants. Future Trends for Urban Areas • The optimistic view – Air quality will continue to improve – Because we know so much about the sources of air pollution and have developed effective ways to reduce it. • The pessimistic view – In spite of this knowledge, population pressures and economics will dictate what happens in many parts of the world, – The result will be poorer air quality in many locations. Future Trends for Urban Areas; The United States • LA is a good area to look at for strategies for pollution abatement. • Air quality plan involving the entire urban region includes the following features: – Strategies to discourage automobile use and reduce the number of cars. – Stricter emission controls for automobiles. – A requirement for a certain number of zero-pollutant automobiles (electric cars) and hybrid cars with fuel cell and gasoline engines. Future Trends for Urban Areas; The United States – A requirement for more gasoline to be reformulated to burn cleaner. – Improvements in public transportation and incentives for people to use it. – Mandatory carpooling. – Increased controls on industrial and household activities known to contribute to air pollution. Future Trends for Urban Areas; The United States • Have focused on LA because the air quality is so poor for a significant portion of the year. • However, many large and not so large US cities have poor air quality – 30 days per year of unhealthy air resulting from ozone pollution. Future Trends for Urban Areas; Developing Countries • Less developed countries w/ growing populations are susceptible to air pollution – Don’t have the financial base necessary to fight air pollution • E.g. Mexico City – – – – 25 million people 50,000 buses, millions of cars, LPG leaks In a natural basin w/ mountains surrounding it Perfect situation for severe air pollution problem Future Trends for Urban Areas; Developing Countries • Attempts to reduce air pollution – Shutting down oil refinery – Ordering industrial plants to relocate • Air pollution however will continue to be a problem if unable to control vehicle use and LPG leaks. Pollution Control • The most reasonable strategies for control have been to reduce, collect, capture, or retain the pollutants before they enter the atmosphere. – Reduction of emissions through energy efficiency and conservation measures is preferred. Pollution Control: Particulates • Particulates emitted from fugitive, point or area stationary sources are much easier to control. • Point and area sources can be controlled by – Settling chambers or collectors which cause particulates to settle out • Fugitive sources – Protecting open areas, controlling dust, reducing effects of wind Pollution Control: Automobiles • Control of pollutants such as carbon monoxide, nitrogen oxides, and hydrocarbons is best achieved through pollution control for automobiles. – Nitrogen oxides controlled by recirculating exhaust gas – CO and hydrocarbons reduced by catalytic converter Pollution Control: Automobiles • Automobile emission regulations plan in US has not been effective – Pollutants may be low when car is new – But many people do not maintain them properly – Suggested that effluent fees replace emission controls – Other strategies reduce the number or type of cars Pollution Control: Sulfur Dioxide • Can be reduced through abatement measures performed before, during, or after combustion. • Cleaner coal technology available but makes fuel more expensive. • Switch to low-sulfur coal – But transportation is an issue Pollution Control: Sulfur Dioxide • Washing it to remove sulfur – Iron sulfide settles out – Ineffective for removing organic sulfur • Coal gasification – Converts coal to gas in order to remove sulfur – Gas obtained is clean Pollution Control: Sulfur Dioxide • Emissions from power plants can be reduced by removing the oxides from the gases in the stack – – – – – Scrubbing (flue gas desulfurization) Occurs after coal is burned Gases treated w/ a slurry of lime or limestone Reacts to form calcium sulfite Can then be process into building materials Clean Air Act Amendments of 1990 • Comprehensive regulations enacted by the U.S. Congress that address acid rain, toxic emissions, ozone depletion, and automobile exhaust. • Buying and selling of sulfur dioxide emissions • One step back occurred in 2003 when the president and EPA allowed companies to upgrade w/o new pollution controls. Clean Air Act Amendments of 1990 • Also calls for control of • Nitrogen dioxides – Reduced by 10 million tons • Toxins – Especially those causing cancer • Ozone depletion in the stratosphere – End production of all CFCs Ambient Air Quality Standards • Important because they are tied to emission standards that attempt to control air pollution. • Tougher standards set for ozone and PM 2.5 – When challenged in court justices help that the EPA’s responsibility is to consider benefits to health not financial costs. Air Quality Index • AQI is used to describe air pollution on a given day. • AQI is determined from measurements of the concentration of five major pollutants: – Particulate matter, sulfur dioxide, carbon monoxide, ozone, and nitrogen dioxide. Air Quality Index • An AQI value of greater than 100 is unhealthy. • Air pollution alert is issued if the AQI exceeds 200. • Air pollution warning is issued if the AQI exceeds 300, hazardous to all people. • If the AQI exceeds 400, an air pollution emergency is declared, and people are requested to remain indoors and minimize physical exertion. Cost of Air Pollution Control • Cost for incremental control in fossil fuelburning may be a few hundred dollars per additional ton of particulates removed. • For aluminum plant, may be several thousand per ton. • Also, a point is reached at which the cost of incremental control is very high in relation to additions benefits. Cost of Air Pollution Control • Economic analysis of air pollution includes many variables, some of which are hard to quantify. We do know the following: – W/ increasing air pollution controls, the capital cost for technology to control air pollution increases. – As the controls for air pollution increase, the loss from pollution damages decreases. – The total cost of air pollution is the cost of pollution control plus the environmental damages of the pollution. Ozone Depletion • Ozone (O3) – Triatomic form of oxygen in which three atoms of oxygen are bonded. – Strong oxidant and chemically reacts with many materials in the atmosphere. – In the lower atmosphere, ozone is a pollutant. – Highest concentration of ozone in the stratosphere Ultraviolet Radiation and Ozone • Ozone layer in the stratosphere called the ozone shield – Absorbs most of the potentially hazardous ultraviolet radiation from the sun. • Ultraviolet radiation consists of wavelengths between 0.1 and 0.4 μm – Ultraviolet A (UVA) – Ultraviolet B (UVB) – Ultraviolet C (UVC). Ultraviolet Radiation and Ozone • Ultraviolet C (UVC) – Shortest wavelength and most energetic of the types of ultraviolet radiation. – Sufficient energy to break down diatomic oxygen (O2) into two oxygen atoms. – Each of these oxygen atoms may combine with an O2 molecule to create ozone. • UVC strongly absorbed in the stratosphere, and negligible amounts reach the Earth’s surface. Ultraviolet Radiation and Ozone • Ultraviolet A (UVA) – Longest wavelength – Least energy of the three types of ultraviolet radiation. – UVA can cause some damage to living cells – Not affected by stratospheric ozone, and is transmitted to the Earth’s surface Ultraviolet Radiation and Ozone • Ultraviolet B (UVB) – Energetic and strongly absorbed by stratospheric ozone – Ozone is the only known gas that absorbs UVB. – Depletion of ozone in the stratosphere results in an increase in the UVB that reaches the surface of the Earth. Ultraviolet Radiation and Ozone • Approximately 99% of all ultraviolet solar radiation (all UVC and most UVB) is absorbed by the ozone layer. – Natural service function – Protects us from the potentially harmful effects of ultraviolet radiation. Measurement of Stratospheric Ozone • First measured in 1920s using Dobson ultraviolet spectrometer. – Dobson unit (DU)- 1DU = 1 ppb O3 – Now have measurements from all over the world for 30 years • Ground based measurements first identified ozone depletion over the Antarctic. – Concentrations have been decreasing since the mid1970s – “Ozone hole” Ozone Depletion and CFCs • Hypothesis that ozone in the stratosphere is being depleted by CFCs – First suggested in 1974 by Molina and Rowland. – Based on physical and chemical properties of CFCs and knowledge about atmospheric conditions. – Vigorously debated by scientists, companies producing CFCs, and other interested parties. Ozone Depletion and CFCs • The major features of the hypothesis: – CFCs emitted in the lower atmosphere are extremely stable. Unreactive in the and therefore have a very long residence time (about 100 years). – CFCs eventually wander upward and enter the stratosphere. – Once above the stratospheric ozone, they may be destroyed by UV radiation, releasing chlorine, a highly reactive atom. Ozone Depletion and CFCs – The chlorine released then depletes the ozone. – Depletion increases the amount of UVB radiation that reaches Earth’s surface. – UVB is a cause of human skin cancers and is also thought to be harmful to the human immune system. Emissions and Uses of Ozone Depleting Chemicals • CFCs have been used – As aerosol propellants in spray cans – Working gas in refrigeration and AC – Production of Styrofoam • No longer used in spray cans but use has increased in refrigerants. Simplified Stratospheric Chlorine Chemistry • CFCs are – transparent to sunlight, – essentially insoluble – Non-reactive in the oxygen-rich lower atmosphere • When CFCs reach the stratosphere, reactions do occur. • UVC splits up the CFC releasing chlorine, the following two reactions can take place: Cl + O3 → ClO + O2 ClO + O → Cl + O2 Simplified Stratospheric Chlorine Chemistry • This series of reactions is what is known as a catalytic chain reaction. – Chlorine is not removed – Reappears in the second reaction – Repeated over and over • Process considerably more complex • Chain can be interrupted and Cl stored in other reactions The Antarctic Ozone Hole • Since 1958 ozone depletion has been observed in the Antarctic every Oct. – Thickness decreasing and geographic area increasing Polar Stratospheric Clouds • Form during the polar winter (polar night) – Antarctic air mass isolated from the rest of the atmosphere – Air circulates about the pole in Antarctic polar vortex. – Forms as the isolated air mass cools, condenses, and descends. Polar Stratospheric Clouds • Type I polar stratospheric clouds – When air mass reach a temp between 195 K and 190 K, small sulfuric acid particles are frozen and serve as seed particles for nitric acid (HNO3). • Type II polar stratospheric clouds – If temperatures drop below 190 K water vapor condenses around Type I cloud particles Polar Stratospheric Clouds • During the formation nearly all the nitrogen oxides held in clouds – Facilitates ozone depleting reactions – When spring comes and sun returns it breaks apart Cl2 – Chlorine can not be sequestered to form chlorine nitrate, one of its carbon sinks. An Arctic Ozone Hole? • Polar vortex also forms over the North Pole – Weaker and does not last as long as Antarctic – Ozone depletion does occur at the NP – Major concern is ozone-deficient air moving southward over population centers. Tropical and Midlatitude Ozone Depletion • Evidence suggests an increase in ozone depletion at midlatitudes over areas including the US and Europe. • We know the most about ozone depletion in polar regions (particularly Antarctica), but depletion of ozone is a global concern. The Future of Ozone Depletion • If the manufacture, use, and emission of all ozone-depleting chemicals were to stop today, the problem would not go away, – millions of metric tons of those chemicals are now in the lower atmosphere, working their way up to the stratosphere. • Several CFCs have atmospheric lifetimes of 75 to 140 years. Environmental Effects • Several serious potential environmental effects – Damage to food chain on land and in oceans (loss of primary production ) – Damage to human health (skin cancers, cataracts, and suppression of immune system) • UV Index measure of UV radiation on a given day Environmental Effects • Reduce the risk of skin cancer and other skin damage from UV exposure by: – Limit exposure to the sun between the hours of 10 A.M.and 4 P.M. – When possible, remain in the shade. – Use a sunscreen with an SPF of at least 30. – Wear a wide-brimmed hat and, where possible, tightly woven full-length clothing. – Wear UV-protective sunglasses. – Avoid tanning salons and sunlamps. – Consult the UV Index before going out Management Issues • The Montreal Protocol – Outlined a plan for the eventual reduction of global emissions of CFCs to 50% of 1986 emissions – Elimination of the production of CFCs by 1999 – Assessment of the protocol suggest that CFCs will return to pre-1980 levels by 2050 Management Issues • Substitutes for CFCs – hydrofluorocarbons (HFCs) and • Do not contain chlorine. However, fluorine atoms participate in reactions similar to those of chlorine but approximately 1,000 times less efficient in those reactions – hydrochlorofluorocarbons (HCFCs). • Contain an atom of hydrogen in place of a chlorine atom. Can be broken down in the lower atmosphere. However, cause ozone depletion if they do reach the stratosphere before being broken down. Management Issues • Short-term Adaptation to Ozone Depletion – Given the nature of problem and the atmospheric lifetimes of the chemicals that produce the depletion – people will be learning to live with higher levels of exposure to ultraviolet radiation. • In the long term, achievement of sustainability w/ respect to stratospheric ozone will require management of human-produced ozone-depleting chemicals.