ENVE203 Environmental Engineering Ecology (Dec 31, 2012)

Transcription

1 ENVE203 Environmental Engineering Ecology (Dec 31, 2012) Elif Soyer Air Pollution

2 The Atmosphere as a Resource A gaseous envelope surrounding Earth N % O % Ar 0.93% CO % Other gases & particles including pollutants occur in much smaller concentrations

3 The Atmosphere as a Resource Two important gases most important to humans and other organisms are CO 2 & O 2 Photosynthesis Cellular respiration

4 The Atmosphere as a Resource The atmosphere performs additional ecosystem services Blocking Earth s surface from much of the UV radiation coming from the sun Moderating the climate Redistributing water in the hydrologic cycle

5 Types & Sources of Air Pollution Air pollution: Various chemicals added to the atmosphere by natural events or human activities in high enough concentrations to be harmful

6 Types & Sources of Air Pollution Gases Liquids Solids Present in the atmosphere in high enough levels to harm humans, other organisms, or materials

7 Natural sources Air pollution as when lightening causes a forest fire or a volcano erupts The most important source is human activities releasing many kinds of substances into the atmosphere Some of these are harmful when they precipitate & settle on land & surface waters Other substances are harmful because they change the chemistry of the atmosphere

8 7 most important types of air pollutants Particulate matter (PM) Nitrogen oxides (NOx) Sulfur oxides (SOx) Carbon oxides (COx) Hydrocarbons (HC) Ozone (O 3 ) Air toxics

9 Major Air Pollutants

10 1. Primary air pollutants 2. Secondary air pollutants Air Pollutants

11 Primary air pollutant: Air Pollutants A harmful substance, such as carbon monoxide, that is emitted directly into the atmosphere Carbon oxides, nitrogen oxides, sulfur oxides, particulate matter, and hydrocarbons

12 Secondary air pollutant: Air Pollutants A harmful substance formed in the atmosphere when a primary air pollutant reacts with substances normally found in the atmosphere or with other air pollutants Ozone & sulfur trioxide are formed by chemical reactions that take place in the atmosphere

13 Particulate Matter (PM) Consists of thousands of different solid & liquid particles suspended in the atmosphere Soil particles, soot, lead, asbestos, sea salt, & sulfuric acid droplets Solid particulate matter- generally referred to as dust Liquid suspensions- commonly called mist

14 Particulate matter (PM) Reduces visibility by scattering & absorbing sunlight Urban areas receive less sunlight than rural areas Particulate matter corrodes metals, erodes buildings & sculptures when the air is humid, and soils clothing

15 Particulate matter can be dangerous 1. It may contain materials- such as heavy metals, asbestos, or organic chemicals- that have toxic or carcinogenic effects 2. Extremely small particles, even if not toxic, can get lodged deep in the lungs

16 Microscopic particles PM-10 Particulate matter less than 10 µm in diameter PM-2.5 Particulate matter less than 2.5 µm in diameter

17 Lead A soft metal that is used in industrial & chemical processes Airborne lead can be a problem both when it is inhaled & when it settles- in water & on surfaces including foods Acute poisoning rarely results from outdoor exposure Chronic effects can include Permanently reduced cognitive ability, Behavioral problems Slowed growth Hearing problems Headaches

18 Nitrogen oxides (NOx) Gases produced by the chemical interactions between atmospheric nitrogen & oxygen when a source of energy, such as combustion of fuels, produces high temperatures Collectively known as NOx Nitric oxide (NO) Nitrogen dioxide (NO 2 ) Nitrous oxide (N 2 O)

19 Nitrogen oxides (NOx) Inhibit plant growth When breathed, aggravate health problems such as asthma NOx are involved in the production of photochemical smog & acid deposition (cause metals to corrode & textiles to fade & deteriorate) N 2 O traps heat in the atmosphere: a greenhouse gas. Causes global warming

20 Sulfur Oxides (SOx) Gases produced by the chemical interactions between sulfur & oxygen A major sulfur oxide emitted as a primary air pollutant: SO 2 (sulfur dioxide) a colorless, nonflammable gas with strong, irritating odor Another major sulfur oxide: sulfur trioxide (SO 3 ) a secondary air pollutant that forms when sulfur dioxide reacts with water to form another secondary air pollutant, sulfuric acid

21 Sulfur Oxides cause Acid deposition Corrosion of metals Damage stone & other materials Sulfuric acid & sulfate salts produced in the atmosphere form sulfur oxides damage plants & irritate the respiratory tracts of humans & other animals

22 Carbon Oxides (COx) Gases carbon monoxide (CO) & carbon dioxide (CO 2 ) CO a colorless, odorless, and tasteless gas produced in the largest quantities of any atmospheric pollutant except CO 2 CO is poisonous & interferes with the blood s ability to transport oxygen CO 2 also colorless, odorless, and tasteless gas CO 2 buildup in the atmosphere: global climate change

23 Hydrocarbons (HC) Diverse group of organic compounds that contain only hydrogen & carbon Simplest HC is methane (CH 4 ) principle component of natural gas Small HC molecules are gaseous at room temperature All HC except CH 4 are important in the production of photochemical smog CH 4 is a potent greenhouse gas linked to global climate change

24 Ozone (O 3 ) A pale blue gas that is both a pollutant in the lower atmosphere (troposphere) and an essential component that screens out UV irradiation in the upper atmosphere (stratosphere)

25 Ozone in the stratosphere Oxygen reacts with UV radiation coming from the sun to form ozone Stratospheric ozone prevents much of the solar UV radiation from penetrating to Earth s surface Certain human-made pollutants (chlorofluorocarbons, or CFCs) react with stratospheric ozone, breaking it down into molecular oxygen, O 2

26 Ozone in the troposphere The layer of atmosphere closest to Earth s surface A human-made air pollutant Ground-level ozone does not replenish the ozone depleted in the stratosphere because ground-level ozone breaks down to form oxygen long before it drifts up to the stratosphere

27 Ozone in the troposphere A secondary air pollutant that forms when sunlight catalyzes reactions between NOx and volatile HC The most harmful component of photochemical smog Reduces air visibility & causes health problems Stresses plants & reduces their vigor A greenhouse gas global climate change

28 Grape leaf grown in clean air Damaged by ozone

29 Hazardous Air Pollutants (HAPs) HAPs are air pollutants that are potentially harmful & may pose long-term health risks to people who live & work around chemical factories, incinerators, or other facilities that produce or use them

30 Hazardous Air Pollutants (HAPs) or Air Toxics Chlorine Lead Hydrochloric acid Formaldehyde Radioactive substances Fluorides Present in low concentrations Also possible to have them at high concentrations locally

31 Sources of Outdoor Pollution 2 main human sources of primary air pollutants Transportation (mobile sources) Industries (stationary sources)

32 Mobile sources Automobiles & trucks Significant quantities of NOx, COx, PM, and HC as a result of combustion of gasoline

33 Stationary sources Electric power plants & other industrial facilities emit most of the particulate matter & SOx, NOx, HC, COx Combustion of fossil fuels, especially coal The top 3 industrial sources of toxic air pollutants Chemical industry Metals industry Paper industry

34 Urban Air Pollution Industrial smog Air pollution localized in urban areas is often called smog Industrial smog: principle pollutants are SOx & PM December 1952: 4000 Londoners died in the world s worst industrial smog incident An additional 8000 people died within the next 2 months Industrial smog is not a significant problem in HDCs today because of air quality laws & air-pollution-control devices

35 Urban Air Pollution Photochemical smog A brownish-orange haze formed by chemical reactions involving sunlight, NOx, HC First noted in Los Angeles in the 1940s Worst during the summer months

36 Several chemical reactions result in the complex mixture known as smog: ozone, peroxy acyl nitrates (PANs), nitric acid, and various organic compounds such as formaldehyde

37 Effects of Air Pollution Injures organisms Reduces visibility Attacks & corrodes materials such as metals, plastics, rubber, and fabrics Respiratory tracts of humans are particularly harmed by air pollutants Chronic lung disease, pneumonia, and cardiovascular problems

38 Effects of Air Pollution Reduce the overall productivity of crop plants Causes plants to decline & die when combined with other environmental stressors, such as extreme temperatures or prolonged droughts Air pollution is involved in Acid deposition Global climate changes Stratospheric ozone depletion

39 Controlling Air Pollutants Electrostatic Precipitator Electrode imparts a negative charge to particles in the dirty gas. Particles are attracted to the positively charged precipitator wall and then fall off into the collector

40 Controlling Air Pollutants Scrubber Mists of water droplets trap particulates in the dirty gas

41 Controlling Air Pollutants When emissions are not controlled With a scrubber system in place, most particulate matter is removed, leaving only steam

42 Ozone Depletion in the Stratosphere A form of oxygen that is a human-made pollutant in the troposphere but a naturally produced, essential component in the stratosphere

43 Ozone Depletion in the Stratosphere Ozone layer over Antarctica thins naturally for a few months each year. In 1985, however, stratospheric ozone thinning was first observed to be greater than could be explained by natural causes By 2000 it had reached the record size of 29.2 million km2

44 Ozone Depletion in the Stratosphere

45 Ozone Depletion in the Stratosphere A computer generated image of part of the Southern Hemisphere, taken on October 1, 2010, reveals the ozone thinning (bluish-purple area over Antarctica). The ozone-thin area is not stationary but moves about as a result of air currents Source: NASA

46 The Causes of Ozone Depletion Both chlorine- and bromine- containing substances catalyze ozone destruction Primary chemicals responsible for release of chlorine in the stratosphere: chlorofluorocarbons (CFCs) used as Propellants for aerosol cans Coolants in air conditioners and refrigerators Foam-blowing agents for insulation & packaging Solvents

47 Effects of Ozone Depletion Higher levels of UV radiation reach Earth s surface Several health problems in humans Cataracts Skin cancer Weakened immunity High levels of UV radiation may also damage crops & forests

48 Effects of Ozone Depletion These tumors of pigmented cells sometimes, but not always, arise from preexisting moles. Early diagnosis is important because this form of skin cancer spreads to other parts of the body and can be fatal.

49 Facilitating the Recovery of the Ozone Layer 1987 Montreal Protocol An agreement that originally stipulated a 50% reduction of CFC production by 1998

50 Acid Deposition Sulfur dioxide & nitric oxide emissions react with water vapor in the atmosphere to form acids that return to the surface as either dry or wet deposition

51 Acid Deposition Term acid rain in 1872 Robert Angus Smith, a British chemist, noticed that buildings in areas with heavy industrial activity were being worn away by rain

52 Effects of Acid Deposition

53 Air Pollution Around the World Smoke in Mexico City, Mexico Air pollution in Liaoning Province, China

54 Indoor Air Pollution The air in enclosed places such as automobiles, homes, schools, and offices may have significantly higher levels of air pollutants than the air outdoors The concentrations of certain indoor air pollutants may be 2 or 5 times greater- and sometimes >100 times- than outdoors. EPA considers indoor air pollution as one of the top 5 environmental health risks.

55 Sources of household air pollution