Chapter 18: Air Pollution

18.1 What Is the Nature of the Atmosphere?

The Atmosphere Consists of Several Layers

• Density varies→ Decreases with altitude
• Atmospheric pressure→ Decreases with altitude

Air Movements in the Troposphere Play a Key Role in Earth’s Weather and Climate

• Troposphere
  • 75–80% of the earth’s air mass
  • Closest to the earth's surface
  • Chemical composition of air
  • Rising and falling air currents
  • weather and climate
  • Involved in chemical cycling

The Stratosphere Is Our Global Sunscreen

• Stratosphere: Similar composition to the troposphere, with 2 exceptions
  • Much less water
  • O3, ozone layer
• Ozone layer: Filters 95% of harmful UV radiation and allows us and other life to exist on land

18.2 What Are the Major Outdoor Pollution Problems?

What is Air Pollution?

• Air pollution: Concentrations high enough to harm human health or alter the climate
• Natural sources
  • Dust blew by the wind
  • Pollutants from wildfires and volcanoes
  • Volatile organics released by plants
• Pollutants mix in the air to form industrial smog
  • Primarily as a result of burning coal and photochemical smog
  • Caused by emissions from motor vehicles, industrial facilities, and power plants

Air Pollution Comes from Natural and Human Sources

• Human sources: mostly in industrialized and/or urban areas
• Stationary sources: power plants and industrial facilities
• Mobile sources: motor vehicles

Some Pollutants in the Atmosphere Combine to Form Other Pollutants

• Primary pollutants: Emitted directly into the air
• Secondary pollutants: From reactions of primary pollutants
• Air quality improving in developed countries
• Less-developed countries face big problems
  • Indoor pollution: a big threat to the poor

Human Impact on the Atmosphere

• Burning Fossil Fuels
  • Adds CO2 and O3 to troposphere
  • Global Warming
  • Altering Climates
  • Produces Acid Rain
• Using Nitrogen fertilizers and burning fossil fuels
  • Releases NO, NO2, N2O, and NH3 into troposphere
  • Produces acid rain
• Refining petroleum and burning fossil fuels
  • Releases SO2 into troposphere
• Manufacturing
  • Releases toxic heavy metals (Pb, Cd, and As) into the troposphere

Criteria Air Pollutants

• EPA uses six "criteria pollutants" as indicators of air quality

1. Nitrogen Dioxide: NO2

2. Ozone: ground level O3

3. Carbon monoxide: CO

4. Lead: Pb

5. Particulate Matter: PM10 (PM 2.5)

6. Sulfur Dioxide: SO2

   1. Volatile Organic Compounds: (VOCs)

• EPA established for each concentration above which adverse effects on health may occur

Carbon Monoxide (CO)

• Properties of carbon monoxide: colorless, odorless, heavier than air, 0.0036% of the atmosphere
• Effects of carbon monoxide: binds tighter to Hb than O2, mental functions, and visual acuity, even at low levels
• Sources of carbon monoxide: incomplete combustion of fossil fuels 60 - 95% from auto exhaust
• Class of carbon monoxide: carbon oxides (CO2, CO)
• EPA Standard of carbon monoxide: 9 ppm
• 5.5 billion tons enter the atmosphere/per year

Nitrogen Dioxide (NO2)

• Properties of nitrogen dioxide: reddish brown gas, formed as fuel burnt in the car, potent oxidizing agent, include Nitric acid in the air
• Effects of nitrogen dioxide: acid rain, lung and heart problems, decreased visibility (yellow haze), suppresses plant growth
• Sources of nitrogen dioxide: fossil fuels combustion @ higher temperatures, power plants, forest fires, volcanoes, bacteria in soil
• Class of nitrogen dioxide: Nitrogen oxides (NOx)
• EPA Standard of nitrogen dioxide: 0.053 ppm

Sulfur Dioxide (SO2)

• Properties of sulfur dioxide: colorless gas with an irritating odor
• Effects of sulfur dioxide: produces acid rain (H2SO4), breathing difficulties, eutrophication due to sulfate formation, lichen and moss are indicators
• Sources of sulfur dioxide: burning high sulfur coal or oil, smelting or metals, paper manufacture
• Class of sulfur dioxide: sulfur oxides
• EPA Standard of sulfur dioxide: 0.3 ppm (annual mean)
• Combines with water and NH4 to increase soil fertility Suspend

Suspended Particulate Matter (PM10)

• Properties of particulate matter: particles suspended in air (<10 um)
• Effects of particulate matter: lung damage, mutagenic, carcinogenic, teratogenic
• Sources of particulate matter: burning coal or diesel, volcanoes, factories, unpaved roads, plowing, lint, pollen, spores, burning fields
• Class of particulate matter: dust, soot, asbestos, lead, PCBs, dioxins, pesticides
• EPA Standard of particulate matter: 50 ug/m3 (annual mean)

Ozone

• Properties of ozone: colorless, unpleasant odor, a major part of photochemical smog
• Effects of ozone: lung irritant, damages plants, rubber, fabric, and eyes, 0.1 ppm can lower PSN by 50%,
• Sources of ozone: Created by sunlight acting on NOx and VOC, photocopiers, cars, industry, gas vapors, chemical solvents, incomplete fuel combustion products
• Class of ozone: photochemical oxidants

Volatile Organic Compounds (VOC)

• Properties of VOCs: organic compounds (hydrocarbons) that evaporate easily, usually aromatic
• Effects of VOCs: eye and respiratory irritants; carcinogenic; liver, CNS, or kidney damage; damages plants; lowered visibility due to brown haze; global warming
• Sources of VOCs: vehicles (largest source), evaporation of solvents or fossil fuels, aerosols, paint thinners, dry cleaning
• Class of VOCs: HAPs (Hazardous Air Pollutants)
  • Methane
  • Benzene
  • Chlorofluorocarbons (CFCs), etc.
• Concentrations indoors up to 1000x outdoors
• 600 million tons of CFCs

Lead (Pb)

• Properties of lead: grayish metal
• Effects of lead: accumulates in tissue; affects kidneys, liver, and nervous system (children most susceptible); mental retardation; possible carcinogen; 20% of inner city kids have [high]
• Sources of lead: particulates, smelters, batteries
• Class of lead: toxic or heavy metals
• EPA Standard of lead: 1.5 ug/m3 • 2 million tons enter the atmosphere/per year

Chemical Reactions That Form Major Outdoor Air Pollutants

• Carbon monoxide: 2C + O2 → 2CO
• Carbon dioxide: C + O2 → CO2
• Nitric oxide: N2 + O2 → 2NO
• Nitrogen dioxide: 2NO + O2 → 2NO2
• Sulfur dioxide: S + O2 → SO2

Types of Smog

• Smog: A mixture between smoke and fog that produces unhealthy urban air
• Two Types
  • Sulfurous Smog / Industrial Smog / Fossil Fuels
  • Photochemical Smog / Sunlight & Pollutants

Sunlight Plus Cars Equal Photochemical Smog

• Photochemical Smog
  • Chemical composition
  • Sources
• VOCs + NOx + Heat + Sunlight yields
  • Ground-level O3 and other photochemical oxidants
  • Aldehydes
  • Other secondary pollutants

Several Factors Can Decrease or Increase Outdoor Air Pollution

• Outdoor air pollution may be decreased by

  1. Settling of particles due to gravity
  2. Rain and snow
  3. Salty sea spray from the ocean
  4. Winds
  5. Chemical reactions

• Outdoor air pollution may be increased by

  1. Urban buildings

  2. Hills and mountains

  3. High temperatures

  4. Emissions of VOCs from certain trees and plants

  5. Grasshopper effect

  6. Temperature inversions

     1. Warm air above cool air prevents mixing

18.3 What Is Acid Deposition and Why Is It a Problem?

Acid Disposition Is a Serious Regional Air Pollution Problem

• Acid deposition, acid rain
  • Chemical sources
  • Formation
  • Local versus regional problems
  • Effects of prevailing winds
  • Buffers

Effects of Acid Deposition

• Leaching of soil nutrients
• Lower crop yields
• Forest damage

18.4 What Are the Major Indoor Air Pollution Problems?

Indoor Air Pollution Developing Countries

• Developing countries: Indoor burning of wood, charcoal, dung, crop residues, coal
  • Poor suffer the greatest risk
• Who is at greatest risk from indoor air pollution?
  • Children under 5 and the elderly
  • Sick
  • Pregnant women
  • People with respiratory disorders or heart problems
  • Smokers
  • Factory workers
• Four most dangerous indoor air pollutants
  • Tobacco smoke
  • Formaldehyde
  • Radioactive radon-222 gas
  • Very small particles

Indoor Air Pollution Is a Serious Problem

• Other possible indoor air pollutants
  • Pesticide residue
  • Pb particles
  • Living organisms and their excrements
  • E.g., Dust mites and cockroach droppings
  • Airborne spores of molds and mildews

18.5 What Are the Health Effects of Air Pollution?

Your Body’s Natural Defenses against Air Pollution Can Be Overwhelmed

• Respiratory system protection from air pollutants
  • Role of cilia, mucus, sneezing, and coughing
• Effect of smoking and prolonged air pollution exposure
  • Chronic bronchitis
  • Emphysema

Air Pollution Is a Big Killer

• 2.4 million deaths per year world-wide
  • Mostly in Asia; 750,000 in China
  • 150,000 to 350,000 in the United States
  • Role of coal-burning power plants
• EPA: proposed stricter emission standards for diesel-powered vehicles
  • 125,000 die in the U.S. each year from diesel fumes
  • Emissions from one truck = 150 cars

18.6 How Should We Deal with Air Pollution?

Laws and Regulations Can Reduce Outdoor Air Pollution

• United States
  • Clean Air Acts: 1970, 1977, and 1990 created regulations enforced by states and cities
• EPA
  • National ambient air quality standards for 6 outdoor pollutants
  • NAPs: National emission standards for 188 hazardous air pollutants
  • TRI: Toxic Release Inventory

The Clean Air Act

• Congress found
  • Most people now live in urban areas
  • Growth results in air pollution
  • Air pollution endangers living things
• It decided
  • Prevention and control at the source were appropriate
  • Such efforts are the responsibility of states and local authorities
  • Federal funds and leadership are essential for the development of effective programs
• 1990 version
  • Acid rain, urban smog, toxic air pollutants, ozone depletion, marketing pollution rights, VOC’s
• 1997 version→ Reduced ambient ozone levels
  • Cost $15 billion/year -> save 15,000 lives
  • Reduce bronchitis cases by 60,000 per year
  • Reduce hospital respiratory admission 9000/year

Solutions for Stationary Source Air Pollution

• Prevention
  • Burn low sulfur coal or remove sulfur from coal
  • Convert coal to a liquid or gaseous fuel
  • Phase out coal use
• Reduction or disposal
  • Disperse emissions (which can increase downwind pollution)with smokestacks
  • Remove pollutants from smokestack gases
  • Tax each unit of pollution produced

Solutions for Motor Vehicle Air Pollution

• Prevention
  • Walk, bike, or use mass transit
  • Improve fuel efficiency
  • Get older, polluting cars off the road
• Cleanup
  • Require emission control devices
  • Inspect car exhaust systems twice a year
  • Set strict emission standards