1. Air Pollution and Stratospheric Ozone Depletion
Chapter 15
Air Pollution and Stratospheric Ozone Depletion

2. Air Pollution
Air pollution- the introduction of chemicals, particulate matter, or microorganisms into the atmosphere at concentrations high enough to harm plants, animals, and materials such as buildings, or to alter ecosystems.
Refers to pollution in the troposphere – first 16 km (10 miles) of atmosphere.

3. Major Air Pollutants
Sulfur Dioxide (SO2) – corrosive gas from combustion of coal and oil.
Respiratory irritant; adversely affects plant tissue
Also released in large quantities from volcanic eruptions
Nitrogen Oxides (Nox)
NO – colorless, odorless gas
NO2 – pungent, reddish-brown gas
Motor vehicles and stationary fossil fuel combustion
Natural sources – forest fires, lightening, microbial action in soil
Play a role in forming tropospheric ozone and smog
Carbon Oxides
Carbon monoxide (CO) – colorless, odorless gas that is formed during incomplete combustion – common emission in vehicle exhaust. In developing countries – poor ventilation when cooking with manure, charcoal, or kerosene.
Carbon dioxide (CO2) – colorless, odorless gas formed during complete combustion of fossil fuels and biomass.
Absorbed by plants during photosynthesis
Burning fossil fuels has contributed additional CO2 to atmosphere and is becoming a major pollutant.

4. Major Air Pollutants
Particulate Matter – solid or liquid particles suspended in air
Combustion of wood, animal manure biofuels, coal, oil, and gasoline
Diesel vehicles give off more in the form of black smoke
Also comes from road and rock-crushing operations
Volcanoes, forest fires, dust storms – natural sources
Size ranges from 0.01 micrometers to 100 micrometers
Human hair has a diameter = micrometers
PM10 – smaller than 10µm – concern to air pollution scientists because they are not filtered out by the nose and throat and can be deposited deep within the respiratory tract.
PM2.5 – greater health concern – deposited deep in respiratory tract and are composed of more toxic substances
Scatters and absorbs sunlight
Can cause reduces visibility known as haze – caused when particulate matter from air pollutions scatters light.

6. Major Air Pollutants
Photochemical Oxidants – formed as a result of sunlight acting on compounds such as nitrogen oxides and sulfur dioxide.
Harmful to plant tissue, human respiratory tissue, and construction materials
Smog – mixture of oxidants and particulate matter
Photochemical smog (Los Angeles-type smog, brown smog) – dominated by oxidants such as ozone
Sulfurous smog (London-type smog, gray smog) – dominated by sulfur dioxide and sulfate compounds.
Lead and Other Metals
Lead – trace metal occurs naturally in soils
Toxic to central nervous system (CNS)
Added to gas to improve vehicle performance – phased out between and 1996 – since then air concentration dropped considerably
Lead in paint in older buildings – chips off – can affect learning and intelligence especially in young children who may ingest due to sweet taste
Mercury – trace metal found in coal and oil – toxic to CNS
EPA regulates mercury through its hazardous air pollutants program – decreased air and water concentrations dramatically
Bioaccumulations – mercury concentrations in some fish have increased

7. Major Air Pollutants
Volatile Organic Compounds (VOCs) – organic compounds that become compounds at typical atmospheric temperatures
Many are hydrocarbons – compounds that contain carbon- hydrogen bonds, such as gas, lighter fluid, dry-cleaning fluid, oil-based paints, and perfumes
Compounds that give off a strong aroma – often VOCs – chemicals easily released into the air
Lead to formation of photochemical smog

9. Pollutants
Primary pollutants- polluting compounds that come directly out of the smoke-stack, exhaust pipe, or natural emission source.
Examples: CO, CO2, SO2, NOx, and most suspended particulate matter.
Secondary pollutants- pollutants that have undergone transformation in the presence of sunlight, water, oxygen, or other compounds.
Examples: ozone, sulfate and nitrate

10. Natural Sources of Air Pollution
Volcanoes
Lightning
Forest fires
Plants

11. Anthropogenic Sources of Air Pollution
On-road vehicles
Power plants
Industrial processes
Waste disposal
The Clean Air Act and its various amendments require that the EPA establish standards to control pollutants that are harmful to “human health and welfare.”
Through the National Ambient Air Quality Standards (NAAQS) the EPA periodically specifies concentration limits for each air pollutant.
For each pollutant the NAAQS note a concentration that should not be exceeded over a specified time period.
If a locality violates the air quality standard and does not make an attempt to make improvements, it is subject to penalties.

13. Trends in criteria air pollutants in the US have decreased between 1990 and 2008

14. The Chemistry of Smog Formation
During the day, in the presence of sunlight, if there is an abundance of nitrogen oxides in the atmosphere, but very few VOCs, ozone (O3) forms.
When sunlight decreases, nitrogen oxide is still present in the atmosphere and the ozone recombines with the NO and reforms into O2 + NO2.
When petrochemicals or VOCs are absent or limited, the cycle of ozone destruction and formation generally takes place with relatively small amounts of smog formation.
When VOCs are present, they combine with nitrogen oxide.
Nitrogen oxide is not available to break down ozone by recombining with it and a larger amount of ozone accumulates
Daytime accumulation of ozone in urban areas with an abundance of VOCs and Nox.
Trees and shrubs, and forest fires can contribute to photochemical smog in rural areas

16. Virtual sunlight: The LED screen shows the rising sun in Tiananmen Square which is shrouded with heavy smog on January 16, 2014 in Beijing, China.

17. Tourists in masks use mobile phone cameras to snap shots of themselves during a heavily polluted day on Tiananmen Square in Beijing, China

18. Thermal Inversions
Thermal Inversion- when a relatively warm layer of air at mid-altitude covers a layer of cold, dense air below.
The warm inversion layer traps emissions that then accumulate beneath it.

19. Acid Deposition
Acid deposition- occurs when nitrogen oxides and sulfur oxides are released into the atmosphere and combine with atmospheric oxygen and water. These form the secondary pollutants nitric acid and sulfuric acid.
These secondary pollutants further break down into nitrate and sulfate and hydrogen ions (H+) which cause the acidity in acid deposition.
Transformations occur over a number of days and pollutants may travels a thousand kilometers or more.
Acid deposition has been reduced in the US as a result of the Clean Air Act.

20. Acid Deposition

21. Effects of Acid Deposition
Lowering the pH of lake water
Decreased species diversity – a change pH change of 6.5 to 6.0 acidifies the lake and may cause developmental or reproductive problems in amphibians.
Below 5.0, most salamander species will die.
Mobilizing metals
Lower pH causes metals bound in organic or inorganic compounds in soils and sediments to be released into surface water.
Aluminum and mercury can impair physiological functioning of aquatic organisms – can lead to species loss.
Damaging statues, monuments, and buildings
When the hydrogen ions in acid deposition interacts with limestone or marble, the calcium carbonate reacts with H+ and give off Ca+.
More acidic the precipitation, the more H+ to interact with calcium carbonate.
Acropolis - Athens, Greece

22. Ways to Prevent Air Pollution
Removing sulfur dioxide from coal by fluidized bed combustion – granulated coal burned in close proximity to calcium carbonate – reduces sulfur dioxide emissions.
Heated calcium carbonate absorbs sulfur dioxide and produces calcium sulfate – used in production of gypsum wallboard (sheetrock), for houses.
Catalytic converters on cars – reduce nitrogen oxide and carbon monoxide emissions.
Scrubbers on smoke stacks – uses a combination of water and air that actually separates and removes particles. Particles removed in liquid or sludge form and clean gas exits.
Reduce emissions of SO2.
Baghouse filters – fabric filters that allow gases to pass through them but remove particulate matter.
Electrostatic precipitators – use an electrical charge o make particle coalesce so they could be removed.
Polluted air enters and the electrically charged particles within are attracted to negative or positive charges on the sides of the precipitator.

26. Innovative Pollution Control
Mexico City – permits cars to be driven every other day – license plates ending in odd numbers may be used one day with even-numbered on alternate days
China – during 2008 Beijing Olympics – government successfully expanded public transportation networks, imposed motor vehicle restrictions, and temporarily shut down a number of industries to reduce photochemical smog.
London – charging individual user fees to use roads at certain times of the day or within certain parts of the city.
Clean Air Act – buying and selling allowances that authorizes a power plant or industrial source to emit one ton of SO2 per year.
Facilities that emit above their allowances must pay a penalty
Sulfur allowances can be bought and sold on the open market
If emitters wanted to exceed their allowance they would need to purchase more allowances.
SO2 emissions in US has declined from 23.5 million metric tons in 1982 to 10.3 million metric tons in 2008

27. Stratospheric Ozone
The stratospheric ozone layer exists roughly kilometers above the Earth.
Ozone has the ability to absorb ultraviolet radiation and protect life on Earth.

28. Formation and Breakdown of Ozone
First, UV-C radiation breaks the bonds holding together the oxygen molecule O2, leaving two free oxygen atoms: O2 + UV-C -> O + O
Sometimes the free oxygen atoms result in ozone: O+ O2 -> O3
Ozone is broken down into O2 and free oxygen atoms when it absorbs both UV-C and UV-B ultraviolet light: O3 + UV-B or UV-C -> O2 + O

29. Anthropogenic Contributions to Ozone Destruction
Certain chemicals can break down ozone, particularly chlorine.
The major source of chlorine in the stratosphere is a compound known as chlorofluorocarbons (CFCs)
CFCs are used in refrigeration and air conditioning, as propellants in aerosol cans and as “blowing agents” to inject air into foam products like Styrofoam.

30. Anthropogenic Contributions to Ozone Destruction
When CFCs are released into the troposphere they make their way to the stratosphere.
The ultraviolet radiation present has enough energy to break the bond connecting chlorine to the CFC molecule, which can then break apart the ozone molecules.

31. Anthropogenic Contributions to Ozone Destruction
First, chlorine breaks ozone’s bonds and pulls off one atom of oxygen, forming a chlorine monoxide molecule and O2: O3 + Cl -> ClO + O2
Next, a free oxygen atoms pulls the oxygen atom from ClO, liberating the chlorine and creating one oxygen molecule: ClO + O -> Cl + O2
One chlorine atom can catalyze the breakdown of as many as 100,000 ozone molecules before it leaves the stratosphere.

32. Depletion of the Ozone Layer
Since the late 1970s, global ozone concentrations had decreased by more than 10%.
Depletion was greatest at the poles
Antarctic – ozone depletion was seasonal – occurring from August through November
Extremely cold weather conditions during the polar winter cause a buildup of ice crystals mixed with nitrogen oxide.
This provides a surface for the formation of the stable molecule Cl2, which accumulates as atmospheric chlorine interacts with ice crystals.
When sun reappears in spring, UV radiation breaks down this molecule into Cl again, which in turn catalyzes the destruction of ozone
Because almost no ozone had been formed in the dark polar winter, a large ozone “hole” occurs.
Decreased stratospheric ozone has increased the amount of UV-B radiation that reaches the surface of Earth.
UV-B – harmful to cells, reduces photosynthesis, increased skin cancer, cataracts
Significant increases in skin cancer have already been recorded, especially in countries near the ozone hole, such as Chile and Australia

33. Efforts to Reduce Ozone Depletion
Montreal Protocol on Substances that Deplete the Ozone Layer – signed in 1987 by 24 nations – committed to concrete steps toward a solution and resolving to reduce CFC production 50% by the year 2000.
A series of increasingly stringent amendments was eventually signed by more than 180 countries, requiring the elimination of CFC production and use in the developed world by 1996.
Because of these efforts, the chlorine concentration in the stratosphere has stabilized at about 5 ppb and should fall to 1 ppb by 2100.
– NASA research

34. Indoor Air Pollutants
Wood, animal manure or coal used for cooking and heating in developing countries.
Asbestos – long, thin, fibrous silicate mineral with insulating properties.
Was used as an insulator on steam and hot-water pipes and in shingles for building siding.
Greatest health risk – respiratory diseases such as asbestosis and lung cancer
When insulating materials become old or damaged fine fibers become airborne and can enter the respiratory tract.
Carbon Monoxide – result of malfunctioning exhaust systems – natural gas heaters
Colorless and odorless – occupants of house do not notice
CO binds with hemoglobin more efficiently than oxygen interfering with oxygen transport in the blood. Leads to oxygen deprivation and death.
Radon – Radon-222 – radioactive gas that occurs naturally from decay of uranium.
Seeps into a home through cracks in foundation or soil, or from drinking water from underlying rock, soil, or groundwater
Decays within 4 days to radioactive Polonium-210
Either can attach to dust in the air and then be inhaled.
EPA estimate 21,000 people die each year from radon-induced lung cancer
Radon detector, increase ventilation, seal cracks in basement
VOCs in home products – building materials, furniture, glues, paints
Formaldehyde – used to manufacture particle board and carpeting glue
Pungent smell from new carpeting
Found to cause cancer in lab rats and is a suspected human carcinogen

35. Sick Building Syndrome
Insulation and prevention of air leaks in order to reduce the amount of heating or cooling necessary for a comfortable existence
Reduces energy use – side effect of allowing buildup of toxic compounds and pollutants in an airtight space.
Causes Sick Building Syndrome
New buildings contain many products made with synthetic materials and glues that may not have fully dried out – outgassing occurs
Office buildings – large numbers of workers have headaches, nausea, throat or eye irritations, and fatigue
EPA identified 4 reasons:
Inadequate or faulty ventilation
Chemical contamination – glues, carpeting, furniture, cleaning agents, copy machines
Chemical contamination from outdoor sources – vehicle exhaust transferred in through air intakes
Biological contaminants – mold or pollen