1. Global Ozone Project Curriculum
Lesson 1:
Air Pollution Basics
Welcome to the GO3 Curriculum!  Here you will learn the fundamentals of air pollution with an emphasis on the highly important air pollutant: ozone.  Among other things, you will learn how ozone is formed in the atmosphere from other air pollutants, how its concentration is affected by meteorology (weather), and how it harms human health, crops and natural ecosystems such as forests.  You will learn about the "good" ozone in the stratosphere that protects us from harmful UV radiation from the sun and the "bad" ozone at ground level where we live and breathe.  Finally, we will discuss what can be done individually, nationally and internationally to reduce air pollution and its harmful effects throughout the world.
Rev 13

2. Learning Objectives
At the end of this lesson students will be able to:
Explain the role of the Clean Air Act and name the 6 major air pollutants regulated in the US.
Define the terms primary and secondary pollutants.
Identify that there are both Natural and Anthropogenic sources of air pollutants and name examples of each.
This first lesson introduces the basics of air pollution.  Here you will learn how air pollution caused large numbers of deaths in the 1950s, leading to enactment of the Clean Air Act in the U.S. and the formation of the Environmental Protection Agency to regulate air pollution.  We will survey the major air pollutants and learn how many of the chemical compounds we consider to be pollutants have natural sources as well.  We also will find how some air pollutants are not emitted to the atmosphere directly but formed in the atmosphere from chemical and photochemical reactions of other pollutants that are produced by human activities.
Lesson 1: Air Pollution Basics

3. What is Air Composed of?
Dry air is made up of approximately 78% nitrogen, 21% oxygen and 1% argon.  These are sometimes referred to as the "permanent gases".  The concentration of water vapor in the atmosphere is highly variable, depending on local weather conditions, and can be up to as much as 3% or more of the air molecules.  Carbon dioxide (CO2) makes up about 0.038% (or 380 parts-per-million) of the atmosphere.  Carbon dioxide is the most important anthropogenic greenhouse gas.  It's concentration is continually increasing due to fossil fuel burning and is already higher than the concentration shown on this slide.  The trace gases that make up air pollution are typically at the parts-per-billion level or about 1,000 to 10,000 times lower than carbon dioxide.  The "piece of the pie" shown as Trace Gases in this diagram is greatly exaggerated.  The correct size of the slice would be so small as to be invisible to the eye.  Even at very low concentrations, trace gases can be harmful to human health, crops and natural ecosystems.
Lesson 1: Air Pollution Basics

4. What is Air Pollution?
Air Pollutant: Any substance emitted to or produced in the atmosphere as a result of human activity in sufficient quantity to cause harm to plants, animals or materials.
Harm can be direct: human health effects, reduced crop yields, damage to rubber products such as tires, erosion of marble sculpture, etc.
Or indirect: e.g., climate change
Ozone is an example of an air pollutant that causes direct damage to human health, plants, and materials such as rubber, plastics and coatings.  Sulfur dioxide is another example of a pollutant that is harmful to human health and plants.  It reacts in the atmosphere to form sulfuric acid which damages marble sculptures.  We will discuss many other air pollutants that have direct effects.
Carbon dioxide is considered a pollutant even though it is not harmful to human health at the levels present in the atmosphere (we exhale ~5% CO2);  but CO2 is the major cause of global warming.  Another example of an indirect effect is damage to the ozone layer in the stratosphere.  As we will learn, chlorofluorocarbons, present at very low part-per-billion and levels, have caused depletion of the Earth's protective ozone shield, allowing additional harmful ultraviolet radiation to reach the Earth's surface.
Lesson 1: Air Pollution Basics

5. Air Pollution + Stagnant Weather Can Spell Disaster
1948 in Donora, PA
One of the worst air pollution episodes in the history of the U.S. occurred in Donora, Pennsylvania  beginning on October 27, 1948.  A strong temperature inversion developed with warm air at ground level trapped by a stable layer of cold air above.  This allowed the sulfur dioxide from U.S. Steel's Donora Zinc Works and its American Steel and Wire plant and other industrial pollutants such as nitrogen dioxide and fluorine to build up to toxic levels.  The  toxic gases mixed to form a yellowish acrid smog.  The smog continued until it began to rain four days later on October 31 (Halloween).  By that time 20 of the town's residents had died.  Wikipedia has a detailed description of this disaster at:
1948: Donora, PA at NOON
An air pollution episode killed 20 people, and half the town's 14,000 residents became ill due to emissions from industrial facilities and stagnant weather conditions.
Lesson 1: Air Pollution Basics

6. Air Pollution + Stagnant Weather Can Spell Disaster
1952 in London, England
Nelson’s Column in the 1958 smog
Nelson’s Column today
Perhaps the worst air pollution event of all time, and certainly the worst air pollution for the U.K., occurred in London in  December 1952.  Like the air pollution disaster of Donora, Pennsylvania discussed in the previous slide, lethal levels of pollutants built up because of a temperature inversion.  We will discuss the role of meteorology and temperature inversions later in this course.  The "Great Smog of '52" or "Big Smoke" caused the death of between 4,000 and 12,000 people, with about 100,000 people being made ill.  The smog was not caused by a particular industry but by the burning of sulfur-rich coal in homes for heating.  This disaster finally raised awareness of the seriousness of air pollution, leading to the U.K.'s Clean Air Act of 1956.  More details can be found on Wikipedia:
An air pollution episode killed between 4,000 and 12,000 people. 100,000 residents became ill due to emissions from industrial facilities and coal burning during stagnant weather conditions.
Lesson 1: Air Pollution Basics

7. Clean Air Act
After the deadly US air pollution event of 1948, it was clear that air quality needed to be regulated to ensure that such severe pollution events didn’t happen again.
The US passed the first Clean Air Act in 1963.
The Clean Air Act of 1970 gave the US Environmental Protection Agency (EPA) the authority to regulate air pollution and identified six Criteria Pollutants to monitor.
The first air pollution legislation in the U.S. was the Air Pollution Control Act of 1955.  This act formally recognized the problem of air pollution but relegated all authority over matters of air pollution to the states.  The role of the federal government was strictly advisory.  Finally, in 1963 the U.S. Congress passed the first Clean Air Act, which provided the federal government with authority to regulate air pollutants, and the 1970 Clean Air Act Extension established  the Environmental Protection Agency to enforce the act.  Important amendments to the Clean Air Act occurred in 1977 and 1990.  Various states have enacted their own clean air legislation over the years.  Especially notable is California, which often leads the federal government in establishing more restrictive regulations of air pollutants. 
Lesson 1: Air Pollution Basics

8. Clean Air Act Six Criteria Air Pollutants to monitor:
Carbon Monoxide (CO)
Lead (Pb)
Nitrogen Dioxide (NO2)
Particulate Matter (PM2.5 and PM10)
Ozone (O3)
Sulfur Dioxide (SO2)
The Clean Air Act requires the EPA to establish National Ambient Air Quality Standards for "criteria" (or "priority") pollutants.  This slide lists the first six criteria pollutants to be regulated.  These six pollutants are still widely monitored and regulated and provide a benchmark for air quality.  Over the years, many more significant air pollutants have been identified.  Under the 1990 Clean Air Act, another 187 "Hazardous Air Pollutants (HAPs)" or "Air Toxics" became regulated as well.  Examples include benzene, which is found in gasoline; perchloroethylene which is emitted from some dry cleaning facilities; and methylene chloride, which is used as a solvent and paint thinner in many industries.  Also included are dioxin, asbestos, toluene and certain metals such as cadmium, mercury, chromium and lead compounds.  Many of the Air Toxics are carcinogens (cancer causing).
Lesson 1: Air Pollution Basics

9. Examples of Sources for the Six Criteria Pollutants
O3 – Ozone
Ozone: Formed by the interaction of sunlight with other other pollutants: NO, CO, and Volatile Organic Compounds (VOCs)
NO2 – Nitrogen Dioxide
Car exhaust and Electricity Generation produce NO during combustion, which gets converted into NO2 in the atmosphere
CO – Carbon Monoxide
All combustion processes such as car exhaust and Electricity Generation 1 2 3
The common sources of three of the priority pollutants are listed here.  There are no significant human emissions of ozone; as we will learn in more detail, ozone (O3) is formed in the reaction of sunlight with a carbon source and oxides of nitrogen.  All three ingredients are necessary to make ozone at ground level.
Similarly, there are no large anthropogenic sources of nitrogen dioxide (NO2).  All combustion sources (burning of fuels such as gasoline, coal and natural gas) produce nitric oxide (NO), which reacts in the atmosphere with ozone and other oxidants (peroxy free radicals, RO2, ultimately derived from ozone) to form NO2.  Nitrogen dioxide is the crieria pollutant that is regulated, rather than NO, because it as orders of magnitude more toxic than NO.  In fact, NO is used in inhalation therapy to treat premature babies, and in that application there is a huge concern for removing any NO2 impurity from the source gas.
Carbon monoxide (CO) is a toxic gas because it competes with oxygen for binding to hemoglobin in red blood cells.  It is an odorless gas (unlike ozone) and can reach dangerous concentrations without being noticed.  For this reason, people are urged to have CO detectors in their homes if the home is heated by a natural gas or heating oil furnace.  Carbon dioxide can be a serious problem in tunnels where auto exhaust accumulates and cause accidents by making the driver sleepy.  Carbon monoxide is produced when fuels are not burned efficiently so that not all of the carbon is oxidized all the way to CO2.  For example, if automobile engines are adjusted to be "fuel rich", they will produce larger amounts of CO, and the car will have poor fuel efficiency since not all of the energy can be derived from the fuel combustion is released.  Because of the economic incentive to be as efficient as possible, CO emissions from electrical power plants, which burn either coal or natural gas, kept very low.  
O3, NO2, and CO will be discussed further in Lesson 2
Lesson 1: Air Pollution Basics

10. Examples of Sources for the Six Criteria Pollutants
PM2.5,10 – Particulate Matter
Car Exhaust, Electricity Generation, Fires, and Road dust
Pb – Lead
Iron smelters and other industrial processes.
Before it was banned, leaded gasoline was a major contributor to lead in the atmosphere.
SO2 – Sulfur Dioxide
Electricity Generation from burning of coal. 4 5 6
The principal sources of the remaining three criteria pollutants are given here.  Particulate matter (PM) is measured as PM2.5 and PM10.  The subscripted numbers refer to the sizes of the particles.  Originally, only PM10, which refers to the mass of particles in a cubic meter of air having sizes less than 10 micrometers (µm) in diameter, was measured and regulated.  (By comparison, a red blood cell has a diameter of ~5 µm.)  However, the health effects of particulate matter depend on the particles being inhaled into the lungs.  The nose and throat remove nearly all particles larger than 10 µm ("course particles") and a large fraction of the particle larger than 2.5 µm.  The fine particles smaller than 2.5 µm are correlated with the adverse health effects associated with pulmonary diseases such as asthma and COPD (Chronic Obstructive Pulmonary Disease).  Particulate matter also is responsible for reduced visibility and the "brown cloud" that often hangs over cities.  Short wavelengths of light (e.g., blue light) are more strongly scattered by small particles than are long wavelengths (e.g., red light), causing the pollution layer to appear brown in color.
Lead (Pb) is a highly toxic element that affects the heart, bones, intestines, kidneys, reproductive organs and nervous system.  Lead poisoning has been a problem for thousands of years; the Romans sweetened their wine with lead salts, for example, and it is thought that this led to insanity of some of the Roman emperors.  Lead is of particular concern for children because it interferes with the development of the brain, causing permanent learning and behavioral disorders -- and even death.  Lead levels in blood have been correlated with reduced IQ and an increase in violent criminal behavior.  Lead poisoning of children, especially in poor neighborhoods, was at one time a very serious problem due to ingestion (pica) of paint flakes from houses painted prior to World War II when leaded paint widely used.  Lead smelters, which release lead in aerosol form, have been a large source of dangerous air pollution throughout the world.  The use of tetraethyl lead as an anti-knock agent in gasoline was developed in the 1920s and became widely used throughout the world.  It was discovered in the 1960s that burning leaded gasoline was poisoning our population, and leaded gasoline was finally banned for automobiles in the U.S. in the 1970s, although it is still used in light aircraft.  Also, many countries throughout the world still use leaded gasoline.
The main source of sulfur dioxide (SO2) to the atmosphere is burning of sulfur-containing coal.  Sulfur dioxide is a toxic gas like ozone and NO2, but it also reacts in the atmosphere to form sulfuric acid.  "Acid rain" contains both sulfuric acid and nitric acid formed from oxides of nitrogen.  Unlike lakes with limestone floors which can neutralize acid rain, the pH is lowered by acid rain for lakes with granite floors -- and in those lakes fish cannot live and reproduce.  The effects of acid rain on lakes, forests and other natural ecosystems led the EPA to regulate emissions of power plants through a "cap and trade" program beginning in the 1990s.  This led to installation of scrubbers on the smokestacks of coal-fired power plants and has greatly reduced the atmospheric levels of sulfur dioxide in the U.S. over the past two decades.  However, sulfur dioxide remains a serious air pollutant throughout much of the word, especially in rapidly developing countries. 
O3, NO2, and CO will be discussed further in Lesson 2
Lesson 1: Air Pollution Basics

11. Primary and Secondary Pollutants
Primary Pollutants are emitted directly from various sources and cause harm in their emitted state.
Examples of Primary Pollutants: NO, SO2, CO, CO2
Secondary Pollutants result from chemical transformations in the atmosphere.
Examples of Secondary Pollutants: O3, H2O2, HNO3, H2SO4, Nitrate and Sulfate Particles
Some of the principal pollutants emitted directly to the atmosphere include NO, CO, CO2 SO2, volatile organic compounds (VOCs) and some particulate matter such as soot.  The pollutants are sometimes referred to as "primary pollutants".
Ground level ozone, the pollutant of greatest interest to this course, is a "secondary pollutant" because there are no significant anthropogenic sources of ozone to the atmosphere.  Some other examples of secondary pollutants are hydrogen peroxide (H2O2), nitric acid (HNO3), sulfuric acid (H2SO4) and nitrate and sulfate particles formed from these acids.  Nitrogen dioxide is mostly a secondary pollutant, since combustion sources emit almost entirely NO as the only oxide of nitrogen.  Many oxidized products of hydrocarbons are secondary pollutants as well; for example, formaldehyde, acetaldehyde, formic acid, acetic acid, and many, many others.
Lesson 1: Air Pollution Basics

12. Natural and Anthropogenic Sources
There can be two sources of these compounds in the air:
Natural
Certain atmospheric gases are created by natural sources like trees, swamps, and oceans.
Anthropogenic
These gases are formed from human activity like cars and power plants.
In addition to the anthropogenic emissions we have discussed, there are large emissions to the atmosphere by nature itself.  Trees emit volatile organic compounds (VOCs) such as isoprene and various terpenes that are highly reactive in the atmosphere.  The Smoky Mountains get their name, for example, from a haze that develops because of reactions of terpenes in the atmosphere to form particles that scatter light.  President Ronald Reagan once famously said, "Trees cause more pollution than automobiles do."  His point was that we don't need to regulate automobile emissions because natural sources of compounds to the atmosphere are much larger.  As we shall see, things are not that simple.  Natural sources tend to be spread over large areas and are not concentrated in one small area such as an urban center.  And, anthropogenic pollutants such as the oxides of nitrogen react with natural emissions to form even more toxic compounds such as ozone that are not emitted by either nature or humans. Without the automobile emissions, the VOCs from trees would be benign, but with them, dangerously high levels of air pollutants are formed.  So, we do need to worry about anthropogenic emissions.
There are many important natural emissions to the atmosphere.  Some examples include:
CO2 from bacterial respiration (balanced out the uptake of CO2 by photosynthesis prior to human civilization)
CO, NO and N2O from bacteria in soils and oceans; the N2O from bacteria actually depletes the natural ozone layer by about 50%
NO and O3 from lightning
Ammonia (NH3) from bacterial decomposition of plant and animal matter
CH4, H2 and H2S from anaerobic bacteria in swamps where oxygen levels are low
Dimethyl sulfide from phytoplankton in the oceans (react in the atmosphere to form cloud condensation nuclei and alter the local climate)
SO2 and other gases from volcanoes
CO2, CO, VOCs, NO, NO2 and many other compounds from wildfires
These natural emissions can themselves be toxic; for example, the people of Pompey died from exposure to volcanic gases such as sulfur dioxide. As we shall see, natural emissions must be considered when evaluating the effects of anthropogenic emissions.
Lesson 1: Air Pollution Basics

13. Examples of Natural Sources
Termites
Believe it or not, termites’ digestive systems emit a significant amount of Methane
Lightning
Lightning creates Nitrogen Oxides (NOx)
Trees
Trees emit Volatile Organic Compounds (VOCs)
Three examples of natural emissions are highlighted here.  Lightning and trees were discussed in the previous slide.  Interestingly, the biomass of termites (~250 trillion) in the world is much, much greater than that of humans.  Termites, which digest cellulose, emit ~20 million tons of methane to the atmosphere each year, corresponding to about 4% of the total source of methane to the atmosphere.  The methane is actually produced by symbiotic bacteria that reside in the guts of the termites.  Methane also is produced by enteric fermentation in the guts of domesticated cattle, buffalo, sheep and goats and currently amounts to ~140 million tons/year.
Lesson 1: Air Pollution Basics

14. Examples of Anthropogenic Sources
Point very concentrated sources of pollution
Power Plants
Gas Pipelines
Area more diffuse sources of pollution
Cows
Paints, Architect-ural Coatings
On-Road
Cars
Trucks
Off-Road
Airplanes
Construction Equipment
Lawn Mowers
Separated into four Categories:
Another categorization of air pollutants relates to where and how they are released to the atmosphere.  This slide shows examples of Point, Area, On-Road and Off-Road emissions.
Lesson 1: Air Pollution Basics

15. Air Quality Index
A daily measure of the quality of the air generally published along with weather reports based on the amount of the six criteria pollutants in the air.
The Air Quality Index or AQI was developed as a way to easily convey the severity of air pollution to the public.  The AQI is published every day to allow people to make decisions about how much time to spend outdoors, whether or not to exercise (exercise can exacerbate health effects of air pollution), how much medication to take if you suffer from a pulmonary disease such as asthma, etc.
Lesson 1: Air Pollution Basics

16. Air Quality Index Levels of Health Concern Meaning 0-50
Numerical Value
Meaning
0-50
Good – Air Quality is considered satisfactory, and air pollution poses little or no risk.
51-100
Moderate – Air Quality is acceptable; however, for some pollutants there may be a moderate health concern for a very small number of people who are unusually sensitive to air pollution.
Unhealthy for Sensitive Groups – Members of sensitive groups may experience health effects. The general public is not likely to be affected.
151 – 200
Unhealthy – Everyone may begin to experience health effects; members of sensitive groups may experience more serious health effects.
Very Unhealthy – Health alert: everyone may experience more serious health effects.
> 300
Hazardous – Health warnings of emergency conditions. The entire population is more likely to be affected.
The Air Quality Index is color coded from green (good) through orange (unhealthy for sensitive groups), red (unhealthy for everyone) and purple (hazardous), as seen in this chart.  The AQI is based on the single priority pollutant that is the most unhealthy on that day and does not take into account any synergistic effects of high concentrations of multiple pollutants.  In the U.S., AQI typically is based on PM2.5 during the winter or either PM2.5 or ozone during the summer.  The other four criteria pollutants (CO, Pb, NO2, SO2) seldom contribute to the calculated API.
The current value of the AQI is provided by the EPA's AIRNow website and provided by many weather sources as well.
A daily measure of the quality of the air generally published along with weather reports based on the amount of the six criteria pollutants in the air.
Lesson 1: Air Pollution Basics