THEDUALNATUREOFOZONE
StratosphericandTroposphericOzone
by: Daniel Cohan Ph.D. and Remelia Arpino June, 2012 INTRODUCTION This lesson packet contains two lessons on ozone: Stratospheric Ozone and Tropospheric Ozone. This is the high school version of the Rice Air Curriculum, originally developed by Dr. Daniel Cohan and Kavita Venkateswar in 2009. Its primary objectives are to provide high school teachers of Environmental Systems or similar courses with curricular materials for engaging students in interactive and inquiry‐
based learning about ozone in both the stratosphere and troposphere. Each lesson is divided into two sections. The first section is the teaching guide that utilizes the 5E lesson plan format and the second section is the reproducible student materials. The suggested activities include collaboration among students, use of technologies like computers for research, use of apparatuses to measure weather conditions and ozone on school campuses, and a chance to develop and apply their critical thinking skills in designing their own experiment in the second lesson. Since the Houston region has long struggled to meet the federal air quality standards for ground‐level tropospheric ozone, it is hoped that at the end of the lessons, students will actively participate in considering how they can reduce emissions that cause the formation of tropospheric ozone. Teaching TheDualNatureofOzone:
Guide STRATOSPHERICOZONE
Adapted by Remelia Arpino from the Rice Air
Curriculum by Daniel Cohan and Kavita Venkateswar
OBJECTIVE This lesson focuses on stratospheric (high‐level) ozone, which protects us from the harmful radiation of the sun. The lesson explains how ozone naturally forms from oxygen and sunlight in the stratosphere, and distinguishes between the protective stratospheric ozone layer and the tropospheric ozone pollution that forms near the ground (covered in more detail in the Tropospheric Ozone Lesson). Students will look at how certain chemicals can damage stratospheric ozone and how the Montreal Protocol and the efforts of some companies and agencies are helping to protect the ozone layer. Students will be active participants throughout the whole lesson and it is hoped that at the end of the lesson, they will gain a deeper understanding of the stratospheric ozone. In preparation for the subsequent lesson about tropospheric ozone, students in the Explore activity will begin to measure ground‐level ozone and meteorological factors that are related to tropospheric ozone formation. Their skills in this investigation will be used in the next lesson for the inquiry lab. Figure 1. Stratospheric ozone forms naturally and protects us from ultraviolet radiation. Tropospheric ozone forms from air pollutant emissions and harms human health. Credit: US Nuclear Regulatory Commission: Ozone: Good Up High, Bad Nearby. BACKGROUND INFORMATION Most of the oxygen in the atmosphere, and the type that we need to sustain life, has two atoms per molecule (O2). Ozone, by contrast, has three oxygen atoms (O3). Ozone forms naturally in the stratosphere when intense ultraviolet radiation (UV‐C) from the Sun splits an oxygen molecule (O2) into two O atoms. Each O can then combine with another O2 to form O3. About 90 percent of the ozone in the Earth’s atmosphere is found in what is known as the ozone layer in the stratosphere (about 10‐30 miles above Earth’s surface). The ozone layer absorbs most of the Sun’s ultraviolet radiation to shield us from these damaging rays. Ultraviolet rays can cause a range of negative effects: they can cause cancer, burn skin, damage eyes, weaken the human immune system, and harm both plants and animals. In fact, estimates show that a one percent reduction in the ozone layer results in a two to five percent increase in the number of cases of cancer! Certain air pollutants can damage the ozone layer. The most dramatic depletion of the ozone layer is the Antarctic ozone hole. In the early 1980s, scientists discovered major thinning of the ozone layer above Antarctica during springtime1. In fact, they observed nearly 70% less ozone than had been found there previously! Scientists realized that the depletion of the ozone layer is caused by the release of certain chemicals such as chlorofluorocarbons (CFCs) into the atmosphere. Just a few decades ago, CFCs were used in air conditioners, aerosol sprays, and cleaning products. When CFCs reach the stratosphere, they react with the sunlight to release chlorine atoms, which can destroy ozone molecules. In 1989, an international agreement known as the Montreal Protocol was signed to ban the most destructive ozone‐depleting gases and preserve the ozone layer. If the agreement is adhered to, it is hoped that the ozone layer will completely recover by 2050. As we have seen, the ozone layer in the stratosphere is a vital layer of protection for the Earth. This layer that contains most of the atmosphere’s ozone is far above the air that we breathe every day, and even above the altitude where most airplanes fly. However, when ozone forms near the surface in the troposphere, where humans breathe, it is an air pollutant that can harm our lungs and the natural environment. This tropospheric ozone is the same molecule as in the stratosphere. However, in the troposphere, ozone forms in very different ways than in the stratosphere. We’ll learn more about tropospheric ozone in a separate lesson. 1
The dramatic thinning of ozone over the South Pole does not last for the entire year. Instead, it usually occurs in September or October (Antarctic springtime) and “fills in” or disappears by December. Special conditions in the Antarctic winter make its stratospheric ozone especially sensitive to depletion by chlorine when the sun returns in the early spring. Outside of Antarctica, slight reductions in stratospheric ozone have also been observed over most of the planet. TEXASSTANDARDS
TEXASESSENTIALKNOWLEDGEANDSKILLS(TEKS)
Environmental Systems TEKS 9: The student knows the impact of human activities on the environment. The student is expected to: A. Identify causes of air, soil, and water pollution, including point and nonpoint sources; B. Investigate the types of air, soil, and water pollution such as chlorofluorocarbons, carbon dioxide, pH, pesticide runoff, thermal variations, metallic ions, heavy metals, and nuclear waste; C. Examine the concentrations of air, soil, and water pollutants using appropriate units; D. Describe the effect of pollution on global warming, glacial and ice cap melting, greenhouse effect, ozone layer, and aquatic viability; E. Analyze past and present international treaties and protocols such as the environmental Antarctic Treaty System, Montreal Protocol, and Kyoto Protocol. TEXASCOLLEGEANDCAREERREADINESSPROGRAM(CCRS)
SCIENCESTANDARDSWITHPERFORMANCEINDICATORS
I.
Nature of Science A.
Cognitive skills in science 1. Use creativity and insight to recognize and describe patterns in natural phenomena. 2. Rely on reproducible observations of empirical evidence when constructing, analyzing, and evaluating explanations of natural events and processes. B.
Collaborative and Safe working practices 1. Collaborate on joint projects. 2. Demonstrate skill in the safe use of a wide variety of apparatuses, equipment, techniques, and procedures. C.
Current scientific technology 1. Use computer models, applications, and simulations D.
Effective communication of scientific information 1. Use several modes of expression to describe or characterize natural patterns and phenomena. These modes of expression include narrative, numerical, graphical, pictorial, symbolic and kinesthetic. II.
Foundation Skills: Scientific Applications of Mathematics A.
Understand the real number system and its properties 1. Calculate the sums, differences, products and quotients of real numbers. III.
Foundation Skills: Scientific Applications of Communication A.
Scientific Reading 1. Set up apparatuses, carry out procedures, and collect specified data from a given set of appropriate instructions. B.
Presentation of scientific /technical information in appropriate formats for various audiences 1. Prepare and present scientific/technical information in appropriate formats for various audiences. C.
Research skills/information literacy 1. Use search engines, databases, and other digital electronic tools effectively to locate information IV.
Cross‐Disciplinary Themes A.
Change over time/equilibrium 1. Recognize patterns of change V.
Environmental Science A.
Earth systems 1. Know the major features of the atmosphere B.
Human practices and their impacts 1. Understand how human practices affect air, water and soil quality. ENGAGE
Option 1: Brainpop Video ‐ Ozone Layer (Use this option if you have access to Brainpop.com otherwise, use option 2.) Materials: (for Option 1 and 2) For each group: Labels and diagram of the three layers namely: troposphere, ozone layer and stratosphere (SM‐1) Procedure: 1. Before showing the video, have students identify the three layers namely; troposphere, ozone layer and stratosphere by placing the correct labels in the diagram. Use SM‐1 material for this preliminary activity. 2. Have students watch the short video on ozone layer. 3. At the end of the video, ask students the following questions: a. How many oxygen atoms are there in an ozone molecule? b. What is the role of the ozone layer? c. What chemicals damage the ozone in the stratosphere? d. What government agency oversees programs designed to help the ozone layer? Option 2: You Tube Video: NASA: Exploring Ozone Procedure: 1. Before showing the video, have students identify the three layers namely; troposphere, ozone layer and stratosphere by placing the correct labels in the diagram. Use SM‐1 material for this preliminary activity. 2. Go to http://www.youtube.com/watch?v=qUfVMogIdr8 and have students watch the short video from NASA. 3. At the end of the video, ask students the following questions: Facilitation Questions: 1. How does stratospheric ozone protect life on earth? 2. What chemicals do you know that could damage the stratospheric ozone? 3. In addition to those chemicals, what are the other ingredients or factors known to deplete the ozone? EXPLOREPARTI
Teacher notes: The first explore activity will introduce students to the equipment that is used to monitor ground‐level ozone. It is important that they will develop the skills of using all the equipment listed below since they will be doing an inquiry lab in the next lesson. Do not forget to emphasize in this activity that they are measuring ground‐level (tropospheric) ozone, not stratospheric ozone. Teacher Preparation: Print the SM‐2 (Rice Air Curriculum: Ozone and Meteorology Data Sheet) and SM‐3 (Cloud Guide) for each group of students. Materials (one for each group):  Rice Air Curriculum: Ozone and Meteorology Data Sheet (SM‐2)  Cloud Guide (SM‐3)  Ozone strips  Ozone scanner 
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Hygro‐thermometer Infrared Thermometer Wind vane Thermal glove Procedure: 1. Take your students outside the classroom and have them measure the different parameters listed in the Ozone and Meteorology Data Sheet. Note: Be sure to review the GLOBE Protocol for Ozone. It is important that the ozone strip must be exposed for at least an hour. Make the necessary adjustments according to your class time. 2. Ask your students to record the beginning of class data in their data sheet. 3. Repeat the procedure after an hour and have your students record the end of class data in their data sheet. Facilitation Questions: 1. What is the difference between the beginning and end of class data? 2. How do you account for the difference of the data? EXPLOREPARTII
Teacher Preparation: Make copies of the Introduction to Ozone Cards for your student groups. Procedure: 1. Divide the class into seven (7) groups. 2. Assign one ozone card (SM‐4) to each group of students. 3. Instruct the students to read, brainstorm and discuss the information in the card for 15 minutes. 4. Remind them that after the activity, they are going to present it to the class for discussion. Give them an additional 10 minutes to prepare visual materials that would help them in the delivery of the information. EXPLAIN
Teacher Preparation: Make copies of SM‐5 (Note‐taking worksheet) for individual student. This will keep each student focused during the presentation. Vocabulary 
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Ozone Oxygen molecule Oxygen atoms Ozone layer 
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Stratospheric ozone Ultraviolet rays Electromagnetic spectrum Chlorofluorocarbon  Montreal Protocol  Antarctic ozone hole Procedure 1. Give students 5 minutes to prepare for their presentation. 2. Distribute SM‐5 to individual student for note‐taking during presentation. 3. Each group of students will explain the information in the card to the class. Note: Be sure to clarify things before proceeding to the next group. Facilitate the discussion by asking questions. ELABORATE
Teacher Notes: The elaborate or extension activity is an online research activity. Students are going to read the ‘Achievements in Stratospheric Ozone Protection Progress Report’ by the US Environmental Protection Agency. The information that they will gather from this report will enhance their understanding on the cause of stratospheric ozone depletion as well as the efforts of companies and agencies back then and now to save the ozone layer. This task can be given as a homework or in‐
class assignment. Teacher Preparation: If your access to computers is through the computer lab, be sure to reserve it in advance for this lesson. Make copies of SM‐6 for individual student. Materials:  Computers  Achievements in Stratospheric Ozone Protection Worksheet (SM‐6)  Pens/pencils
Procedure: 1. Distribute the SM‐6 to individual student. 2. Ask them to type ‘http://www.epa.gov/ozone/downloads/spd‐annual‐report_final.pdf’ into their internet browser. The first page of the document should be: ‘Stratospheric Ozone Protection Progress Report.’ 3. Instruct the class that they are going to read the whole document and answer the questions in the worksheet. EVALUATE
Teacher Preparation: Print copies of the Summative Assessment (SM‐7). Procedure: 1. Distribute the SM‐7 to each student. 2. Assess the students by giving the 5‐question summative assessment. Answer Key 1. D 2. D 3. A 4. B 5. C Student TheDualNatureofOzone:
Materials TROPOSPHERICOZONE SM‐1 SAVE SMOG CITY 2 FROM OZONE WORKSHEET Worksheet Courtesy of the U.S. Environmental Protection Agency and Sacramento
Air Quality Management District http://www.smogcity2.org/smogcity.cfm?preset=ozone Direction: Follow the instructions listed below. Be sure to answer the questions associated to some instructions in the activity. 1. Access the Smog City 2 web site at www.smogcity2.org. 2. Select “Save Smog City 2 from Ozone.” 3. Once Smog City 2 loads to your computer, take note of the areas of Smog City 2, including Weather Conditions, Emissions Levels and Population. All areas have “clickable” choices. Mouse‐over or click on the choices. • NOTE: in the information box at the bottom of the screen, there is information about each choice. 4. Notice how each of the choices are pre‐set to a certain level. These are called the default settings. You can use the reset button at any time to return to the default settings. In the chart below, circle or highlight the default setting for each choice. The first setting, Sunlight, has already been completed for you. A. Weather Conditions Weather Conditions Choices Included in the Area Sunlight Inversion Layer Wind Speed Maximum Daily Temperature Clear Partly Cloudy Cloudy No inversion Low inversion High Inversion Calm Light Breeze Breezy Windy 30ºF 40ºF 50ºF 80ºF 90ºF 100ºF 110ºF B. Emission Emission Energy Sources Cars and Trucks Off Road Vehicles Consumer Products Industry Choices Included in the Area Some energy sources produce more smog‐producing emissions than others.(level 1 is cleaner sources like a wind or solar technology, level 3 produces more smog like a coal‐fired power plant) Levels: 1 2 3 This includes Passenger vehicles (all sizes), large and medium trucks, motorcycles Levels: 1 2 3 4 5 This includes airplanes, trains, power boats, earth movers, tractors, harvesters, forklifts, bulldozers, backhoes Levels: 1 2 3 4 5 This includes paint thinner, charcoal lighter fluid, glue or other adhesives, gasoline Levels: 1 2 3 4 5 This includes manufacturing facilities, power plants, oil refineries/storage/distribution centers, food and agricultural processing Levels: 1 2 3 4 5 C. Population Population Choices Included in the Area In Smog City 2, you can increase the Population in Smog City 2 affects air quality. Changing population, as shown by the “total emissions” population from near‐zero to about two chart and the emission sources in the cityscape, affects million people. VOCs, NOx and SO2. The compounds react to form Levels: 1 2 3 4 5 ground‐level ozone and particle pollution. When temperatures are cool, changing population also changes the usage of wood‐burning stoves, which emit particle pollution. 5. Observe the AQI (Air Quality Index) box in the lower right corner. The default settings, which are circled above, result in a “red”, or “Unhealthy” AQI for ground level ozone. The health message is: “Active children and adults, and people with respiratory disease, such as asthma, should avoid prolonged outdoor exertion; everyone else, especially children, should limit prolonged outdoor exertion.” Scenario 1: Emission Sources
1. Minimize the “Save Smog City 2 from Ozone!” instructions at the top of the screen. 2. Turn only Cars and Trucks control to 1. Leave all other choices at the default settings. Record what happens on the Student Worksheet in the table below. Use the reset button to return the Cars and Trucks control to 4, so all controls are in default position. 3. Turn only Off Road down to 1. Leave all other settings alone. Record what happens on the Student Worksheet. Use the reset button to return the Off Road control to the middle setting, so all controls are in default position. 4. Adjust each of the remaining controls noted in red and record the result in Data Table 1. Data Table 1 Energy Cars & Off Consumer Industry Air Quality Index (AQI) Sources Trucks Road Products Color | message | value default 2 4 3 3 3 Red – Unhealthy‐ 175 Change Cars & truck only 2 1 3 3 3 Change Off Road only 2 4 1 3 3 Change consumer 2 4 3 1 3 products only Change Industry only 2 4 3 3 1 Change 1 4 3 3 3 Energy Sources only 5. Turn all Emission controls to level 1. What is the AQI? Why? 6. Using the reset button, return all Emission controls to the default setting. Turn the Population control to level 1. What is the AQI? Why? (Hint: Click the Population icon and read the information under “What Is This?” in the “Information” box.) Scenario 2: Weather 1. Reset all Emission controls to the default setting. What is the AQI level? 2. Increase only the temperature control to 110 ºF. Check the black sign in the cityscape for the temperature. How does this affect the AQI? Why? 3. Now move the cloud cover to Cloudy (level 3). How does sunlight affect ozone formation? Why? Concluding Questions: Answer the following questions during class discussion; 1. Was there any one variable that seemed to have a greater increase in ozone than others tested? Which one? 2. What steps could be taken to control emissions levels? 3. Can you think of ways to reduce ozone levels? SM‐2 EXPERT GROUP CARDS GROUP 1 What is Tropospheric Ozone? Tropospheric ozone (O3), also known as low‐level ozone, is an air pollutant that is harmful to humans and the natural environment. It is the same O3 molecule as stratospheric ozone. However, since tropospheric ozone occurs where it can be inhaled by humans or enter plant stomata, it can cause damage to our health and vegetation. That is why the phrase “Good up high, bad nearby” is sometimes used to distinguish between the natural stratospheric ozone that protects us from ultraviolet radiation, and the tropospheric ozone that can be a harmful air pollutant. Only about 10% of all atmospheric ozone is in the troposphere, and there is usually no more than 1 molecule of ozone for every 10 million molecules of air near the ground. However, ozone is such a strong pollutant that even those small amounts can be harmful when breathed in to our lungs. Figure 1. Good and bad ozone in the atmosphere. Credit: U.S. EPA : Ozone: Good Up High, Bad Nearby In the previous lesson, we learned how stratospheric ozone forms naturally from oxygen (O2) and UV‐C sunlight. However, in the troposphere, ozone forms as a pollutant when manmade and natural emissions of nitrogen oxides (NOx) and volatile organic compounds (VOCs) react in the presence of sunlight. Unlike other air pollutants, tropospheric ozone is not emitted directly into the atmosphere but instead forms from these other compounds. Details on how those compounds form ground‐level ozone are discussed in another expert card. In Texas, the Houston and Dallas regions have long struggled to meet federal air quality standards for ground‐level ozone. Large amounts of emissions from vehicles and industries (including numerous petrochemical facilities in Houston) and hot weather conditions contribute to ozone pollution. Ozone levels in Houston and Dallas have greatly improved as control devices have been developed to reduce air pollutant emissions from cars and factories. However in spite of the improvement, both cities continue to exceed federal limits. The U.S. Environmental Protection Agency recently lowered the ozone limit from 85 ppb (parts per billion) to 75 ppb, because scientists found that health impacts can occur even at these low levels. This lower limit will make it more challenging for states to reduce emissions sufficiently to meet the ozone standard. SM‐2 EXPERT GROUP CARDS GROUP 2 What are the sources and controls of nitrogen oxide (NOx) emissions? Nitrogen Oxides: Nitrogen oxides (NOx) is a term used to describe two highly reactive gases: nitric oxide (NO) and nitrogen dioxide (NO2). These gases, together with VOCs, contribute to the formation of tropospheric ozone by chemical reactions that are described in a separate group card. Emission Sources: Nitrogen oxides are formed from the combustion of fossil fuels or biomass, and by natural processes such as volcanic eruptions, forest fires, soils, and lightning. It can be seen from Figure 2 that the two leading sources of NOx emissions in the United States are on‐road vehicles (i.e., cars, trucks and buses) and off‐road vehicles and equipment such as construction or agricultural equipment, trains, airplanes, and boats. Electric utilities (“power plants”) and other industries that combust fossil fuels such as coal, oil, and natural gas are also important sources of NOx emissions. Natural emissions of NOx come from lightning, wildfires, and soil. U.S. Nitrogen Oxide Emissions (2008)
Biogenics (Natural)
6%
Industrial Fuel Combustion
8%
Other 10%
On‐road Vehicles
39%
Electric Utilities
17%
Off‐road Vehicles & Equipment
20%
Figure 2. U.S. nitrogen oxide emissions by source category in the US EPA 2008 National Emissions Inventory. Controls: Since most NOx in the atmosphere comes from burning fossil fuels in vehicles, power plants and other industries, one way to control NOx emissions is to use less fossil fuel. This can be done by driving less, using renewable or cleaner burning fuels, driving within the speed limit, maintaining vehicles, and using energy efficient lights and appliances. In addition, government regulations require that new vehicles and power plants emit far less NOx than they did in the past. This has been made possible by the development of many control technologies that strongly reduce NOx emissions from vehicles and other sources. For example, catalytic converters in cars can convert most NOx into harmless nitrogen gas (N2) before the exhaust leaves the tailpipe. Similarly, control technologies for power plants and other industries can sharply reduce the amount of NOx that leaves their smokestacks. Together, these policies have allowed the U.S. to cut NOx emissions by more than 50% since 1980, even as vehicle and electricity use have grown. SM‐2 EXPERT GROUP CARDS GROUP 3 What are the sources and controls of volatile organic compound (VOC) emissions? Volatile Organic Compounds: VOCs are unstable organic compounds that contain carbon. The atmosphere contains hundreds of types of VOCs. When you smell a forest, baking bread, perfume, or many other scents, what you are smelling is VOCs. Some VOCs are harmful to human health, but many others are harmless at typical concentrations in the atmosphere. Together with NOx, VOCs contribute to the formation of tropospheric ozone by chemical reactions that are described in a separate group card. Emission Sources: Figure 3 shows the emission of VOCs to the atmosphere in the United States. The majority of VOC emissions originate from natural biogenic sources, especially trees which emit a VOC called isoprene. However, manmade VOCs can be important contributors to ozone formation in some cities. The biggest category of manmade emissions is evaporation of VOCs from solvents, including paints, cleaning supplies, and other products. VOCs are also emitted when fossil fuels are combusted by on‐road vehicles (i.e., cars, trucks, and buses), off‐road vehicles or equipment (e.g., construction or agricultural equipment, trains, airplanes, and boats), or for other purposes. Some VOCs are also released in the extraction and processing of petroleum and natural gas. U.S. VOC Emissions (2008)
Petroleum & Related Industries
4%
Other
14%
Off‐road Vehicles & Equipment
5%
On‐road Vehicles
6%
Solvents
7%
Biogenics (Natural)
64%
Figure 3. U.S. Emissions of VOCs in the US EPA 2008 National Emissions Inventory. Controls: Regulations and improved technologies have reduced the VOC emissions from paints and other solvents. Catalytic converters and cleaner burning fuels have reduced VOC emissions from vehicles, and other control technologies can reduce emissions from petroleum refineries and other industries. On an individual level, anything we do to reduce our driving and use of solvents can reduce VOC emissions. Biogenic (natural) sources from plants are largely beyond our control; however, trees tend to emit more VOCs on warm and sunny days, so emissions could increase if the climate warms. SM‐2 EXPERT GROUP CARDS GROUP 4 The Chemistry of Tropospheric Ozone Formation How does ozone form in the troposphere? In the previous lesson, we learned how ozone forms naturally in the stratosphere from oxygen and UV‐C sunlight. In the troposphere, ozone instead forms as a pollutant from chemical reactions involving nitrogen oxides (NO and NO2, known collectively as “NOx”), volatile organic compounds (VOCs), and sunlight. Other expert cards describe the emission sources and control technologies for NOx and VOCs. Notice that unlike most other air pollutants, tropospheric ozone is not emitted directly into the atmosphere, but instead forms from these other compounds. Figure 4. Tropospheric ozone (‘bad ozone). Credit: http://www.airnow.gov/index.cfm?action=aqibasics.ozone Since virtually all UV‐C sunlight is absorbed by oxygen molecules (O2) in the stratosphere, almost none of the UV‐C can reach the troposphere to help form ozone. However, most visible sunlight (the portion of the electromagnetic spectrum that our eyes can see) does reach the troposphere. Visible light can break apart nitrogen dioxide (NO2) to form ozone (O3) and nitric oxide (NO), as shown in reaction 1. #1 NO2 + visible light + O2  NO + O3 The NO formed by Equation 1 can react with ozone (O3) or with another radical: #2a NO + O3  NO2 + O2 #2b NO + radical (e.g., HO2)  NO2 + other products Note that if Reaction 1 is followed by Reaction 2a, all of the reactants and products cancel out; in other words, each gas is produced and destroyed one time. Thus, if only Reactions 1 and 2a occurred, ozone could not build up to very high levels in the troposphere. However, if Reaction 1 is followed by Reaction 2b, O3 levels could build up in the troposphere, since the NO2 is replaced without destroying an O3. Notice that these reactions change the form of NOx between NO and NO2, but the overall amount of NOx stays the same. In other words, the NO2 that is lost in Reaction 1 is reproduced by Reaction 2b. This means that NOx serves as a “catalyst” for forming O3 in the troposphere. How do we get the radical needed for Reaction 2b? These radicals form when VOCs react with oxidant gases such as OH (hydroxyl radical) as shown in Reaction 3:
#3 VOC + OH  radical (e.g. HO2) + other product We can summarize how ozone (O3) forms in the troposphere by a single equation: SUMMARY: NOx + VOC + sunlight  O3 Even though ozone formation involves many complicated reactions rather than the simplified equation shown here, this summary reminds us of the three (3) ingredients needed to form ozone (O3) in the troposphere: nitrogen oxides (NOx), volatile organic compounds (VOCs), and sunlight. If any of these ingredients are missing, very little ozone can form. To reduce ozone pollution, we must reduce our emissions of NOx, VOCs or both. .
SM‐2 EXPERT GROUP CARDS GROUP 5 How do weather conditions affect tropospheric ozone formation? In addition to NOx and VOCs, weather conditions or meteorological factors are known to have some influence in the formation of tropospheric ozone. These factors include temperature, humidity, cloud cover and wind direction and speed. Combination of these factors can increase or decrease the amount of ozone in the troposphere. 1. Temperature. Since ozone formation is a photochemical reaction, sunlight has to be present. The heat and light from the sun drive the reactions involved in the formation of ozone molecules. Higher temperatures also increases the evaporation of VOCs into the atmosphere, and causes trees to release more VOCs. For all of these reasons, observational monitors usually measure more ground‐level ozone when temperatures are high. 2. Humidity. Water vapor in the atmosphere helps to form hydroxyl radical (OH), a highly reactive gas that reacts with VOCs to accelerate the formation of tropospheric ozone. However, very humid days may also be cloudy and rainy which can slow down ozone formation. Thus, O3 levels may increase or decrease as humidity changes. 3. Cloud cover. The presence of clouds in the atmosphere blocks some of the sun’s UV and visible radiation. When there are more clouds, less radiation from the sun can reach the ground level. Thus, tropospheric O3 levels tend to be lower on cloudy days. 4. Wind direction and speed. Ozone formation is also influenced by the circulation of air. Wind carries the ingredients necessary for ozone formation from one area of town to another. Fast wind speeds tend to dilute pollution. When air is very calm under an inversion layer, pollution levels can build up. SM‐2 EXPERT GROUP CARDS GROUP 6 What are the negative impacts of tropospheric ozone? Tropospheric or low‐level ozone can have the following health effects, even at concentrations of less than 100 parts per biilion (i.e. 1 ozone molecule for every 10 million air molecules): 1. Make people more sensitive to allergens. 2. Aggravate asthma. 3. Damage and inflame the lungs, making it harder to breathe. 4. Irritate the respiratory system – coughing and irritation in the chest. All of the above conditions can prevent people from taking part in vigorous activities outdoors. Children and the elderly are especially more sensitive to these health effects. In plants, tropospheric or low‐level ozone has been known to enter the plants through their stomata (opening in the leaves for carbon dioxide to enter and oxygen to exit) and damage the cells. This can cause chlorosis in plants (a condition when leaves produce less chlorophyll) and slows down photosynthesis as well as plant growth. In plants that are sensitive to O3, the damage can be seen as brown flecks on the leaves. Ozone damage can reduce crop yields on farms and slow the growth of forests. Figure 5. Snapbeans in clean air (L) and Snapbeans damaged by ozone (R). Credit: Fitzgerald Booker, USDA‐ARS Plant Science Research Unit, North Carolina State University SM‐3 METEOROLOGICAL FACTORS AND OZONE CONCENTRATION Lab Worksheet Directions: Use this worksheet to plan for your investigation. Fill out page 1 and turn it in for approval before conducting the experiment. Use the elements (title, question, hypothesis, etc) in this worksheet in writing the final lab report. Only 1 lab report is required per group. Title of the Investigation: _____________________________________________________________________________________
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_____________________________________________________________________________________ Experimental Site: ___________________________________ Experimental design reviewed and approved on : _______________________ ‐page 1‐ Results and Discussion: Use tables and graphs here. Sample Data Table Meteorological Factor (example: air temperature) Ozone Concentration (ppb) Conclusion: _____________________________________________________________________________________
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_____________________________________________________________________________________ Group Names _______________________________ _______________________________ _______________________________ _______________________________ ‐ page 2‐ SM‐4 CLOUD GUIDE (To help students fill in “Cloud Types” and “Cloud Cover” on Rice Air Curriculum Data Sheets) Cloud Types High in the Sky: Cirrus Middle of the Sky: Cirrocumulus Altocumulus Cirrostratus Altostratus Low in the Sky: Stratus Rain or Snow Producing Clouds: Stratocumulus Cumulus Nimbostratus Cumulonimbus Cloud Cover No Clouds 0% ‐ No clouds Clear <10% Clouds Isolated 10‐25% Clouds Scattered 25‐50% Clouds Broken 50‐90% Clouds Overcast Images:http://www.globe.gov/tctg/atmo_chap.pdf?sectionid=1&lang=EN
SM‐5 The Daily Maximum Eight‐Hour Ozone Averages Summary of Data Make a summary of the ozone values in terms of air quality condition or levels of health concern. Unhealthy Very Good Moderate for Sensitive Unhealthy Unhealthy Hazardous Groups Days For the days, write the date or dates of the month where these AQI are observed. Answer the following questions: 1. Do you see any variation of the ozone level in the area you selected? 2. Which date has the highest ozone level? _______ and which one has the lowest? ________ 3. Explain the possible cause or causes of this variation. 4. What should you do before going out for any outdoor activity? SM‐6 Rice Air Curriculum Ozone and Meteorology Data Sheet Group’s Name : ___________________________________________________________ Measurement location : ____________________________________________________ Please choose three places where you will measure surface temperature (circle
one for each):
Surface Temperature #1: Grass Barren Land Shrubs Concrete Asphalt Other: ____________________ Surface Temperature #2: Grass Barren Land Shrubs Concrete Asphalt Other: ____________________ Surface Temperature #3: Grass Barren Land Shrubs Concrete Asphalt Other: ____________________ Day 1 Day2 Day 3 Day 4 Day 5 Date Day of Week Beginning of class (ozone strip exposed) Time (hour:min) Wind direction Air temperature (°C) Surface temperature (°C) Relative Humidity (%) End of class (ozone strip read) Time (hour:min) Wind direction Air temperature (°C) Surface temperature (°C) Relative Humidity (%) Cloud Types (see Cloud Guide; ; List all types seen) Cloud Cover Ozone concentration (parts per billion) AQI SM‐7 EVALUATION Direction: Write at least a 1‐page essay on the following prompt: Houston is one of the cities in the U.S. that exceeded the ozone standard. As an individual and resident of Houston, how can you help reduce the ozone concentration around the area? What steps should you take and how would these steps impact the environment? …………………………………………………………………………………………………………………………………………………………………
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