MCTP Maryland Collaborative for Teacher Preparation The Air We Breathe: Is Dilution the Solution to Pollution? Thomas C. O'Haver Department of Chemistry and Biochemistry University of Maryland College Park, MD 20742 (301) 4051831 to2@umail.umd.edu NSF Cooperative Agreement No. DUE 9255745 Topic The atmosphere; air quality and pollution. Primary Expected Outcomes The student should be able to identify the general regions of the atmosphere with respect to altitude and the relationship of air pressure to altitude; recognize the composition of air and reasons for local and regional variations in air composition; understand factors behind air quality and the chief components of air pollution; interpret air quality data in terms of concentrations units and pollution levels, including the unreasonableness of totally "pollution-free" levels; use scientific notation and significant figures in performing basic calculations; differentiate among elements, compounds, and mixtures; understand the differences between atoms and molecules, between symbols for elements and formulas for chemical compounds; write and interpret simple chemical formulas and balanced equations; name selected chemical elements and compounds; describe the involvement of automobile emissions with photochemical smog and other forms of air pollution; evaluate conditions significant in risk/benefit analysis; describe the nature of air quality policies in this country and abroad in terms of effectiveness of air pollution control. Scientific and/or Math Concepts AAAS benchmarks: Physical Setting: 4B The Earth; 4D The Structure of Matter; Habits of Mind: 12B Estimation and Computation; 12C Manipulation and Observation. Disciplines integrated Earth science, chemistry, mathematics. Prerequisite knowledge Basic arithmetic with decimal numbers; exponents; percents; fractions; area and volume. Student's Preconceptions From the AAAS Benchmarks: Students of all ages ... lack an appreciation of the very small size of particles. Multicultural aspects Air quality is an important aspect of global interdependence (AAAS Benchmarks: Human Society 7G) that couples all nations large and small and has been a source of considerable social conflict between the industrial nations and developing nations. Activities and Experiences 1. Student share personal experiences of the change of air pressure with altitude (e.g. popping ears, air travel, boiling eggs in Denver, etc). Discussion: Why does atmospheric pressure decrease with altitude? 2. Student share personal experiences of variation in local air quality (visibility; lung irritation, etc.). What are the normal components of air and what is components are pollutants? 3. Review of some basic concepts: elements, compounds, simple chemical formulas, combustion reactions, conservation of mass. 4. What creates most of the air pollution? Students who drive cars are asked to bring in their last auto emissions test ticket. Results are collected, interpreted, compared to the current National Ambient Air Quality Standards. The units of measurement used on the ticket (e.g. ppm) are discussed and related to percent and to molecules per liter. 5. Is air pollution getting better or worse? Class looks at and interprets Environmental Protection Agency data on major air pollutants for selected cities in the U.S. and changes in average concentrations over the last two decades. Discuss trends. 6. How big is the atmosphere? Class looks at some typical textbook drawings of the earth and its atmosphere. Using data in the book, students attempt to draw a scale model of the earth and the atmosphere on a plain piece of paper, representing the earth as a large circle and the atmosphere as an enclosing concentric circle. (Students discover that this is impossible to draw, since most of the atmosphere lies in a layer that is 1/1000th the radius of the earth. The typical textbook drawings are discovered to be wrong - not to scale). 7. Challenge question: Is dilution the solution to pollution? If I took one liter of a toxic but otherwise stable substance and released it into the outside air and waited until it is completely mixed with the entire atmosphere of the earth, what would be the concentration of the substance expressed in ppm by volume? How does that compare to the ambient air quality standards? Map out a strategy for estimation. How could we estimate the total volume of the atmosphere in liters? What assumptions are reasonable (earth is a sphere; atmosphere is a spherical shell). Look up equation for volume of a sphere. Decide on a way to estimate the average thickness of the atmosphere based on a plot of air pressure vs altitude. Perform calculation and units conversion using a calculator or spreadsheet. Help students with exponential notation as needed. How many molecules of that substance would I breathe in each breath of air for the rest of my life? How can the concentration expressed in ppm seem so low but the number of molecules in a breath seem so large? Do they not express the same concentration? Student handouts -------------------------------------------------------------------- Chemistry 121/122 Name________________________________ Chapter 1: The Air We Breathe This is not a quiz, but rather a class exercise. The papers will be collected and graded. You may talk to your classmates, but you must write your own person answers to each question. 1. List the air pollutants that are discussed in Chapter 1 (give the names or chemical formulas). 2. Of the air pollutants listed on page 8 of the textbook, which do you think is the most hazardous? 3. a. On the basis of the data on page 15, would you say that air pollution has been getting better or worse since 1975? b. Which air pollutant has had the largest change since 1975? c. What do you think is the largest source of this pollutant? d. Why do you think this pollutant has decreased so much since 1975? e. Why were lead compounds (e.g. tetraethyl lead) added to most gasoline that was sold before 1975? f. Why do you think that the gas companies were able to "get away" with adding lead - a substance that has been known to be toxic for many years? In other words, why was there not a public outcry from the very beginning? 4. a. Some copies of recent Maryland Vehicle Emission Test Reports are being circulated around the class. Look at these and list the pollutants that are measured here (HC = hydrocarbons). b. Convert the test reading for carbon monoxide (CO) on the test ticket from percent (PCT = percent) to PPM (parts per million). c. How does the test reading for CO compare to the permissible limit for CO listed on page 8 of the textbook? d. How can the car pass the test when the CO emission is so much greater than the permissible limit? 5. As you know, normal (clean) air is composed of mostly nitrogen and oxygen. One of the most toxic air pollutants (Table 1.2) is nitrogen oxide, which from the name is also composed of nitrogen and oxygen. What is the difference between nitrogen oxide and the nitrogen and oxygen in normal air that would account for the toxicity of nitrogen oxide? 6. Look at the textbook drawings of the earth and its atmosphere on pages 54 and 64 of the textbook. Using the data in the textbook, draw a scale model of the earth and the atmosphere on the back of this paper, representing the earth as a large circle and the atmosphere as an enclosing concentric circle. Rulers and compasses are available for your use. Based only your experience, what can you say about the accuracy of the scale of the drawings on pages 54 and 64? 7. Consider the following hypothetical experiment. Suppose you were to take one liter (12 liter = 1000 cubic centimeters) of a toxic but otherwise stable gas and release it into the outside air and waited until it is completely mixed with the entire atmosphere of the earth, what would be the concentration of the substance expressed in ppm by volume? a.Without actually performing this calculation, what other piece of information would you have to know to obtain the solution of this problem? b. If you were to look up the formula for the volume of a sphere, and supposing that you had a number for the "thickness" of the atmosphere, how could you estimate the volume of the atmosphere? c. How could you estimate the "thickness" of the atmosphere? Does the atmosphere have a sharp upper boundary? Based on Figure 1.2 (page 6), what value for the thickness of the atmosphere would you personally use for your calculation? Why? d. What would you guess is the probability that one molecule of that toxic substance substance, after it is completely mixed with the entire atmosphere of the earth, would be found in one breath of air? e. The accepted value for the number of molecules in one liter of air at atmospheric pressure is given by the book (page 21) as 2 X 1022 molecules. If you accept this number, and assuming that you were able to calculate the volume of the entire atmosphere in liters, how could you actually calculate the number of molecules of your hypothetical toxic substance in one liter of air? You needn't actually do the calculation, just explain how you would do it. -------------------------------------------------------------------] Bibliography American Chemical Society, "Chemistry in Context: Applying Chemistry to Society", Wm. C. Brown Publishers, 1994.