This lesson provides an introduction to the problems associated with ground-level ozone ('smog'). It reinforces the idea that ozone at ground level is harmful while that in the upper atmosphere has a beneficial effect. There is also discussion about how ozone is formed and some of its effects on air quality and human health. Students can listen to two National Publc Radio (NPR) shows that discuss air pollution in Los Angeles and Houston, and perform an activity in which they use an online simulation to change various parameters (weather conditions, population, emission levels from various sources) and observe the changes in air quality that result. Educational levels: Undergraduate lower division, High school

Matt Laposata

English

Digital Library for Earth System Education

 
 Ground-level Ozone: Smog City 
 
 
Table of Contents: 
(1.) Smog 
(2.) Forming Ground-level Ozone 
(3.) Effects of Ozone on Air Quality and Human Health 
(4.) Activity: Smog City  
 
Smog 
 
In this exercise we will be examining ground-level ozone, commonly referred 
to as "smog" ("smoke" + "fog" = "smog"). Smog is formed by the combination 
of air pollutants and sunlight, and can have adverse effects on humans and 
other organisms. You have likely heard of ozone in a different capacity.  
Ozone also occurs high above the earth's surface in the stratosphere, where 
it serves a protective function by blocking harmful ultraviolet radiation from 
the sun.  The ozone in each case is the same molecule (three bound oxygen   
atoms), but in one location (high in the atmosphere) it is beneficial to living things, and at 
another location (ground-level) is harmful.  Realizing these "two faces" of ozone is important 
before proceeding, so look over the brochure below from the U.S. Environmental Protection 
Agency. 
 
 
Ozone: Good Up High, Bad Nearby 
Compares and contrasts ozone in stratosphere and troposphere 
U.S. Environmental Protection Agency 
http://www.epa.gov/oar/oaqps/gooduphigh/ 
 
   
 
Listen 
Topic: L.A. Smog 
Date: December 26, 2000 
Summary: NPR's Ina Jaffe reports that while the average weekday 
in Los Angeles brings traffic jams throughout the city and region, 
the air pollution is at its worst during the weekend. Scientists say 
the reasons for this are as hazy as the LA skyline 
(http://www.npr.org). (3:43) 
Link: http://www.npr.org/ramfiles/me/20001226.me.11.ram 
Requires RealPlayer 
 
Ground-level Ozone: Smog City 1 
 
Listen 
Topic: Houston Smog 
Date: September 10, 2001 
Summary: NPR's John Burnett reports on Houston's air pollution 
problem. Though Houston has the worst ground-level ozone in the 
country, business leaders have remained reluctant to tighten their 
emissions standards. But now these leaders are becoming more 
open to change, as they realize that Houston's reputation for poor 
air quality is making it harder to attract new businesses and 
talented employees (http://www.npr.org). (8:39)  
Link: http://www.npr.org/ramfiles/me/20010910.me.13.ram 
Requires RealPlayer 
 
 
Forming Ground-Level Ozone  
 
In this exercise we will be looking exclusively at ground-level ozone, also known as 
photochemical smog. The first step is for you to understand how photochemical smog is formed.  
View the animation below from the U.S. EPA and the Pima County (AZ) Department of 
Environmental Quality to learn about the process.  When prompted, click the "Make Ozone" icon 
to continue the animation. 
 
 
How Ozone is Formed 
Animation shows process of smog formation 
U.S. Environmental Protection Agency 
http://www.airinfonow.org/html/makingozone/o3play.htm 
Requires Macromedia Flash Player 
 
 
Although visually appealing, this is a simplistic view of ozone formation. The actual process by 
which ozone forms and stays trapped at the surface is more complex. To examine this in 
greater depth, view material at the site below. 
 
 
Thermal Inversions and Photochemical Smog 
In-depth descriptions of smog formation and concentration with thermal inversions 
The California Environment 
http://daphne.palomar.edu/calenvironment/smog.htm 
 
 
Effects of Ozone on Air Quality and Human Health 
 
After reviewing this information, you should have a good understanding of the process by which 
ozone forms near the surface and how it can remain trapped there. But what does it do to you? 
As you would expect, ozone's effects occur primarily through the respiratory system. Let's 
examine the functioning of the human respiratory system with another Flash animation from the 
EPA-Pima County site. First view the "Normal Breathing" animation and then examine how 
ozone affects respiration.  View the other pollutants and compare and contrast their effects with 
those of ozone. 
 
Ground-level Ozone: Smog City 2 
 
Lung Attack 
Animation of smog's effects on the human respiratory system 
U.S. Environmental Protection Agency 
http://www.airinfonow.org/html/lungattack/lungplay.htm 
Requires Macromedia Flash Player 
 
 
Finally, let's take a more comprehensive look at the effects of smog on humans, and on the 
mechanisms used to alert individuals to air quality issues. Review the EPA publication "Smog - 
Who Does It Hurt?" at the link below. 
 
 
Smog – Who Does It Hurt? (PDF) (819 KB) 
Smog's effects on humans 
U.S. Environmental Protection Agency 
http://www.epa.gov/airnow/health/smog.pdf 
 
 
Activity: Smog City  
 
There exists on the Internet an exceptional simulation of the factors involved in smog formation - 
Smog City. The simulation was produced by the Sacramento Metropolitan Air Quality 
Management District and allows users to change various parameters and observe the changes 
in air quality that result. The site has several pages with useful, concise information regarding 
the simulation, so comprehensive directions are not required.   
 
 
Smog City 
Interactive simulation of ground-level ozone formation 
Sacramento Metropolitan Air Quality Management District 
http://www.smogcity.com/welcome.htm 
  
 
Weather Conditions 
 
(1.) Review the following sections in order listed: Home, Visitors Tour Guide, Smog City 
Science, Help, and What You'll Learn. 
(2.) After learning how to run the simulation, choose Run Smog City. 
(3.) Follow the directions provided on the activity sheet. 
 
 
Ground-level Ozone: Smog City 3 
Graphing  
 
In the first section of the Activity Sheet, you are asked to graph two smog profiles on one chart. 
Do this by distinguishing between the lines with different colors, or by drawing two different 
types of lines (dashed line vs. solid line). Make sure the reader is easily able to distinguish 
which line is which by adding a label to the chart identifying each line. An example is provided in 
Figure 1. 
  
 
 
 
Figure 1. Graphing two smog profiles on one chart 
  
 
Interpreting Ozone Profiles 
 
When interpreting the severity of the ozone profiles the simulation returns, you must look at two 
characteristics. First, you should evaluate the maximum ozone concentration attained during the 
day, and the corresponding air quality level. If you change a parameter and the air quality 
reading goes from Moderate to Unhealthy, this represents a significant reduction in air quality. 
Second, you should also evaluate the length of time spent at different ozone levels. This is best 
exemplified by Figure 2, which shows two runs that both have peak ozone levels at the upper 
portion of the Unhealthy level. Note though, that in the second curve, air quality is at the upper 
portion of the Unhealthy range throughout the entire afternoon (note plateau shape of curve), 
while in the first curve the air quality is in the Unhealthy range for a much shorter period of time 
(note peak shape of curve). This has obvious implications for the individuals breathing the air, 
as adverse effects are dependent not only on the severity of exposure (the maximum ozone 
level attained), but also on the length of time individuals are exposed to these conditions (the 
shape of the curve). 
  
 
 
 
 
Figure 2. Comparing peak ozone concentrations and exposure durations 
  
Ground-level Ozone: Smog City 4 
 
Pollutant Outputs 
 
(1.) Note that the factors we've examined so far aren't the only ones modeled in Smog City. 
The simulation also allows you to manipulate the sources of the compounds that form 
ozone, and this is done with the controls at the bottom of the screen. You can change the 
population size of your city, as well as pollutant inputs from passenger vehicles, off-road 
vehicles, industry, and consumer products. Follow the directions on the Activity Sheet to 
evaluate these outputs. 
(2.) While the weather conditions that affect smog formation are beyond human control, the 
release of the compounds that cause ozone formation is not. Model some approaches to 
reducing smog concentrations in Smog City by altering some factors we realistically could 
control, and observing the resultant changes in air quality with the simulation. Complete 
the exercise described on your Activity Sheet. 
 
 
Ground-level Ozone: Smog City 5 
  
ESA 21: Environmental Science Activities Activity Sheet  Ground-Level Ozone  
 
Name: 
 
Lecture Professor: 
 
Examining Weather Factors: 
For each of the following, vary only the parameter listed - keep the rest on the default setting.  
Make sure you hit the Reset button after each run to ensure the settings are returned to the 
default before the next run.  For all of the charts except the Default, put both of the profiles (e.g. 
80o F and 120o F) on the same chart, identifying each curve with a label and a different line type 
(solid line or dotted line) or color (red line or blue line). 
 
Defaults: 
100o F  
Mild Inversion 
Light wind 
Partly cloudy 
 
 
Temperature: 
(a.) 80o F  
(b.) 120o F 
 
 
Inversion: 
(a.) No inversion 
(b.) Strong 
inversion  
(lowest box) 
 
 
Wind Speed: 
(a.) No wind  
(b.) Max wind 
 
 
Sunlight: 
(a.) Cloudy skies 
(b.) Full sun 
 
Ground-level Ozone: Smog City 1 
 Evaluating the Factors: 
Through your runs you’ve seen that some of these factors have a greater effect on ozone levels 
than others.  List the four factors from most important to least important in the space below, and 
explain why you listed them in the order you did.  
 
 Most important -----------------------------------------------------------  Least important 
 
 
 
 
 
 
 
The Ultimate Bad Smog Situation: 
Describe the settings for each factor, and sketch the smog profile in the space below. 
 
 Temperature Inversion Layer Wind Speed Sunlight 
Setting  
 
   
 
 
 
 
Examining the Sources of Pollutants: 
Toggle the dials at the bottom of the page and observe how they affect the bar graph showing 
the relative contributions of the four different sources of pollutants.  Once you’ve done this, 
increase or decrease the population, and see how the magnitude of the outputs are changed 
with greater or fewer people.  Rank the four categories (dials) from greatest to least contributor, 
and describe the effects of population on pollutant outputs.    
 
 
Greatest contributor -----------------------------------------------------------  Least contributor 
 
 
 
 
 
 
 
 
 
 
 
 
 
Ground-level Ozone: Smog City 2 
 Ground-level Ozone: Smog City 3 
The Value of Simulations: 
Smog City is in trouble.  True to its name, it has routinely exceeded federal air quality standards, 
and the city must take immediate steps to improve air quality.  For the sake of this exercise, we 
will use the default settings as the current situation in Smog City (hitting Reset will restore these 
settings as before).  Two competing proposals are on the table for improving air quality.  Use 
the simulation to evaluate each one. 
 
Proposal 1: The city develops a comprehensive mass transit system that reduces the number of 
passenger vehicles by developing a subway-rail system to ferry commuters around the city.  
This would reduce the Cars and Truck dial to its lowest setting, but increase the Off Road dial 
to its maximum setting.   
 
Proposal 2: The city enacts a comprehensive plan that addresses pollution from multiple 
sources.  The city’s subway-rail system is modestly improved, and major initiatives are 
undertaken to reduce pollutant outputs from Industry and Consumer Products.  This would 
reduce the Cars and Truck, Industry, and Consumer Products dials by one increment each, 
and increase the Off Road dial by one increment.    
 
Run the simulations with the default weather conditions, show the profiles for each below, and 
make a recommendation to the city council on which proposal to adopt, providing justification for 
your answer.  Be sure to address both maximum pollutant levels and length of exposure.   
 
Proposal 1: 
Cars -2 
Off Road +2 
 
 
Proposal 2: 
Cars -1 
Off Road +1 
Industry -1 
Consumer -1 
 
 
Recommendation and Justification: 
 
  
 


Ground-Level Ozone: Smog City

http://esa21.kennesaw.edu/activities/smog-city/smog-city.pdf

Ground-Level Ozone: Smog City

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