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Study of adaptations of city flora to smog

Study of adaptations of city flora to smog

Introduction: (Initial Observation)

Harmful effects of smog on human and other animals is well known. Smog in many cases has resulted death and serious illness with symptoms such as aching lungs, wheezing, coughing, and headaches. While smog has serious harmful effects on animals, we are not sure how it affects other organisms especially plants.

In this project you will design and perform experiments to discover the effect of smog on plants. You may also gather information or study on plants that exist in polluted areas and compare them with similar plants in clean air.


If you have any questions, click on the help button at the top of this page to send me your questions. I may respond by email, but often I update this page with the information that you need.

Project Advisor

Information Gathering:

Find out about smog. Read books, magazines or ask professionals who might know in order to learn about the effects of smog on plants. Keep track of where you got your information from.

The following are samples of information that you may find.

The expression “smog” was first used in “Turn-of-the-Century” London to describe a combination of “smoke” and “fog”. Smog occurred when water vapor in the air condensed on small particles of soot in the air, forming small smog droplets. Thousands of Londoners died of pneumonia-like diseases due to the poisonous air.

Today, smog is usually produced photo chemically, when chemical pollutants in the air (notably nitrogen oxides and volatile organic compounds (VOC’s) from automobile exhausts) are baked by the sun and react chemically. Ground-level ozone is produced by a combination of pollutants from many sources such as automobile exhausts, smokestacks, and fumes (VOC’s) from chemical solvents like paint thinner or pesticides. When these smog-forming pollutants (called “precursors”) are released into the air, they undergo chemical transformations and produce smog. Weather conditions, such as the lack of wind or a “thermal inversion”, also cause smog to be trapped over a particular area.

Smog causes health problems such as difficulty in breathing, asthma, reduced resistance to lung infections, colds, and eye irritation. The ozone in smog also can damage plants and trees, and the haze reduces visibility. This is particularly noticeable from mountains and other beautiful vistas such as National Parks.

Severe smog and ground-level ozone problems exist in many major cities, including much of California from San Francisco to San Diego, the mid-Atlantic seaboard from Washington, DC to southern Maine, and over most major cities of the South and Midwest.

Smog City is an interactive air pollution simulator that shows how environmental factors and land-use contribute to air pollution. Click here to access smog city.

What is ozone ?

Ozone is a molecule composed of three atoms of oxygen. Two atoms of oxygen form the basic oxygen molecule–the oxygen we breathe that is essential to life. The third oxygen atom can detach from the ozone molecule, and re-attach to molecules of other substances, thereby altering their chemical composition. Ozone is a gas. It is generally represented as O3.

How is ozone produced ?

In the atmosphere, by lightning actuating on oxygen. Then, Oxygen (two atoms), is transformed in Ozone (three atoms).

Some Devices, (ozone Generators), produce Ozone “on site”, by using high voltage (corona effect), and transform oxygen into ozone, by adding an extra atom. Ozone is not stored or carried as chlorine.

Other devices, produce Ozone by using UV (Ultra Violet) systems, but they are not so effective as Generators.

Ozone is a word that comes from Greek : Ozein = smell.

Ozone is the most powerful oxidant for water treatment, and disinfections process, especially for the food and beverage industry. It is environmental friendly, and FDA (Food and Drugs Administration – USA), classifies Ozone as GRAS (Generally Recognized As Safe).

What is smog?

Smog is a distinct form of poor air quality. It occurs on warm summer days when a combination of toxic gases and fine particles forms through a series of chemical reactions triggered by sunlight and heat. Each summer, Toronto experiences a number of ‘smog episodes” or ‘smog days” on which air quality falls well below acceptable health standards.

Where does smog come from?

The chemicals that make up smog come from many sources:

  • Nitrogen oxides (NOx): in Ontario the major source is gasoline-powered vehicles (about 66%). Much of the rest is from industrial combustion processes, such as power generation, smelters, primary metal processing.
  • Volatile Organic Compounds (VOCs): from evaporation of gasoline, oil-based paint and cleaning solvents. The major source is gasoline.
  • Carbon Monoxide: a major pollutant in Toronto — 93% of which comes from motor vehicles.
  • SULFUR Dioxide: vehicles especially diesel, electrical power plants.
  • Suspended particulates (particles): from vehicle emissions (38%) and residential heating, such as wood burning. Diesel is a major source of particles.


Riverside scientists were the first to determine that this sick plant syndrome was not caused by known industrial pollutants, but by “secondary” air pollutants, namely ozone and other photochemical oxidants.


Ozone (O3) in the troposphere causes more damage to plants than all other air pollutants combined.


The same chemical properties that allow high concentrations of ozone to react with organic material outside the body give it the ability to react with similar organic material that makes up the body, and potentially cause harmful health consequences. When inhaled, ozone can damage the lungs. Relatively low amounts can cause chest pain, coughing, shortness of breath, and, throat irritation. Ozone may also worsen chronic respiratory diseases such as asthma and compromise the ability of the body to fight respiratory infections.



Open-topped chambers constructed for ozone research at University of California. Since ozone is heavier than oxygen, it does not exit the top opening. On the other hand top opening allows the needed carbon dioxide to enter the chamber.

Project Advisor

Picture Source…

Question/ Purpose:

What do you want to find out? Write a statement that describes what you want to do. Use your observations and questions to write the statement.

The purpose of this project is to find out how smog affects plants or vegetations in an area. Can plants adapt to smog caused by cars, industries, and use of fossil based fuels.

Research Plan:

Before you start any research project, you must have a plan. What do you want to do in your investigation. This is a sample plan:

  1. Search the Internet for previous studies or reports.
  2. Search local library for related books or publications.
  3. Visiting a large (and polluted) town and its surrounding area to see the variation of plant species as we get away from the town.
  4. Performing plant growth experiments to see how smog pollutants affect the plant.

Identify Variables:

When you think you know what variables may be involved, think about ways to change one at a time. If you change more than one at a time, you will not know what variable is causing your observation. Sometimes variables are linked and work together to cause something. At first, try to choose variables that you think act independently of each other.

Smog is a collection of smoke, gases, and vapors that may also include other chemicals such as ozone formed by photochemical reactions caused by sunlight. We can test the effect of each of such variables separately. For example if we want to test the effect of smoke on plants, variables will be defined as follows:

  • Independent variable is the smoke. (possible values are none, low and high)
  • Dependent variables are plant growth and health.
  • Controlled variables are all other environmental factors that may affect plant growth and health including soil, nutrients, water, light, air, and temperature.

If you want to test any other variable, then that variable will become your independent variable (also known as manipulated variable). For example, if you want to test the effect of ozone on plants, then ozone will be your independent variable. Possible values are (presence and absence) or (none, low, high).


Based on your gathered information, make an educated guess about what types of things affect the system you are working with. Identifying variables is necessary before you can make a hypothesis.

The following is a sample hypothesis:

Smoke is caused by burning fossil base fuels and other organic material. Such burning also produces large amounts of carbon dioxide that is needed for plants to grow. For this reason I believe smoke does not hurt plants and if it does not include other particle pollutants, it may even help plants grow better.

Experiment Design:

Design an experiment to test each hypothesis. Make a step-by-step list of what you will do to answer each question. This list is called an experimental procedure. For an experiment to give answers you can trust, it must have a “control.” A control is an additional experimental trial or run. It is a separate experiment, done exactly like the others. The only difference is that no experimental variables are changed. A control is a neutral “reference point” for comparison that allows you to see what changing a variable does by comparing it to not changing anything. Dependable controls are sometimes very hard to develop. They can be the hardest part of a project. Without a control you cannot be sure that changing the variable causes your observations. A series of experiments that includes a control is called a “controlled experiment.”

Experiment 1: Simulate smog

Introduction: You will perform an experiment in which you will create artificial “smog” in a jar. Make sure that you understand that the jar is only a model, and models by nature are limited. For example, the purpose of this model is to illustrate the appearance and behavior of smog, not the composition or effects. It is important to understand that smog is not just a “smoky fog”, but a specific phenomenon (known as temperature inversion).


  1. Cut a strip of paper about 6 inches by 2 inches. Fold the strip in half and twist it into a rope.
  2. Make a snug lid for the jar out of a piece of aluminum foil. Shape a small depression in the foil lid to keep the ice cubes from sliding off. Carefully remove the foil and set it aside.
  3. Put some water in the jar and swish it around to wet all the insides of the jar. Pour out the extra water.
  4. Light the paper “rope” with a match and drop it and the match into the damp jar. Put the foil lid back on the jar and seal it tightly. Put ice cubes on the lid to make it cold. (The ice cubes will make the water vapor in the jar condense.) You must do this step very quickly, perhaps with some assistance.

TAKE NOTE! Be careful to have an adult supervise while using matches. DO NOT let anyone breathe the “smog” produced in the experiment, and when the experiment is completed, be sure to release the “smog” outside.

5. Describe what you see in the jar. How is this like real smog? What conditions in the jar produced “smog”? (Moisture plus soot particles from the burning matches plus carbon dioxide and other solvent vapors.)

6. Have you ever seen smog (not fog)? Have you ever breathed air outside that smelled funny?

Experiment 2: Effect of smoke on plants


Yong plants are perfect choices for testing the effect of different factors on plants. You may purchase identical and same age young plants from a local nursery; however, I recommend to start from planting your own seeds. Different seeds such as tomato, cucumber, radish and many more are available from nurseries. Before purchasing, read the package and check the germination time to make sure that they grow fast enough for your experiment.

Plant seeds 3/8 to 1/2 inch deep in lightweight, sterile potting mix. You can plant closely in shallow containers, then transplant the seedlings to larger containers or small individual pots when they have their first set of true leaves; or you can plant seeds about 2 inches apart in deeper (at least 3-inch-deep) pots and let them flower without transplanting. Start your actual experiment when you have at least 10 young plants in 10 different pots. If you are transplanting, do not start your experiment until about 3 days after transplanting. Some plants may get damaged during transplanting and die. You must only use healthy plants for your experiment. I suggest to start with about 20 plants and select 10 of healthy plants for your experiment.

Warning: Part of this experiment involves open flame. It needs adult supervision and it must be performed outdoors, away from buildings and flammable material.


  • Make two wooden or metal cubic frames about 2′ x 2′ x2′ and cover them with clear plastics and use them as growth chambers. They don’t really have to be cubic. Also they are not air sealed. You will use them like a dome over your plants.
  • Label five of your plants as “AIR” and five others as “SMOKE”
  • Label one of the chambers as “AIR” and the others as “SMOKE”
  • Place all plants labeled “AIR” in “AIR” chamber and all plants labeled “SMOKE” in “SMOKE” chamber.
  • Place a small metal or ceramic container under the “smoke” chamber away from the sides and close to the center.
  • Make a smoking oil by mixing small amounts of diesel fuel, motor oil and rubbing alcohol (equal amounts of each).
  • Get a piece of cotton rope or similar cotton piece about the size of a sugar cube and wet it by smoking oil.
  • Place the piece in the center of the metal container and us a utility lighter or a match to light it up. This is the risky part. If the flame is too high, too hot or too close to the plastic, it will melt or burn your plastic chamber. If this happens, you will need to make an aluminum tripod to cover the flame from the top.
  • At this time one of your chambers has smoke and the other has clean air. make daily observations and water the plants (same amount for all plants).
  • Repeat smoke making procedure every day after you water the plants.
  • After 2 to 3 weeks, compare the plants in “AIR” chamber with plants in “SMOKE” chamber. Compare plant height, number of leafs, size of leafs, color of leafs and general health of plants. Record your results in a table like this:

Plants in group “AIR”

Plant Number Height Number of leaves Area of largest leaf Color of leaves


Plants in group “SMOKE”

Plant Number Height Number of leaves Area of largest leaf Color of leaves

You may use the results in these tables to draw a bar graph. For example, one bar may show the average height of plants in “SMOKE” group and another bar may show the average of height of plants in “AIR” group. Other graphs may be made for number of leaves or area of leaves.

Experiment 3: Effect of ozone on plants


Gathered information claim that ozone is the only part of smog that is harmful to plants. If you have access to ozone generators, you may perform this experiment.


This experiment is very similar to experiment number 2. The only difference is that instead of a smoke generator, you will use an ozone generator.

Ozone generators sell for a few hundred dollars each. Recently I saw an ozone generator offered on EBAY.com for $40.00 (new, from china). If you don’t have access to ozone generator, don’t do this experiment.

More Experiments:

Smog and smoke also leave a layer of oily substance on plants. In other words evaporated oil condense on plant leaves. You may do a similar experiment by spraying or rubbing some motor oil on plant leaves and see how this oil affects plants.

Other Methods:

Another method that scientists use to study the effects of urban or industrial pollutants on plants is making observations and recordings of existing plants, especially wild plants that grow naturally. Gathered information may show that certain species have disappeared from polluted areas while some other species are well adapted and continue to grow. This process takes more time and requires many hours of observations and recording.

Materials and Equipment:

List of material can be extracted from the experiment section.

Results of Experiment (Observation):

Experiments are often done in series. A series of experiments can be done by changing one variable a different amount each time. A series of experiments is made up of separate experimental “runs.” During each run you make a measurement of how much the variable affected the system under study. For each run, a different amount of change in the variable is used. This produces a different amount of response in the system. You measure this response, or record data, in a table for this purpose. This is considered “raw data” since it has not been processed or interpreted yet. When raw data gets processed mathematically, for example, it becomes results.


While comparing plants in two groups, you will need to calculate average height and average number of leaves in each group.

Summary of Results:

Summarize what happened. This can be in the form of a table of processed numerical data, or graphs. It could also be a written statement of what occurred during experiments.

It is from calculations using recorded data that tables and graphs are made. Studying tables and graphs, we can see trends that tell us how different variables cause our observations. Based on these trends, we can draw conclusions about the system under study. These conclusions help us confirm or deny our original hypothesis. Often, mathematical equations can be made from graphs. These equations allow us to predict how a change will affect the system without the need to do additional experiments. Advanced levels of experimental science rely heavily on graphical and mathematical analysis of data. At this level, science becomes even more interesting and powerful.


Using the trends in your experimental data and your experimental observations, try to answer your original questions. Is your hypothesis correct? Now is the time to pull together what happened, and assess the experiments you did.

Related Questions & Answers:

What you have learned may allow you to answer other questions. Many questions are related. Several new questions may have occurred to you while doing experiments. You may now be able to understand or verify things that you discovered when gathering information for the project. Questions lead to more questions, which lead to additional hypothesis that need to be tested.

Possible Errors:

If you did not observe anything different than what happened with your control, the variable you changed may not affect the system you are investigating. If you did not observe a consistent, reproducible trend in your series of experimental runs there may be experimental errors affecting your results. The first thing to check is how you are making your measurements. Is the measurement method questionable or unreliable? Maybe you are reading a scale incorrectly, or maybe the measuring instrument is working erratically.

If you determine that experimental errors are influencing your results, carefully rethink the design of your experiments. Review each step of the procedure to find sources of potential errors. If possible, have a scientist review the procedure with you. Sometimes the designer of an experiment can miss the obvious.


List of References


Bailey, Donna. What Can We Do About Noise and Fumes. New York: Franklin Watts (1991).

Baines, John. Exploring: Humans and the Environment. Austin, TX: Steck-Vaughn Company (1993).

Easterbrook, Gregg. “Winning the War on Smog.” Newsweek, 122 (23 August 1993) p.29.

Krupnick, Alan J., and Paul R. Portney. “Controlling Urban Air Pollution: A Benefit-Cost Assessment.” Science, 252 (26 April 1991). p.522.

Pasternak, Judy. “Long-Term Lung Damage Linked to Air Pollution; Respiratory Deterioration Is Found in Areas Where Air is Dirtiest.” Los Angeles Times, (29 March 1991) p. A1.