Lab 2—Air Pollution and Vegetation

In this exercise, you will determine the effects of air pollution on vegetation.

Elevated levels of air pollution are found near major roads. Vehicle exhaust can include carbon monoxide, NOx (oxides of nitrogen), and

particulates (e.g., soot). These pollutants can have negative effects on vegetation. Air pollution diminishes with increasing distance from

a major road.

In this experiment, the independent variable is the distance from the road. The dependent variable is the health of plants. But how does

one measure plant health? One way to do this is to look at the leaves. Does a healthy plant have smaller or larger leaves? How could you

measure the size of the leaves or needles?

Instructions

Design your experiment according to the following parameters:
Find appropriate sampling sites, including a site that is close to a major, busy road, and two sites that are at increasing distances from

the road. The exact distance is not critical, but the suggested range of sites is 10–100 metres from the road. Site A is closest to the

road; site B is farther away from the road; site C is farthest away from the road.
Determine the species of plant you will measure. Individual plants of the same species must be located at different distances from the

road.
Determine a parameter for measuring the size of the leaves or needles. For example, length, width, or mass could be used.
Randomly collect 20 leaves or needles from the same species of plant at each sampling site. You don’t have to collect all the samples from

the same plant. Keep the samples from each site in separate containers (small, transparent plastic bags are good for this), and label each

container with a permanent marker.
Note: You will need to use some judgment here. For example, don’t remove vegetation samples from plants on other people’s property without

permission.
Take digital photos of each site, to include in your report.
Measure the size of the leaves and record the data in a table. Take a digital photo of the leaves from each site.
Calculate the mean and standard deviation of leaf sizes at each site. (If you don’t know how to calculate these, please consult an online

resource.) Record these in a table like this:

Site

Mean*

Standard deviation

A

B

C

* Be sure to include units of measurement. For example, if you measure leaf length, the units will probably be cm.

For each site, determine the distance from the road by using map data. (There are a number of free online map distance tools.)
Make a graph of your results, using a spreadsheet like Excel. The graph might look something like this:
chart

Report

Your report should consist of the following components:

A brief introductory statement
Your experimental method, which is a general description of everything you did, in enough detail that someone else could reproduce the

experiment
Your table of sites, means, and standard deviations
Digital photos showing the sites and leaf samples
A short description of each site
A discussion. What can you conclude, if anything, about air pollution and damage to vegetation? How reliable are your results? Are there

any other variables that could explain the results (e.g., different exposure to sunlight at the different sites)? Did you control for other

variables?