AQI Lesson Addendum
Understanding Particle Size
Sizes, both very large and very small, are often difficult for students to comprehend. Below is a graphic
from EPA that puts particulates into perspective.
Background
“Particulate matter," also known as particle pollution or PM, is a complex mixture of extremely small
particles and liquid droplets. Particle pollution is made up of a number of components, including acids
(such as nitrates and sulfates), organic chemicals, metals, and soil or dust particles.
The size of particles is directly linked to their potential for causing health problems. EPA is concerned
about particles that are 10 micrometers in diameter or smaller because those are the particles that
generally pass through the throat and nose and enter the lungs. Once inhaled, these particles can affect
the heart and lungs and cause serious health effects. EPA groups particle pollution into two categories:
"Inhalable coarse particles," such as those found near roadways and dusty industries, are larger than
2.5 micrometers and smaller than 10 micrometers in diameter.
"Fine particles," such as those found in smoke and haze, are 2.5 micrometers in diameter and smaller.
These particles can be directly emitted from sources such as forest fires, or they can form when gases
emitted from power plants, industries and automobiles react in the air.
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AQI Lesson Addendum
PM is a complex mixture of
extremely small particles and
liquid droplets know as
aerosols. PM is comprised of
acids such as nitrates and
sulfates, organic chemicals,
metals and soil and dust
particles.
Activity
Using foam pool noodles to represent hairs or cilia in the respiratory system, and paper balls, Styrofoam,
or yarn pom poms, students will be challenged to clear their lungs of various sized particles. To
represent PM 10 use 2.5” diameter balls. For PM 2.5 use small marble sized (1/2” to ¾”) balls. You will
need a large number of particles for a memorable demonstration.
This could be done with teams (more materials needed) or as a demonstration with one pool noodle for
a more controlled experience.
1. Have the “hair” student hold the pool noodle like a bat in an open area.
2. Have one or more “particle” students toss assorted pom poms close to the “hair”.
3. The job of the “hair” is to try to bat away as many balls as possible.
Synthesis
For younger students synthesis could be a discussion about what they observed. You might also provide
the image from page one, hand lenses, some grains of sand, and a hair for additional observations and
comparisons in this discussion. Possible questions might include:


If a grain of sand is so much bigger than PM10—can we see PM10 with our eyes? How about the
very tiny PM2.5?
How many of the balls (“particles”) got by the “hair”? What do you think this means if the “hair”
was protecting your lungs?
For older students, synthesis could also include graphing the data from the experiment. Students might
do a quick group design of an experiment—standardizing timing, numbers and sizes of balls, and
determining how to calculate “success” or “failure” for the hair. With several repeated trials, could a
database of information be created and graphed? This might be done as a class, or in smaller groups.
For a deeper discussion of air quality for advanced students, you might present the following challenge:
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
If the “hair” is in 2 cubic meters of air (picture 2 boxes stacked where “hair” is standing), could
we simulate Air Quality Index levels using the small balls to represent these very small particles?
Below are the AQI Index, and the NAAQS standards for Particle Pollution. Discuss and or
demonstration:
o How would you calculate representative AQI levels. Discuss your process.
o We are using ¾” balls to represent something that is really very small. Are there shortcomings to this visual model? Discuss.
o If our pom pom was represented 2 micrometer in size, how big would that
representative “1 cubic meter box” need to be for scale? Discuss your process.
AIR QUALITY INDEX FOR PARTICLE POLLUTION
Air Quality Index
Good
0-50
Health Advisory
None.
Moderate
51-100
Unusually sensitive people should consider reducing prolonged or heavy exertion.
Unhealthy for
Sensitive Groups
101-150
People with heart or lung disease, older adults, and children should reduce
prolonged or heavy exertion.
Unhealthy
151-200
People with heart or lung disease, older adults, and children should avoid prolonged
or heavy exertion. Everyone else should reduce prolonged or heavy exertion.
Very Unhealthy
201-300
People with heart or lung disease, older adults, and children should avoid all
physical activity outdoors. Everyone else should avoid prolonged or heavy exertion.
EPA has set National Ambient Air Quality Standards (NAAQS) for six principal pollutants, which are
called "criteria" pollutants. Units of measure for the standards are parts per million (ppm) by volume,
parts per billion (ppb) by volume, and micrograms per cubic meter of air (µg/m3). Below is the
standard for Particulate Matter.
PM2.5
Particle Pollution
Dec 14, 2012
PM10
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primary
Annual
12 μg/m3
annual mean, averaged over 3
years
secondary
Annual
15 μg/m3
annual mean, averaged over 3
years
primary
and
secondary
24hour
35 μg/m3
98th percentile, averaged over 3
years
primary
and
secondary
24hour
150
μg/m3
Not to be exceeded more than once
per year on average over 3 years
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