Air Pollution
Understanding and monitoring air quality is essential to atmospheric scientists to help reduce emissions,
protect human health and the environment. In this learning module, we will learn about air pollutants,
their sources, and the effects on the environment and our respiratory systems. Earth’s atmosphere
• mixture of gases that forms a layer about 250 miles thick around the earth
• bottom 5 - 11 miles (7 - 16 km) contains most (75%) of the air
Atmosphere layers
The atmosphere consists of five layers: the troposphere, the stratosphere, the mesosphere, the
thermosphere, and the exosphere. The thickness of these layers is slightly different around the globe,
and also varies according to temperature and season. In this discussion, we will focus primarily on the
troposphere and the stratosphere because they are the most affected by anthropogenic (or man-made)
pollutants.
The troposphere is the layer closest to the Earth's surface. It is a layer of air approximately 10 to 15
kilometers thick that is constantly in motion. The conditions in this layer determine practically all of the
Earth's weather patterns. It derives its name from the Greek word "Tropos," meaning "turning" or
"mixing." The constant motion in this layer is significant in discussing air quality because it results in the
dispersion of pollutants. In one respect this dispersion is considered beneficial because it has the effect
of diluting pollutants, which can reduce harmful impacts on a local level. On the other hand, this
dispersion also results in the movement of air pollutants (and therefore air pollution problems) from
areas of high pollution production to areas of lower production. For example, pollutants produced in an
industrialized and heavily populated city often adversely impact smaller communities and ecosystems in
a large surrounding area.
The stratosphere is the layer just above the troposphere. It is approximately 40 kilometers thick and is
composed mostly of dry stable air. In contrast to the troposphere, pollutants in the stratosphere do not
disperse, and tend to remain in the atmosphere for long periods of time.
Layers of the Earth's atmosphere. (adapted from G.W. Vantoon and S.J. Duffy, Environmental Chemistry:
A Global Perspective, Oxford University Press, 2000.)
As electromagnetic radiation travels through the atmosphere, shorter wavelengths are absorbed by the
molecules in the first few miles. This high frequency radiation is capable of stripping the electrons from
the molecules and dissociating the O2 and N2 molecules into O and N atoms, and ions or charged units
such as O2+, N2+ (O2 and N2 molecules with one electron missing), etc. Thus the upper layers of the
atmosphere are also called the ionosphere because they contain ions (or charged atoms and molecules).
Only radiation of wavelength 220 nm or longer penetrates deeper into the atmosphere, reaching the
stratosphere.
Composition of the Atmosphere
The first, nitrogen, is the largest constituent of the atmosphere. If the air were made of 1000 parts,
nitrogen would call for 780 parts, or 78%. Nitrogen is really important to us because it helps plants to
gain minerals from the soil for plant growth. The next most common gas that is in air is oxygen. Oxygen
, makes up 209, or 20.9% of our air. Oxygen is important for many things. We need it to breath, but it is
also needed for fires. The only problem is with oxygen, if you have too much of it, oxygen is extremely
reactive. Things could combust if you have an oxygen-rich environment, so having the nitrogen in our air
balances it out and gives us the right percentage of oxygen and nitrogen together to make air safe to
breath and be around.
The next gas in the air is called argon. Argon does not do much for us in the atmosphere, but we have 9
parts, or 0.9% in the air. Argon is a gas that can be placed in a tube with an electric current to create a
purple hue in a neon sign. Next, we have a gas that we hear a lot about these days, which is carbon
dioxide. This gas is one of the trace gases and is found in small concentrations in the atmosphere.
Carbon dioxide is a gas that we exhale when we breathe. It is also taken in by plants to create the plant’s
structure. Recall from the temperature learning module that carbon dioxide is a greenhouse gas and
allows incoming solar radiation to pass through the atmosphere, but traps outgoing or reflected sunlight
to cause a warming effect in our atmosphere. Trace gases, including carbon dioxide, make up 1 part, or
0.1% of the air. Other trace gases include ozone, nitrous oxide, methane, helium, neon, water vapor,
and several others.
• 99% of our atmosphere is made of oxygen (O2) at 21% and 78% nitrogen (N2). These gases are
transparent to both visible light from the sun and thermal infrared light from the earth.
• Greenhouse gases, like water vapor, carbon dioxide and methane, are vitally important for keeping
our planet warm.
• Although these gases are found in small concentrations, they are vitally important in maintaining a
globally averaged temperature of 59oF.
Pollutants
So, what is air pollution? It is not only chemicals in the atmosphere, but chemicals that have bad health
effects. Since we are breathing it in, it is going to affect our lungs and can lead to increased cancer risks.
So if they are affecting us negatively, we call them pollutants. The following are primary pollutants,
which means they are emitted directly into the atmosphere by a particular source. Primary pollutants
can combine with other chemicals in the atmosphere and produce secondary pollutants.
Primary Pollutants
1. Volatile organic compounds (VOCs) such as gases from evaporating gasoline.
o Volatile organic compounds (hydrocarbons) - methane, benzene, propane, &
chlorofluorocarbons (CFC's)
source = motor vehicles (evaporation from gas tanks), industry, & various
household products
18 million tons released each year in U.S.
Concentrations of many VOCs are consistently higher indoors than outdoors. A
study by the EPA, covering six communities in various parts of the United States,
found indoor levels up to ten times higher than those outdoors-even in
Understanding and monitoring air quality is essential to atmospheric scientists to help reduce emissions,
protect human health and the environment. In this learning module, we will learn about air pollutants,
their sources, and the effects on the environment and our respiratory systems. Earth’s atmosphere
• mixture of gases that forms a layer about 250 miles thick around the earth
• bottom 5 - 11 miles (7 - 16 km) contains most (75%) of the air
Atmosphere layers
The atmosphere consists of five layers: the troposphere, the stratosphere, the mesosphere, the
thermosphere, and the exosphere. The thickness of these layers is slightly different around the globe,
and also varies according to temperature and season. In this discussion, we will focus primarily on the
troposphere and the stratosphere because they are the most affected by anthropogenic (or man-made)
pollutants.
The troposphere is the layer closest to the Earth's surface. It is a layer of air approximately 10 to 15
kilometers thick that is constantly in motion. The conditions in this layer determine practically all of the
Earth's weather patterns. It derives its name from the Greek word "Tropos," meaning "turning" or
"mixing." The constant motion in this layer is significant in discussing air quality because it results in the
dispersion of pollutants. In one respect this dispersion is considered beneficial because it has the effect
of diluting pollutants, which can reduce harmful impacts on a local level. On the other hand, this
dispersion also results in the movement of air pollutants (and therefore air pollution problems) from
areas of high pollution production to areas of lower production. For example, pollutants produced in an
industrialized and heavily populated city often adversely impact smaller communities and ecosystems in
a large surrounding area.
The stratosphere is the layer just above the troposphere. It is approximately 40 kilometers thick and is
composed mostly of dry stable air. In contrast to the troposphere, pollutants in the stratosphere do not
disperse, and tend to remain in the atmosphere for long periods of time.
Layers of the Earth's atmosphere. (adapted from G.W. Vantoon and S.J. Duffy, Environmental Chemistry:
A Global Perspective, Oxford University Press, 2000.)
As electromagnetic radiation travels through the atmosphere, shorter wavelengths are absorbed by the
molecules in the first few miles. This high frequency radiation is capable of stripping the electrons from
the molecules and dissociating the O2 and N2 molecules into O and N atoms, and ions or charged units
such as O2+, N2+ (O2 and N2 molecules with one electron missing), etc. Thus the upper layers of the
atmosphere are also called the ionosphere because they contain ions (or charged atoms and molecules).
Only radiation of wavelength 220 nm or longer penetrates deeper into the atmosphere, reaching the
stratosphere.
Composition of the Atmosphere
The first, nitrogen, is the largest constituent of the atmosphere. If the air were made of 1000 parts,
nitrogen would call for 780 parts, or 78%. Nitrogen is really important to us because it helps plants to
gain minerals from the soil for plant growth. The next most common gas that is in air is oxygen. Oxygen
, makes up 209, or 20.9% of our air. Oxygen is important for many things. We need it to breath, but it is
also needed for fires. The only problem is with oxygen, if you have too much of it, oxygen is extremely
reactive. Things could combust if you have an oxygen-rich environment, so having the nitrogen in our air
balances it out and gives us the right percentage of oxygen and nitrogen together to make air safe to
breath and be around.
The next gas in the air is called argon. Argon does not do much for us in the atmosphere, but we have 9
parts, or 0.9% in the air. Argon is a gas that can be placed in a tube with an electric current to create a
purple hue in a neon sign. Next, we have a gas that we hear a lot about these days, which is carbon
dioxide. This gas is one of the trace gases and is found in small concentrations in the atmosphere.
Carbon dioxide is a gas that we exhale when we breathe. It is also taken in by plants to create the plant’s
structure. Recall from the temperature learning module that carbon dioxide is a greenhouse gas and
allows incoming solar radiation to pass through the atmosphere, but traps outgoing or reflected sunlight
to cause a warming effect in our atmosphere. Trace gases, including carbon dioxide, make up 1 part, or
0.1% of the air. Other trace gases include ozone, nitrous oxide, methane, helium, neon, water vapor,
and several others.
• 99% of our atmosphere is made of oxygen (O2) at 21% and 78% nitrogen (N2). These gases are
transparent to both visible light from the sun and thermal infrared light from the earth.
• Greenhouse gases, like water vapor, carbon dioxide and methane, are vitally important for keeping
our planet warm.
• Although these gases are found in small concentrations, they are vitally important in maintaining a
globally averaged temperature of 59oF.
Pollutants
So, what is air pollution? It is not only chemicals in the atmosphere, but chemicals that have bad health
effects. Since we are breathing it in, it is going to affect our lungs and can lead to increased cancer risks.
So if they are affecting us negatively, we call them pollutants. The following are primary pollutants,
which means they are emitted directly into the atmosphere by a particular source. Primary pollutants
can combine with other chemicals in the atmosphere and produce secondary pollutants.
Primary Pollutants
1. Volatile organic compounds (VOCs) such as gases from evaporating gasoline.
o Volatile organic compounds (hydrocarbons) - methane, benzene, propane, &
chlorofluorocarbons (CFC's)
source = motor vehicles (evaporation from gas tanks), industry, & various
household products
18 million tons released each year in U.S.
Concentrations of many VOCs are consistently higher indoors than outdoors. A
study by the EPA, covering six communities in various parts of the United States,
found indoor levels up to ten times higher than those outdoors-even in
