Audience: Educating general public
How Ozone Formation Contributes to Global Warming
Chesa Ramacciotti
Introduction
Ozone, formed through the reactions of various factory emissions, is a secondary atmospheric
pollutant that negatively contributes to the process of global warming. When fossil fuels are
burned in industry and through transportation, numerous gases are emitted into the atmosphere.
Here, these gases undergo specific chemical reactions with oxygen already present in the
atmosphere. These reactions result in the creation of ozone. Once the ozone is present in the
atmosphere, it blocks the sun’s rays that are attempting to leave Earth and exit the atmosphere.
Thus, more sunlight is trapped within the lower levels of Earth’s atmosphere and leads to rising
surface temperatures. Over time, this process has led to the creation and persistence of global
warming.
The Creation of Atmospheric Pollutants
The atmosphere is made up of a combination of colorless and odorless gases, including nitrogen,
oxygen, argon, carbon dioxide, water vapor, and others. While the atmosphere is an essential
component for human survival on earth, it is frequently polluted by other gases emitted though
both natural and human activities. Air pollutants can be directly released into the environment
(primary air pollutants) or created while in the atmosphere by chemical reactions of other gases
(secondary air pollutants).
The most abundant primary air pollutants of concern include:
 Nitrogen Compounds. Nitrogen oxides include: nitrogen oxide (NO), nitrogen dioxide
(NO2), and ammonia (NH3). These gases come from sources such as vehicle emissions
and fossil fuel combustion.
 Sulfur Compounds. Sulfur containing compounds include: sulfur dioxide (SO2), sulfur
trioxide (SO3), and hydrogen sulfide (H2S). These gases are emitted mainly from
combustion of fossil fuels, particularly coal from electrical and industrial practices.
Natural processes also contribute sulfur to the atmosphere through biological reactions
and volcanic eruptions.
 Volatile Organic Compounds. Volatile organic compounds are highly toxic and are
emitted into the atmosphere through vehicle emissions and the use of volatile solvents.
Compounds included in this category consist of methane, terpenes, and trichloroethylene.
 Particulate Matter. While particulate matter is not a gaseous air pollutant, it remains a
cause for concern. These pollutants consist of both fine and coarse dust particles released
from vehicle emissions, fuel combustion, and agricultural practices.
These primary air pollutants have caused major damage to the environment themselves and have
given rise to dangerous secondary air pollutants as well.
The Formation of Ozone
Ozone (O3) is the most important secondary air pollutant of concern in the United States
currently. At high concentrations, this gas has a very pungent odor and is a powerful oxidizing
agent. While ozone can be found in multiple layers of Earth’s atmosphere, it is only an air
pollutant in the troposphere, the layer closest to Earth’s surface. Ozone that is found in the
stratosphere, higher in altitude within the atmosphere, is a necessary component of the
atmosphere that helps to protect the Earth from the sun’s harmful rays.
Ozone in the troposphere is made through chemical reactions between primary air pollutants and
oxygen. First, when exposed to intense sunlight, nitrogen dioxide (NO2) is separated into
nitrogen oxide (NO) and an individual oxygen atom. This oxygen atom then combines with
oxygen gas (O2) already present in ample amounts in the atmosphere. Thus, the free oxygen
atom combines with two other oxygen atoms to form ozone or O3.
Volatile organic compounds are also an important component in the formation of ozone. Even
after the nitrogen dioxide separates, it is inclined to reform its original gas. However, the volatile
organic compounds present in the atmosphere will react with the nitrogen oxide (NO) and make
it unavailable for reformation of nitrogen dioxide (NO2). New compounds are then formed
between nitrogen oxide and the volatile organic compounds.
Because ozone is not a primary air pollutant, its levels in the atmosphere cannot be directly
attributed to human activities. However, patterns can be seen based on its various components.
For example, ozone in the troposphere tends to increase as nitrogen dioxide emissions increase.
Thus, an area with more industrial practices or large populations with significant vehicle
emissions would tend to have higher nitrogen dioxide levels and therefore, higher ozone levels.
Furthermore, as sunlight increases, the formation of ozone increases. This holds true not only
throughout the day but also throughout the year. Ozone levels are highest form April to October
and peak when sunlight is most intense during the day. Clearly, the formation of ozone is a very
complex process that has a considerable effect on the atmosphere’s composition.
The Effect on Global Warming
As air pollutants, such as nitrogen dioxide or ozone, increase in concentration in the atmosphere,
they have a more pronounced effect on the environment. These air pollutants specifically impact
the process of global warming, or the steady increase of Earth’s global temperatures over time.
The sun’s rays are necessary for the warming of Earth; however, too much sunlight becoming
trapped within the lower layers of Earth’s atmosphere has a negative effect on the overall global
temperatures. This process is known as the greenhouse effect.
When sun’s rays travel to Earth’s surface, some pass through Earth’s atmosphere while others
are reflected back into the universe. The gases present in higher layers of the atmosphere, such as
ozone in the stratosphere mentioned earlier, help to subdue the harsh rays before they reach
Earth’s surface. Once these rays do reach Earth’s surface, most are absorbed while some are
reflected back out into the universe. However, when there is an abundance of air pollutants in the
form of greenhouse gases, especially ozone, present in the lower atmosphere, more of those
sun’s rays remain within the atmosphere as opposed to leaving Earth. With extra heat, in the
form of the sun’s rays, trapped within Earth’s atmosphere, temperatures begin to gradually rise.
As this process continues to occur over long periods of time, global warming takes effect.
Figure 1: The Greenhouse Effect
(http://commons.wikimedia.org/wiki/File:Earth's_greenhouse_effect_(US_EPA,_2012).png)
The above figure illustrates the process of how greenhouse gases affect the reflections and
absorptions of the sun’s rays. The continuation of this greenhouse effect over time leads to the
process of global warming.
Conclusion
The secondary air pollutant ozone, is first created through chemical reactions involving nitrogen
dioxide, oxygen gas, volatile organic compounds, and the addition of sunlight. Sunlight separates
nitrogen dioxide; the free oxygen atom then combines with oxygen gas to form ozone. The
volatile organic compounds then react with the nitrogen oxide to prevent it from recombining
with the free oxygen atom. Once ozone is created, it accumulates in the atmosphere and traps
sunlight close to Earth’s surface. This process occurring over long periods of time leads to a
gradual increase in global temperatures. Clearly, the formation of ozone contributes to the
process of global warming. As ozone levels increase in the atmosphere, so do Earth’s surface
temperatures around the world.