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.