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Introduction
When I started a new school in eighth grade, I thought the 40-minute commute each way would be a headache I would have to endure. I never imagined that it would in fact spark my curiosity, leading me on a two-year search to discover how air pollution was affecting the environment in my town, which is on Cape Cod. My head propped against the window, I would stare at the trees as they rushed by until they formed a green, brown, and rust blur on the side of the highway. Why wasn't this vista a pure green panorama, though? I leaned over and asked my dad why the trees looked so mottled and burned on the side of the road. He explained patiently that all of the salt from the roads and the air pollutants released from the cars were burning their needles and leaves. Interesting, I thought. And so I set off on a search through the research—by scientists on the East Coast who are studying jack and ponderosa pines; in the annals of Forest Watch, a group in New Hampshire that monitors air pollution damage to pine trees; and in the published work of people from all over the world, all asking the question, how is air pollution affecting our environment? As I discovered, ozone pollution at the tropospheric level is increasing rapidly, caused by increased smokestack and tailpipe emissions from combusting gas and burning coal, as well as many other sources. The ozone produced is very harmful to living things, leading to various diseases and ailments in humans, and death or damage in plants. In 1990 the EPA set new guidelines to limit the production of ground-level ozone. However, many areas greatly exceed these regulations. I realized that is necessary to start exploring the detrimental effects this ozone pollution is having on the surrounding environment so that people can see the necessity of tighter ozone-emission standards.  An Eastern White Pine (Pinus strobes) Background To understand how ozone pollution is different from the ozone layer we also hear about, I started off by researching the basics about how ozone is formed, what it does, and how it affects us and our planet. The sun both creates and destroys ozone, with photochemical reactions involving shortwave sunshine in the stratosphere (Scorer, 2002). Ozone (O3) is formed naturally when UV radiation (less that 243 nanometers long) breaks the bond between two oxygen atoms (O) that are bonded together in an oxygen molecule (O2). One of these oxygen atoms then bonds with M, a molecule of another element, usually nitrogen. The remaining oxygen atom then bonds with an oxygen molecule, producing an ozone molecule. The stratosphere, the layer of our atmosphere12 to 50 kilometers above the Earth's surface, contains 90 percent of all of the atmospheric ozone (Krupa, 1997; Reid, 2000). Without the ozone layer, it is very unlikely that life on Earth ever would have developed, because the ozone in our atmosphere absorbs the ultraviolet radiation from the sun (Krupa, Sagar V. 1997). This biologically harmful radiation, specifically the UV-B rays (280–320 nanometers in length), damages living cells and causes ailments such as skin cancer, cataracts, and wrinkles. The ozone layer keeps a large amount of this radiation from reaching the Earth's surface, where it would harm life (Krupa, 1997; Reid, 2000). However, when large amounts of ozone are present in the troposphere (the layer of our atmosphere from the surface of the Earth to about 12 kilometers in altitude), it can be harmful and is labeled "bad ozone" (Reid, 2000). Scientists initially thought that the amount of ozone in the troposphere existed in a state of dynamic equilibrium, that ozone formation and destruction happened at equal rates, and that the ozone level in the troposphere remained constant. They could not figure out an explanation when it was found that tropospheric ozone levels were rising. It wasn't until the 1950s that chemists discovered that the major contributors to ozone formation in the troposphere were volatile organic compounds (VOCs) and nitrogen oxides. These originate chiefly from the burning of gasoline and other fossil fuels (USDA-ARS, 1998). Volatile organic compounds, such as hydrocarbons, derive from the evaporation of liquid fuels, solvents, and organic chemicals. VOCs also come from gasoline combustion and are emitted naturally by some plants and bacterial processes in soil (Chemistry in the Sunlight). Between 1900 and 1970, as the use of automobiles skyrocketed, the production of VOCs increased 690 percent (Delnore, April 3, 2002). Nitrogen oxides can be created naturally by lightning, forest fires, burning biomass, and chemical processes in soils. However, nitrogen oxides also derive from the combustion of fossil fuels at high temperatures: from the smokestack and tailpipe emissions of automobiles, diesel trucks and buses, farming and construction equipment, boats and trains. The primary source of nitrogen oxides in the United States is coal-fired power plants (Chemistry in the Sunlight). |
Ozone is the most widespread pollutant in Europe and North America, and at the tropospheric level it is very damaging to the tissues of living things (Finnish Environment Institute, 1998). In humans, exposure to ozone can aggravate or increase susceptibility to respiratory conditions and illnesses such as asthma, bronchitis, and pneumonia. It also reduces lung function and the capacity for exercise, and can trigger symptoms such as wheezing, coughing, and pain while taking deep breaths. It does this by irritating the lung airways and causing inflammation, much like a sunburn. It can also cause chest pains and coughing. Ozone particularly affects young children and the elderly, but high ozone levels can affect healthy people who are active outdoors. Permanent lung damage can occur if a person spends several months with repeated exposure to ozone pollution, even though the levels are not that high (Delnore, 2002).
The corrosive nature of ozone can damage plant tissue and destroy forest and agricultural vegetation (Delnore, 2002). Ozone causes more damage to vegetation than all other air pollutants combined (USDA-ARS, 1998). It hinders the ability of plants to produce and store food, which in turn makes them more susceptible to insects, other pollutants, disease, and harsh weather. Ozone reduces crop yield and damages the leaves and needles of trees, ruining the gorgeous appearance of forests and national parks (U.S. Department of Environmental Protection, Office of Air Quality, Planning & Standards, 2000). When a plant is exposed to ozone, its visible symptoms are classified as either acute or chronic. Acute responses happen within a few hours or days and are usually a result of exposure to high levels of ozone pollution. The symptoms include the death of cells, resulting in stippling, flecking, bleaching, and bifacial necrosis. Chronic injury is a characteristic response to long-term low-concentration exposure. The symptoms develop more slowly, and may include chlorosis, pigmentation, and necrosis. In conifers, damage due to ozone pollution is most commonly expressed by chlorotic mottle and tip necrosis (or tip burn), along with needle shortening (Finnish Environment Institute, 1998). I focused on ozone pollution's damage to the Eastern White Pine, or Pinus strobes. This tree is the largest of the northeastern conifers and grows up to 100 feet high, though it used to reach heights of 150 feet or more. The pines have rows of horizontal branches, forming a broad and irregular crown around each trunk, which can reach two to four feet in diameter. The evergreen needles of the white pine come in blue-green bundles of five and are whorled, slender, and 2.5 to 5 inches long; the cones are 4 to 8 inches long, yellow-brown, and narrowly cylindrical (Mirov, 1967; Sutton, 1992). In white pines, whorl retention and fascicle retention cannot be measured, because white pines do not grow in a whorl formation, or have a specific number of fascicles in bundles. The percent of living crown is also not relevant on a white pine. The symptoms that indicate ozone damage for a white pine are the average needle length, tip necrosis, and chlorotic mottle.  Figures 1 and 2 (Click to view) When the stomatas open, generally in the early morning (Air Quality and Ozone Injury to Forests), ozone enters through them and damages the sensitive mesophyll tissue surrounding the stomatal opening (Forest Watch). The mesophyll tissue is vital in photosynthesis; the ozone reduces the net photosynthesis of pines by degrading the chlorophyll within the cells. It also reduces growth and makes trees more vulnerable to natural pests such as the pine bark beetle (Development and Application of the Ozone Injury Index, 1996). Another characteristic of ozone-damaged white pines is tip necrosis, or death of the end of the needles. White pine needles tend to have brown tips as they age, but ozone damage accentuates this. When tip necrosis is combined with symptoms such as chlorotic mottle, the occurrence of ozone damage is almost certain (Forest Watch). It is important to understand that one can be exposed to high levels of ozone even if one doesn't live in a highly industrialized area. Industrial and urban areas release ozone-forming pollutants that are blown long distances by the wind, and then heat and sunlight cause them to form ozone. The concentration of ozone can actually increase the further it gets from urban centers. Hours and sometimes days after pollutants are released into the air, they form ozone in downwind areas (U.S. Dept. of Environmental Protection, Office of Air Quality, Planning & Standards, 2000). Therefore, it is necessary to measure local levels of ozone to get an accurate representation of the ozone pollution for a certain area. Millions of Americans live in places with ozone concentrations that exceed the EPA's air-quality standards. Areas with extremely high levels of ozone pollution are the Northeast, the Lake Michigan area, parts of the Southeast, southeastern Texas, and parts of California (U.S. Dept. of Environmental Protection, Office of Air Quality, Planning & Standards, 2000). |
 
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