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Ozone is formed when hydrocarbons (also known as volatile organic compounds, or VOC) and nitrogen oxides (NOx) chemically react in the presence of sunlight and heat. Hydrocarbons are emitted from automobiles, gasoline stations, paint, degreasors, cleaning fluids, and many other sources. Plants also give off some reactive hydrocarbons, such as terpenes from pine trees. Nitrogen oxides are emitted by automobiles, power plants, and other combustion processes.
Ozone production is a year-round phenomenon. However, the highest ozone levels occur during the summer when strong sunlight, high temperatures, and stagnant meteorological conditions combine to drive the chemical reactions and trap the air in the region for several days. Ozone produced under these conditions can then be transported many miles outside the urban formation area.
Ground-level ozone should not be confused with the stratospheric ozone layer that is located approximately 15 miles above the earths surface. It is this layer that shields the earth from cancer-causing ultraviolet radiation. Ozone at ground level, where it can be inhaled, is a pollutant, and is known to have harmful effects in both humans and plants. Those most susceptible to harm from ozone are the sick and elderly, newborn and unborn infants, and those with asthma and other chronic lung diseases. Ground level ozone is usually controlled by regulating sources of VOC and NO2. Control strategies include the vehicle inspection and maintenance program and implementation of rules for reasonable, achievable control technologies for industrial sources. Ozone formation can be reduced by voluntary measures such as postponing use of gasoline-powered engines until evening.
Ozone Standard Status
Utah has been in attainment to the federal ozone standard since the early 1990’s. In 1997 EPA changed the national ozone standard from a 1-hour standard (0.120 ppm) to an 8-hour standard (0.08 ppm). Since that change Utah has continued to attain the 8-hour standard. On March 12, 2008, the EPA tightened the 8-hour standard to 0.075 ppm. This action has placed several Utah counties located along the Wasatch Front in jeopardy of being designated nonattainment.
Utah must now use certified monitored ozone data from 2005 – 2007 to determine specifically which areas need to be designated nonattainment of the 0.075 ppm standard. The state must submit a recommendation to the EPA by March 2009. The EPA will then either accept or modify the state’s recommendation, based on certified data from 2006-2008, and issue a final designation by March 2010.
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Ozone maximum values tend to occur on hot cloudless summer days with low to moderate winds. In order to establish ozone trends, we compare the median of the network annual maximum values to the frequency of hot summer days (days when maximum temperature at the Salt Lake City International Airport are equal or greater than 95° Fahrenheit during June, July and August). Ozone pollution levels generally decreased in the 1980's and early 1990's, but ozone levels have slowly increased from 1992-2005. Temperature, although variable from year-to-year, is a contributor to the occurrence of high ozone values. For example, 2004 was relatively cool with no 100° Fahrenheit days recorded at the Salt Lake City International Airport.
EPA announced new ozone National Ambient Air Quality Standard.