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Ozone <br />Ozone (O3) is a colorless gas with a pungent odor. Most ozone in the atmosphere is formed as a <br />result of the interaction of ultraviolet light, reactive organic gases (ROG), and oxides of nitrogen <br />(NOX). ROG (the organic compound fraction relevant to ozone formation, and sufficiently equivalent <br />for the purposes of this analysis to volatile organic compounds, or VOC), is composed of non- <br />methane hydrocarbons (with some specific exclusions), and NOX is made of different chemical <br />combinations of nitrogen and oxygen, mainly nitric oxide (NO) and nitrogen dioxide (NO2). As highly <br />reactive molecule, ozone readily combines with many different components of the atmosphere. <br />Consequently, high levels of O3 tend to exist only while high ROG and NOX levels are present to <br />sustain the O3 formation process. Once the precursors have been depleted, O3 levels rapidly decline. <br />Because these reactions occur on a regional rather than local scale, O3 is considered a regional <br />pollutant. <br />Carbon Monoxide <br />CO is an odorless, colorless gas and causes a number of health problems including fatigue, <br />headache, confusion, and dizziness. The incomplete combustion of petroleum fuels in on-road <br />vehicles and at power plants is a major cause of CO. CO is also produced during the winter from <br />wood stoves and fireplaces. CO tends to dissipate rapidly into the atmosphere; consequently, <br />violations of the State CO standard are generally associated with major roadway intersections <br />during peak-hour traffic conditions. <br />Localized CO “hotspots” can occur at intersections with heavy peak-hour traffic. Specifically, <br />hotspots can be created at intersections where traffic levels are sufficiently high such that the local <br />CO concentration exceeds the National Ambient Air Quality Standards (NAAQS) of 35.0 parts per <br />million (ppm) or the State AAQS of 20.0 ppm. <br />Nitrogen Dioxide <br />NO2 is a by-product of fuel combustion, with the primary source being motor vehicles and industrial <br />boilers and furnaces. The principal form of nitrogen oxide produced by combustion is NO, but NO <br />reacts rapidly to form NO2, creating the mixture of NO and NO2 commonly called NOX. NO2 is an <br />acute irritant. A relationship between NO2 and chronic pulmonary fibrosis may exist, and an increase <br />in bronchitis in young children at concentrations below 0.3 parts per million (ppm) may occur. NO2 <br />absorbs blue light and causes a reddish brown cast to the atmosphere and reduced visibility. It can <br />also contribute to the formation of particulate matter no more than 10 microns in diameter (PM10) <br />and acid rain. <br />Suspended Particulates <br />PM10 is small particulate matter measuring no more than 10 microns in diameter, while PM2.5 is fine <br />particulate matter measuring no more than 2.5 microns in diameter. Suspended particulates are <br />mostly dust particles, nitrates, and sulfates. They are a by-product of fuel combustion and wind <br />erosion of soil and unpaved roads, and are directly emitted into the atmosphere through these <br />processes. Suspended particulates are also created in the atmosphere through chemical reactions. <br />The characteristics, sources, and potential health effects associated with the small particulates <br />(those between 2.5 and 10 microns in diameter) and fine particulates (PM2.5) can be very different. <br />The small particulates generally come from windblown dust and dust kicked up from mobile <br />sources. The fine particulates are generally associated with combustion processes as well as being <br />formed in the atmosphere as a secondary pollutant through chemical reactions. Fine particulate <br />141