ARCHIVED REPORTS_DRAFT ENVIRONMENTAL IMPACT REPORT

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reactions between reactive organic gases (ROG)and NOx. These photochemical reactions, in turn,result in ozone formation. During the summer,wind speed and direction data indicate that summer wind usually originates at the north end of the San Joaquin Valley and flows in a south-southeasterly direction through Tehachapi Pass and into the Southeast Desert Air Basin(SJVAPCD 2002). EXISTING AIR QUALITY CONDITIONS—CRITERIA AIR POLLUTANTS Concentrations of the following air pollutants: ozone, CO,nitrogen dioxide(NOA sulfur dioxide(SO2), respirable and fine particulate matter(PM10 and PM2.5), and lead are used as indicators of ambient air quality conditions. Because these are the most prevalent air pollutants known to be deleterious to human health, and because there is extensive documentation available on health-effects criteria for these pollutants,they are commonly referred to as"criteria air pollutants." A brief description of each criteria air pollutant, including source types,health effects, and future trends, is provided below along with the most current attainment area designations and monitoring data for the project area and vicinity. Ozone Ozone is a photochemical oxidant, a substance whose oxygen combines chemically with another substance in the presence of sunlight, and the primary component of smog. Ozone is not directly emitted into the air,but is formed through complex chemical reactions between precursor emissions of ROG and NOx in the presence of sunlight. ROG are volatile organic compounds that are photochemically reactive. ROG emissions result primarily from incomplete combustion and the evaporation of chemical solvents and fuels.NOx are a group of gaseous compounds of nitrogen and oxygen that results from the combustion of fuels. A highly reactive molecule, ozone readily combines with many different components of the atmosphere. Consequently,high levels of ozone tend to exist only while high ROG and NOx levels are present to sustain the ozone formation process. Once the precursors have been depleted, ozone levels rapidly decline. Because these reactions occur on a regional scale, ozone is considered a regional pollutant. Ozone located in the upper atmosphere(stratosphere) acts in a beneficial manner by shielding the earth from harmful ultraviolet radiation that is emitted by the sun. However, ozone located in the lower atmosphere (troposphere)is a major health and environmental concern. Meteorology and terrain play a major role in ozone formation. Generally, low wind speeds or stagnant air coupled with warm temperatures and clear skies provide the optimum conditions for formation. As a result, summer is generally the peak ozone season. Because of the reaction time involved,peak ozone concentrations often occur far downwind of the precursor emissions. Therefore, ozone is a regional pollutant that often affects large areas. In general, ozone concentrations over or near urban and rural areas reflect an interplay of emissions of ozone precursors,transport,meteorology, and atmospheric chemistry(Godish 1991). The adverse health effects associated with exposure to ozone pertain primarily to the respiratory system. Scientific evidence indicates that ambient levels of ozone affect not only sensitive receptors, such as asthmatics and children,but healthy adults as well. Exposure to ambient levels of ozone ranging from 0.10 to 0.40 part per million(ppm) for 1-2 hours has been found to significantly alter lung functions by increasing respiratory rates and pulmonary resistance, decreasing tidal volumes (the amount of air inhaled and exhaled), and impairing respiratory mechanics. Ambient levels of ozone above 0.12 ppm are linked to symptomatic responses that include such symptoms as throat dryness, chest tightness,headache, and nausea. In addition to the above adverse health effects, evidence also exists relating ozone exposure to an increase in permeability of respiratory epithelia; such increased permeability leads to an increased response of the respiratory system to challenges, and a decrease in the immune system's ability to defend against infection. (Godish 1991). Manteca WQCF and Collection System Master Plans EIR EDAW City of Manteca 4.3-3 Air Quality