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*:/ : 11-1 h WA <br />NOz absorbs blue light; the result is a brownish -red cast to the atmosphere and reduced visibility. NO is a <br />colorless, odorless gas formed from atmospheric nitrogen and oxygen when combustion takes place under <br />high temperature and/or high pressure (SCAQMD 2005; USEPA 2018a). The SoCAB is designated as an <br />attainment area for NOz under the National AAQS California AAQS (CARB 2017a). <br />Sulfur Dioxide (SO2) is a colorless, pungent, irritating gas formed by the combustion of sulfurous fossil <br />fuels. It enters the atmosphere as a result of burning high -sulfur -content fuel oils and coal and from chemical <br />processes at chemical plants and refineries. Gasoline and natural gas have very low sulfur content and do not <br />release significant quantities of SOz (SCAQMD 2005; USEPA 2018a). When sulfur dioxide forms sulfates <br />(SO4) in the atmosphere, together these pollutants are referred to as sulfur oxides (SOx). Thus, SOz is both a <br />primary and secondary criteria air pollutant. At sufficiently high concentrations, SOz may irritate the upper <br />respiratory tract. At lower concentrations and when combined with particulates, SOz may do greater harm by <br />injuring lung tissue. The SoCAB is designated as attainment under the California and National AAQS (CARB <br />2017a). <br />Suspended Particulate Matter (PMio and PM2.5) consists of finely divided solids or liquids such as soot, <br />dust, aerosols, fumes, and mists. Two forms of fine particulates are now recognized and regulated. Inhalable <br />coarse particles, or PMto, include the particulate matter with an aerodynamic diameter of 10 microns (i.e., 10 <br />Millionths of a meter or 0.0004 inch) or less. Inhalable fine particles, or PMzs, have an aerodynamic diameter <br />of 2.5 microns (i.e., 2.5 millionths of a meter or 0.0001 inch) or less. Particulate discharge into the <br />atmosphere results primarily from industrial, agricultural, construction, and transportation activities. <br />However, wind action on and landscapes also contributes substantially to local particulate loading (i.e., <br />fugitive dust). Both PMto and PM25 may adversely affect the human respiratory system, especially in people <br />who are naturally sensitive or susceptible to breathing problems (SCAQMD 2005). <br />The US Environmental Protection Agency's (EPA) scientific review concluded that PM25, which penetrates <br />deeply into the lungs, is more likely than PMto to contribute to health effects and at concentrations that <br />extend well below those allowed by the current PMto standards. These health effects include premature death <br />and increased hospital admissions and emergency room visits (primarily the elderly and individuals with <br />cardiopulmonary disease); increased respiratory symptoms and disease (children and individuals with <br />cardiopulmonary disease such as asthma); decreased lung functions (particularly in children and individuals <br />with asthma); and alterations in lung tissue and structure and in respiratory tract defense mechanisms <br />(SCAQMD 2005). There has been emerging evidence that even smaller particulates with an aerodynamic <br />diameter of <0.1 microns of less (i.e., <0.1 millionths of a meter or <0.000004 inch), known as ultrafine <br />particulates (UFPs), have human health implications, because UFPs toxic components may initiate or facilitate <br />biological processes that may lead to adverse effects to the heart, lungs, and other organs (SCAQMD 2016). <br />However, the EPA or CARB have yet to adopt AAQS to regulate these particulates. Diesel particulate matter <br />(DPM) is classified by the CARB as a carcinogen (CARB 1998). Particulate matter can also cause <br />environmental effects such as visibility impairment,' environmental damage,z and aesthetic damage3 <br />r PMz 5 is the main cause of reduced visibility (haze) in pacts of the United States. <br />2 Particulate matter can be carried over long distances by wind and then settle on ground or water, making lakes and streams acidic; <br />changing the nutrient balance in coastal waters and large river basins; depleting the nutrients in soil; damaging sensitive forests and <br />farm crops; and affecting the diversity of ecosystems. <br />75C-143 <br />