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Primary Pollutants <br />Air quality impacts generally occur on two scales of motion, Near an individual source of <br />emissions or a collection of sources such as a crowded intersection or parking lot, levels of those <br />pollutants that are emitted in their already unhealthful form will be highest, Carbon monoxide <br />(CO) is an example of such a pollutant. Primary pollutant impacts can generally be evaluated <br />directly in comparison to appropriate clean air standards. Violations of these standards where <br />they are currently met, or a measurable worsening of an existing or future violation, would be <br />considered a significant impact. Many particulates, especially fugitive dust emissions, are also <br />primary pollutants. Because of the non - attainment status of the South Coast Air Basin (SCAB) <br />for PM -10, an aggressive dust control program is required to control fugitive dust during project <br />construction, <br />Secondary Pollutants <br />Many pollutants, however, require time to transform from a more benign form to a more <br />unhealthful contaminant. Their impact occurs regionally far from the source. Their incremental <br />regional impact is minute on an individual basis and cannot be quantified except through <br />complex photochemical computer models. Analysis of significance of such emissions is based <br />upon a specified amount of emissions (pounds, tons, etc.) even though there is no way to <br />translate those emissions directly into a corresponding ambient air quality impact. <br />Because of the chemical complexity of primary versus secondary pollutants, the SCAQMD has <br />designated significant emissions levels as surrogates for evaluating regional air quality impact <br />significance independent of chemical transformation processes. <br />Projects with daily emissions that exceed any of the following emission thresholds are <br />recommended by the SCAQMD to be considered significant tinder CEQA guidelines. <br />Daily Emissions Thresholds <br />Pollutant <br />Construction <br />Operations <br />ROG <br />75 <br />55 <br />NOx <br />100 <br />55 <br />CO <br />550 <br />550 <br />PM -10 <br />150 <br />150 <br />PM -2,5 <br />55 <br />55 <br />sox <br />150 <br />150 <br />Lead <br />3 <br />3 <br />Source: SCAQtYID CEQA Air Qunlity Handbook, November, 1993 Rev. <br />MI E I "Si, AQ .3 <br />75A -124 <br />