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*:/:I1-3Ill ira <br />To assist lead agencies, SCAQMD developed screening level ISTs to backcalculatethe mass amount (lbs. per <br />day) of emissions generated onsite that would trigger the levels shown in Table 5 for projects under 5-acres. <br />These "screening level" LSTs tables are the localized significance thresholds for all projects of five acres and <br />less; however, it can be used as screening criteria for larger projects to determine whether or not dispersion <br />modeling may be required to compare concentrations of air pollutants generated by the project to the <br />localized concentrations shown in Table 5. <br />In accordance with SCAQMD's IST methodology, the screening level construction LSTs are based on the <br />acreage disturbed per day based on equipment use. The screening level construction LSTs for the project site <br />in SRA 17 are shown in Table 6, SCAQMD Screening Lewl Conrtruckan L ocak ed Significance Thresholds. <br />Table 6 SCAQMD Screening -Level Construction Localized Significance <br />Thresholds <br />Threshold (lbslday) <br />Carbon Coarse Fine <br />Nitrogen Monoxide Particulates Particulates <br />Acreage Disturbed Oxides NOz CO PMra PM2.5 <br />1.09 Acres Disturbed Per Day 84 1 506 1 4 1 3 <br />1.00 Acres Disturbed Per Day 81 1 485 1 4 1 3 <br />Soume. SCAQMD 20081b, SCAQMD 2011, Based on receptors in SRA 17. LSTs are based on receptors within 82 feet <br />(25 meters). <br />GREENHOUSE GAS EMISSIONS <br />Scientists have concluded that human activities are contributing to global climate change by adding large <br />amounts of beattrappinggases, known as GHG, to the atmosphere. Climate change is the variation of <br />Earth's climate over time, whether due to natural variability or as a result of human activities. The primary <br />source of these GHG is fossil fuel use. The Intergovernmental Panel on Climate Change (IPCC) has <br />identified four major GHG water vapor,9 carbon (CO2), methane (CH4), and ozone (03)—that are the likely <br />cause of an increase in global average temperatures observed within the 20th and 21st centuries. Other GHG <br />identified by the IPCC that contribute to global warming to a lesser extent include nitrous oxide (N20), sulfur <br />hexaflumide (SF6), hydioflumocarbons, perflumocarbons, and chlorofluorocarbons (IPCC 2001).10 The <br />major GHG are briefly described below. <br />■ Carbon dioxide (CO2) enters the atmosphere through the burning of fossil fuels (oil, natural gas, and <br />coal), solid waste, trees and wood products, and respiration, and also as a result of other chemical <br />9 Water vapor (H20) is the strongest GHG and the most variable in its Abases (vapor, cloud droplets, ice crystals). However, water vapor is not <br />considered a pollutant, but part of the feedback loop o rather than a primary cause of change. <br />10 Black carbon contributes to climate change both directly, by absorbing sunlight, and indirectly, by depositing on snow (making it <br />melt faster) and by interacting with clouds and affecting cloud formation Black carbon is the most strongly light -absorbing <br />component of particulate matter (PM) emitted from burning fuels such as coal, diesel, and biomass. Reducing black carbon emissions <br />globally can have immediate economic, climate, and public health benefits. California has been an international leader in reducing <br />emissions of black carbon, with close to 95 percent control expected by 2020 due to existing programs that target reducing PM from <br />diesel engines and burning activities (CARB 2017b). However, state and national GHG inventories do not yet include black carbon <br />due to ongoing work resolving the precise global warming potential of black carbon. Guidance for CEQA documents does not yet <br />include black carbon. <br />75C-154 <br />