Construction Emissions Inventory - A construction emissions inventory is designed to quantify the amounts (i.e., mass) of criteria pollutant emissions (and their precursors) associated with the construction of the proposed project /action. Based upon forecasted construction equipment and resource needs, activity levels and appropriate emission factors, the results provide an estimate o f the potential air quality impacts and enable useful comparisons between project alternatives and significance criteria. The results are typically expressed in units of tons/year segregated by pollutant type (e.g., CO, PM $_{2.5}$, PM$_{10}$, etc.), emission source (i.e., construction equipment) and alternative over the construction period. (See Section 6.1.2 , Airport Construction Emissions, and Appendix A6 , Construction Emission Inventory for Criteria Pollutants , for more information.) 

Hazardous Air Pollutant (HAPs) Emissions Inventory – HAPs are pollutants for which there are no NAAQS but are regulated and are of concern in connection with the protection of public health and the environment. Similar to the operational emissions inventory of criteria pollutants described previously, the HAPs emissions inventory is designed to quantify the amounts (i.e., mass) of emissions associated with the operation (or implementation) of the proposed project. Again, the results are typically expressed in units of tons/year , segregated by pollutant type (e.g., benzene, formaldehyde, etc.), emission source, and alternative for the study period. (See Section 6.2 , Hazardous Air Pollutants, and Appendix B , Emissions Inventory for Hazardous Air Pollutants , for more information.) 

Greenhouse Gas (GHG) Emissions Inventory – GHGs are also pollutants for which there are no NAAQS but are of concern because of their role in climate change. Similar to the operational and HAPs emissions inventories described previously, the GHG emissions inventory is designed to quantify the amounts (i.e., mass) of these emissions associated with the operation (or implementation) of the proposed project. The results are typically expressed in units of metric tons/year , segregated by emission type (e.g., CO$_{2}$, CH$_{4}$, etc.), emission source , and alternative for the study period. (See Section 6.3 , Greenhouse Gases, and Appendix C , Emissions Inventory for Greenhouse Gases , for more information.) 

Atmospheric Dispersion Modeling - Dispersion modeling is used to further refine the results of the operational and construction emissions inventory by distributing the emissions across a project/action area both spatially and temporal ly based upon operational and physical character istics of the emission source(s) combined meteorological local terrain data. With background levels added to the modeling results, the outcome(s) is/are expressed in the form of concentrations ( i.e., micrograms per cubic meter [µg/m$^{3}$] or parts per million [ppm]) of pollutants (e.g., CO, NO$_{2}$, PM$_{10}$, PM$_{2.5 }$etc.) by receptor location for direct comparison to the NAAQS. (See Section 7.1 , Atmospheric Dispersion Modeling, and Appendix D , Atmospheric Dispersion Modeling for more information.) 

Roadway Dispersion Modeling (i.e., “Hot-Spot” Analysis) – Similar to airport dispersion modeling but on a smaller scale and specific to roadway intersection analysis, hot-spot modeling is designed to assess the effects of motor vehicle traffic emissions on local air quality conditions. Again, with background values added to the modeling results, the outcome(s) is expressed in the form of concentrations ( i.e., µg/m 3 or ppm) of pollutants (i.e., CO, PM$_{2.5}$) for direct comparison to the NAAQS. (See Section 7.2 , 

