Aviation Emissions and Air Quality Handbook  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 ,  24$_{ }$