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34 Table 3-2. 100-year GWPs from Non-CO2 Appropriate GWP IPCC Fourth Assessment Report. Emissions Pollutant GWP100 CO2 1 CH4 25 N 2O 298 Calculate SF6 22,800 for any of these other pollutants reported in the inventory, no CO2 Equivalent CO2 equivalent (CO2e) emissions can be developed. Even if Emissions for Non- GWPs are available for a pollutant, the original mass emis- CO2 Pollutant sions for that pollutant should still be reported in addition to the CO2e emissions. Figure 3-16. Overview of CO2 equivalency calculations. Both the mass emissions of each of the non- CO2 pollutants and its CO2e emissions should be 3.10 Calculation of CO2 reported. Equivalencies After each applicable source has been addressed and the emissions of each pollutant have been calculated, CO2 equiv- The 100-year notation in Table 3-2 refers to the corre- alencies need to be developed as indicated in Figure 3-16. sponding time horizon for the GWP values. In keeping with The GWPs from the IPCC's fourth and most recent assess- the general protocols of both IPCC and USEPA, the GWP100 ment report (IPCC 2007) should be used, and this source values should always be used. Whether the GWPs for other needs to be clearly cited. However, based on the needs of the time horizons should be used (i.e., in addition to GWP100) airport (e.g., comparisons to older inventories), GWPs from will depend on the needs of the airport and/or the purpose of other reports could potentially be used as long as the sources the inventory. are clearly stated. GWPs from the IPCC Fourth Assessment The following is an example calculation for 10 metric tons Report are reproduced in Table 3-2 for some pollutants. of CH4: CO2e emissions = (10 metric tons CH4 ) ( 25 GWP100 for CH4 ) Sources of GWP factors should be clearly identi- = 250 metric tons CO2e fied, as well as the emissions of individual pollu- tants prior to the application of the GWP. The recommended format for reporting CO2e is exempli- fied in Table 3-3. As indicated in the table, the mass emissions of each pollu- GWPs for HFC and PFC depend on the specific fluorinated tant are reported along with CO2e values. This is recom- species. Values for some other pollutants can be found in the mended as it would enable swift updates to the CO2e should IPCC report. However, most of the pollutants outside of the new and improved GWPs be developed in the future. Further six Kyoto pollutants (e.g., precursors) will not have GWPs. So, information on CO2e can be found in Appendix D. Table 3-3. Example format for reporting equivalencies (CO2e). Annual Metric Tons Metrics CO2 CH4 N 2O SF6 Others Source X Not 1,000 4 2 0.01 Emissions Assessed GWP100 1 25 298 22,800 CO2e Not 1,000 100 596 228 Assessed Total CO2e 1,924 Note: The above GWP100 factors represent emissions from IPCC's Fourth Assessment Report.