Importantly, the type(s) and number of HAPs reported in an aviation-related emissions inventory  will depend on the type of airport sources that are evaluated and, in some case, the type of fuel  and other emission characteristics of the individual source(s) involved.  For most airport emission inventories, formaldehyde occurs in the greatest amounts followed by  acetaldehyde, acrolein, and 1,3 -butadiene. These compounds are emitted in the exhaust aircraft, APUs, GSE, motor vehicle engines and, to a lesser extent, from boilers, facilities, and other stationary sources at an airport. Compounds such as benzene, ethylbenzene,  naphthalene, toluene, hexane, styrene, and xylene also occur, but in far lesser amounts.  Appendix B  ( Emissions Inventory for Hazardous Air Pollutants ) provides additional information  on computing these a viation-related emissions including the emission inventory methods, data  sources and other supporting materials.  As discussed previously, for NEPA -related HAPs emission inventories, the emphasis is “disclosing” the incremental change in emissions with proposed project alternatives) compared to the no-action alternative. For consistency, HAPs emission inventories  should also be reported in tons per year.  Table 6-5  ( HAPs Emissions Inventory Results ) provides  a sample format for reporting HAP emissions. For simplification, total values are shown for each  species of HAPs evaluated and comprise emissions from aircraft, APUs, GSE, motor vehicles,  stationary sources, and fuel storage facilities.  48$_{ }$ Table 6-5. HAPs Emissions Inventory Results  Pollutant  HAPs Emissions Inventory (tons per year)  No Action  Alternative A  Alternative B  Year 1  Year 2  Year 1  Year 2  Year 1  Year 2  1,3-butadiene  3.92  4.58  3.93  4.45  3.80  4.58  2,2,4-trimethylpentane  0.28  0.23  0.28  0.23  0.28  0.23  2-methylnaphthalene  0.43  0.51  0.44  0.50  0.42  0.51  Acetaldehyde  9.92  11.6  9.95  11.3  9.61  11.6  Acetone  0.88  1.02  0.88  0.99  0.85  1.02  Acrolein  5.27  6.18  5.29  6.01  5.08  6.18  Benzaldehyde  1.03  1.20  1.03  1.17  0.99  1.20  Benzene  7.23  8.14  7.24  8.00  7.21  8.22  Chlorobenzene  <0.01  <0.01  <0.01  <0.01  <0.01  <0.01  Cyclohexane  0.02  0.02  0.03  0.03  0.03  0.03  Ethylbenzene  0.85  0.94  0.85  0.92  0.83  0.93  Formaldehyde  27.7  32.4  27.8  31.5  26.8  32.4  Isopropylbenzene (cumene)  0.03  0.04  0.03  0.04  0.03  0.04  M & P-xylene  1.92  2.19  1.92  2.17  1.90  2.19  Methyl alcohol  3.80  4.47  3.81  4.34  3.66  4.47  M-xylene  0.34  0.29  0.34  0.29  0.34  0.3  Naphthalene  1.23  1.44  1.23  1.40  1.18  1.44  N-heptane  0.49  0.52  0.50  0.52  0.49  0.52  N-hexane  0.77  0.78  0.77  0.78  0.77  0.78  O-xylene  1.08  1.18  1.08  1.17  1.06  1.18  Aviation Emissions and Air Quality Handbook  6.2.4.  HAPs Emission Inventory Results 