Appendix 4.5    Derivation of Emission Factors for ISCST3 Model



The odour concentration at nearby air sensitive receivers due to the operation of the proposed Wholesale Fish Market (WFM) is predicted using the dispersion model, ISCST3. The emission factors adopted in the dispersion model are derived from the odour emission rate determined for this assessment (see Appendix 4.3). It was conservatively assumed that all the odour generated inside the WFM will be discharged to the outside environment through the ventilation exhaust. To model the potential odour emission from the WFM, the point of emission is taken to be the extracted air discharge of the mechanical ventilation system. The emission factor and the dimensions of the emission sources adopted in the dispersion model are given below.


The mechanically extracted air from the WFM will be emitted to the atmosphere via a continuous rectangular discharge louvre with facial dimension of 80m´0.5m. It will be installed at 3.3m above ground level facing the seaside. In view of the linear shape of the discharge louvre, the odour emission from which was modelled as simulated line source. The line source was represented by 10 primary volume sources placed at equal intervals along the source line. To model the initial horizontal exit of the extracted air, each primary volume source is further represented by six volume sources comprising of 2/3 and 1/3 of the emission loading of the primary volume source respectively (with the three sources closer to the discharge point bearing the larger loading). The length of side of the volume source is the same as the vertical dimension of the discharge louvre, i.e. 0.5m. Location of the volume sources simulated line source used in the dispersion model is illustrated in Figure A4.4-1. The initial lateral and vertical dimensions for these volume sources adopted in the modelling were estimated as follows :


Initial lateral dimension = volume sources center to center distance divided by 2.15

                                       = 8.83/2.15 = 4.11m

Initial vertical dimension = building height divided by 2.15

                                         = 5/2.15 = 2.33m                                     


The rate of odour emission from the WFM is determined to be 1134OU/s. The emission loading is distributed among the 60 volume sources which were used to represent the line source of odour emission from the long and narrow discharge louvre. Table 1 presents the emission factors adopted for these volume sources.


Table 1    Emission Factors for ISCST3 Model

Volume Source ID (as in Figure A4.4-1)

Emission Factors

V-1, V-2, V-3, V-4,V-5, V-6, V-7, V-8, V-9,V-10


V-11, V-12, V-13, V-14,V-15, V-16, V-17, V-18, V-19,V-20


V-21, V-22, V-23, V-24,V-25, V-26, V-27, V-28, V-29,V-30


V-31, V-32, V-33, V-34,V-35, V-36, V-37, V-38, V-39,V-40


V-41, V-42, V-43, V-44,V-45, V-46, V-47, V-48, V-49,V-50


V-51, V-52, V-53, V-54,V-55, V-56, V-57, V-58, V-59,V-60