BENZENE EMISSION FACTOR FOR DIFFERENT SOURCES:

·        Emissions from Refuelling losses

            Refuelling losses – These depend on the ambient temperature at the time of refuelling, and are determined by the following equation

                        Bz_e = 0.23 BZ_d + 0.21 BZ_f

            Where,

            Bz_e            Is the mass fraction of benzene in total hydrocarbons emitted

            BZ_d            Is the fraction of benzene in the petrol distributed

            BZ_f             Is the fraction of benzene in  the petrol in the tank

·        Emissions from Evaporative losses from the carburettor and the fuel tank :

          These results from the dissipation of heat when the engine is turned off and from variations in temperature between day and night.  The following equations have been established.

Engine stopped :  % weight of benzene in vapour = 0.45 of the weight of benzene in petrol

Respiration : % weight of benzene in vapour = 0.89 of the weight of benzene in petrol

• Emissions from  exhaust :

            BZ_exh = 0.50 +0.44 BZ_gas + 0.04 Ar

            Where

            BZ_exh                 Is the percent weight of benzene in the exhaust

            BZ_gas                 Is the percent weight of benzene in petrol (gasoline)

            Ar                    Is the percent weight of other aromatics in petrol (gasoline)

For Benzene exhaust from petrol vehicles, separate equations were used for three-way catalysts, three way plus oxidation catalysts, and other catalyst types.  For vehicles with a three- way catalyst, running on baseline gasoline, the following equation was used :

            3-way Bz%THC            = 1.077+0.7732* (Volume % benzene)

                                                  + 0.0987* (Volume % aromatics – volume % benzene)

This equation was obtained by the EPA Regulatory Development and Support Division (RDSD) from work done by Chevron Oil Company. 

For vehicles with a three-way plus oxidation catalyst, running on baseline petrol the equation used was :

            3-way + oxBz%THC            = 0.6796* (Volume % benzene)

                                                   +0.0681* (Volume % aromatics – volume % benzene)

This equation was obtained from the draft Regulatory Impact Analysis for RVP regulations (EPA, 1098 a).

  For vehicles with no catalyst or an oxidation catalyst, the equation used was :

            Other Bz%THC            = 0.8551* (Volume % benzene)

                                                    +0.12198 * (Volume % aromatics) –1.1626

·                    Benzene Emission from Gasoline Loading Racks at Bulk Terminals and Bulk Plants :

Table 5 :      Benzene Emission Factors for Gasoline Loading Racks at Bulk Terminals and Bulk Plants

Source :  EPA’s Emission Factors (1993)

a.            Gasoline factors represent emissions of non-methane VOC.  Factors are expressed as mg gasoline per liter transferred.

b.       Based on an average benzene/VOC ratio of 0.009.

c.          Submerged loading is either top or bottom submerged.

d.      Splash and submerged loading.  Calculated using a Stage 1 control efficiency

          of 95 percent.

·                    Gasoline Vapour and Benzene Emission from a Typical Service

       Station :

Table 6 :  Gasoline Vapour and Benzene Emission Factors  for a Typical Service Station

   Source :  EPA’s Emission Factors (1993)

a)       Typical service station considering a gasoline throughout of 19,000 liters/day (5,000).

b)       Based on gasoline emission factor and an average benzene/VOC ratio of 0.009

c)            Calculated using a Stage 1 control efficiency of 95 percent.

d)       Vehicle refuelling emission factors can also be derived for specific geographic locations and for different seasons of the year using the MOBILE 5a.  EPA’s mobile source emission factor computer model.

·              Gasoline Vapour and Benzene Emission from a Typical Bulk Plant :

Table 7 :  Gasoline Vapour and Benzene Emission Factors for a Typical 

                  Bulk Plant

 Source :  EPA’s Emission Factors (1993)

(A)       Typical bulk plant with gasoline throughout of 19,000 liters/day (5,000 gallons/day)

(B)       Based on gasoline emission factors and an average benzene /VOC ratio of

            0.009

(C)            Calculated using a Stage 1 control efficiency of 95 percent.

·        Benzene Emissions from Locomotives and Aircraft Loading and Take Off  :

Table 8 : Benzene Emissions Factors for Locomotives and Benzene 

               Content  In Aircraft Loading and Take Off Emission’s

Source :  EPA’s Emission Factors (1993)

a. These fractions are found in Appendix B6 of EPA, 1993, and represent toxic emission fractions for heavy-duty diesel vehicles.  Toxic fractions for locomotive are assumed to be the same, since no fractions specific for locomotive are available.  It should be noted that these fractions are based on g/mile emissions data, whereas emission factors for locomotives are estimated in Ib/gal.  The toxic emission fractions were multiplied by the HC emission factors to obtain the toxic emission factors.

Toluene and Xylene are used as solvent in rubber and plastic cement and in manufacturing of some compounds.  During the production process.  Toluene and Xylene vaporised and find their way into the air.