Air & Transportation

Control of Offensive Odor

Regulation Standards

Ordinance of the Prime Minister's Office of No. 39 of 1972,
Latest amendment by Environment Agency Notication No.6 of 2002

  1. Specified Offensive Odor Substances
  2. Odor Index

1.Specified Offensive Odor Substances(Cabinet Order No. 207 of 1972)

Ammonia NH3 Isovaleraldehyde (CH3)2CHCH2OH
Methyl mercaptan CH3SH Isobutyl alcohol (CH3)2CHCH2OH
Hydrogen sulfide H2S Ethyl acetate CH3CO2C2H5
Dimethyl sulfide (CH3)2S Methyl isobutyl ketone CH3COCH2CH(CH3)2
Dimethyl disulfide CH3SSCH3 Toluene C6H5CH3
Trimethylamine (CH3)3N Styrene C6H5CH=CH2
Acetaldehyde CH3CHO Xylene C6H4(CH3)2
Propionaldehyde CH3CH2CHO Propionic acid CH3CH2COOH
Butyraldehyde CH3(CH2)2CHO Butyric acid CH3(CH2)2COOH
Isobutyraldehyde (CH3)2CHCHO Valeric acid CH3(CH2)3COOH
Valericaldehyde CH3(CH2)3CHO Isovaleric acid (CH3)2CHCH2COOH

1.1 Range of Maximum Permissible Concentration (MPC) of Specified Offensive Odor Substances

(ppm) (ppm)
Ammonia 1MPC5 Isovaleraldehyde 0.003MPC0.01
Methyl mercaptan 0.002MPC0.01 Isobutyl alcohol 0.9MPC20
Hydrogen sulfide 0.02MPC0.2 Ethyl acetate 3MPC20
Dimethyl sulfide 0.01MPC0.2 Methyl isobutyl ketone 1MPC6
Dimethyl disulfide 0.009MPC0.1 Toluene 10MPC60
Trimethylamine 0.005MPC0.07 Styrene 0.4MPC2
Acetaldehyde 0.05MPC0.5 Xylene 1MPC5
Propionaldehyde 0.05MPC0.5 Propionic acid 0.03MPC0.2
Butyraldehyde 0.009MPC0.08 Butyric acid 0.001MPC0.006
Isobutyraldehyde 0.02MPC0.2 Valeric acid 0.0009MPC0.004
Valericaldehyde 0.009MPC0.05 Isovaleric acid 0.001MPC0.01
Concentrations of the specified offensive odor substances are measured at the ground surface on the boundary line of a place of business.

1.2 Regulation Standards of Flow Rate or Concentration of the Specified Offensive Odor Substances at the Point of Emission from Smoke Stacks Other Facilities

1.2.1 Flow rate

The regulation standard of flow rate shall be calculated using the following equation for each kind of specified offensive odor substance (excluding nine substances*)

=Flow rate of specified offensive odor substance (m 3 /hour calculated at 0ーC and at 1 atm)
=Corrected height of stack) (see 1.2.2)
=Maximum permissible concentration of substance within the range of paragraph 1.1 (ppm [ parts per million])

This equation, however, shall not be applied if the corrected height of the stack is less than 5 meters.

* Nine specified offensive odor substances are Methyl mercaptan, Dimethyl sulfide, Dimethyl disulfide, Acetaldehyde, Styrene, Propionic acid, Butyric acid, Valeric acid, and Isovaleric acid.

1.2.2 Corrected height of a stack
Adjustment of the height of a smoke stack shall be done in accordance with the following equation
=Corrected height of stack (m)
=Actual height of stack (m)
=Flow rate of exhaust gas at 15ーC (m 3 /sec)
=Exhaust velocity of exhaust gas (m/sec)
=Temperature of exhaust gas (k)

1.3 Regulation Standards of Concentration of Specified Offensive Odor Substances in the Effluent discharged from the Place of Business

The regulation standard is calculated by (only for four sulfur compounds among 22 specified offensive odor substances):

=Regulation standard of concentration of specified offensive odor substance in effluent (mg/l)
=Constant (determined depending on volume of effluent (Q) discharged from a place of business (mg/l)
=Maximum permissible concentration of substance within the range of paragraph 1.1(ppm)

Table 1. Values of Constant k (Unit of Q: m3/s)

Effluent volume (Q) Q 10-3 10-3 Q 10-1 10-1 Q
Hydrogen sulfide (H2S) 5.6 1.2 0.26
Methyl mercaptan (MM) 16 34 0.71
Dimethyl sulfide (DMS) 32 6.9 1.4
Dimethyl disulfide (DMDS) 63 14 2.9

Table 2 shows regulation standards of concentrations of four sulfur compounds in effluents corresponding to odor intensity of 2.5 ,3.0 and 3.5, as calculated by the equation above.

Table 2. Regulation standards of concentrations of four sulfur compounds in effluents (mg/l)

Effluent volume (m3/s) Q 10-3 10-3 Q 10-1 10-1 Q
Odor intensity 2.5 3.0 3.5 2.5 3.0 3.5 2.5 3.0 3.5
Hydrogen sulfide 0.1 0.3 1 0.02 0.07 0.2 0.005 0.02 0.05
Methyl mercaptan 0.03 0.06 0.2 0.007 0.01 0.03 0.001* 0.003 0.007
Dimethyl sulfide 0.3 2 6 0.07 0.3 1 0.01 0.07 0.3
Dimethyl disulfide 0.6 2 6 0.1 0.4 1 0.03 0.09 0.3
Note *:
The regulation standard should be 0.002 mg/l as a measurement limit.

2. Allowable Ranges of Odor Index

The range of the regulation standard for odor index is determined to be equivalent to 2.5-3.5 of odor intensity (levels at which the majority of local residents do not feel uncomfortable), the same as for the offensive odor substances. The range of odor index has been found to be 10-21 through the survey of the relation between odor intensity and odor index for almost all types of industry (Table 3).

Table 3. Relation between Odor Intensity and Odor Index

Odor intensity Range of odor index
2.5 10 - 15
3.0 12 - 18
3.5 14 - 21
The odor index has its advantage to be closer to the human sense of smell. The regulation by oder index can be effective for, for example, composite odor, on which that by specified offensive odor substances is not expected to bring about sufficient regulation effect.
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