a) "Dispersion technique" means any technique that attempts to affect the concentration of a pollutant in the ambient air by:

1. 1) Using the portion of a stack that exceeds good engineering practice stack height;
2. 2) Varying the rate of emission of a pollutant according to atmospheric conditions or ambient concentrations of that pollutant; or

3. 3) Increasing final exhaust gas plume rise by:

   1. A) Manipulating source process parameters, exhaust gas parameters, or stack parameters;
   2. B) Combining exhaust gases from several existing stacks into one stack; or
   3. C) Other selective handling of exhaust gas streams so as to increase the exhaust gas plume rise.

b) "Dispersion technique" does not include:

1. 1) The reheating of a gas stream, following use of a pollution control system, for the purpose of returning the gas to the temperature at which it was originally discharged from the stationary source generating the gas stream;

2. 2) The merging of exhaust gas streams when:

   1. A) The source owner or operator demonstrates that the stationary source was originally designed and constructed with such merged gas streams;
   2. B) After July 8, 1985, the merging is part of a change in operation at the stationary source that includes the installation of pollution controls and is accompanied by a net reduction in the allowable emissions of a pollutant. This exclusion from the definition of dispersion techniques shall apply only to the emission limitation for the pollutant affected by the change in operation; or
   3. C) Before July 8, 1985, such merging was part of a change in operation at the stationary source that included the installation of emissions control equipment or was carried out for sound economic or engineering reasons. When there was an increase in the emission limitation or, in the event that no emission limitation was in existence prior to the merging, an increase in the quantity of pollutants actually emitted prior to the merging, the Agency shall presume that merging was significantly motivated by an intent to gain emissions credit for greater dispersion. Absent a demonstration by the source owner or operator that merging was not significantly motivated by such intent, the Agency shall deny credit for the effects of such merging in calculating the allowable emissions for the source;
3. 3) Smoke management in agricultural or silvicultural prescribed burning programs;
4. 4) Episodic restrictions on residential wood burning and open burning; or
5. 5) Techniques under subsection (a)(3) that increase final exhaust gas plume rise when the resulting allowable emissions of SO₂ from the stationary source do not exceed 5,000 tpy.