"Process weight rate" means the average total weight of all materials, not including any gaseous, liquid or solid fuels, moisture or combustion air, introduced into any manufacturing, industrial or combustion process that may result in the emission of any regulated pollutant to the ambient air, computed on an hourly basis, and shall be expressed in terms of weight per unit of time.
06- 096 C.M.R. ch. 100, § 140