Reactive plume model: Effect of stack exit conditions on gas phase precursors and sulfate formation

A simple form of a carbon-bond smog mechanism has been introduced into a complete set of plume conservation equations. The conservation expressions for mass, momentum, energy and component species have been solved numerically for typical source and neutral or adiabatic ambient conditions to simulate the homogeneous gas phase chemistry for approximately two hours of travel time downwind from the stack exit. The influence of stack exit conditions including the ratios of momentum-to-buoyancy length l_m/l_b, source-to-ambient velocity R and mixing-to-reaction time τ are demonstrated.It was found that homogeneous processes in the plume near-field do not significantly contribute to the overall conversion of SO₂ to SO²⁻₄. In the far-field maximum sulfate formation rates of 2.3% h⁻¹ were predicted for clear summer noon hours, consistent with plume measurements. Variation of stack exit conditions were found to have little effect on the maximum SO₂ conversion rate or the peak OH radical concentration where local HC/NO_x ratios between 16 and 22 were predicted. Parameter changes resulting in greater ambient entrainment rates, however, were found to shift the development of the radical pool closer to the source and to significantly increase the total molar flux of plume sulfate.