Reduced gas phase kinetic mechanisms for atmospheric plume chemistry

The subgrid-scale simulation of plume chemistry in three-dimensional air quality models can be computationally demanding. To minimize this computational burden, a reduced kinetic mechanism for the gas-phase chemistry of power plant plumes is developed and validated against a full chemical kinetic mechanism. This reduced mechanism simulates plume chemistry according to three stages of the plume evolution: (1) A first stage where plume radical concentrations are negligible and plume chemistry is limited to four major reactions during the day and two at night. (2) A second stage where plume concentrations of OH and NO3 radicals are sufficiently high to lead to significant formation of HNO3 and H2SO4 and which can be simulated with 30 reactions (or, alternatively, two different sets of 19 and 18 reactions for daytime and nighttime, respectively). (3) A third and final stage where VOC oxidation and O-3 formation become important, and the full chemical mechanism is required. For 10% accuracy in simulated plume concentrations, the reduced mechanism led to reductions in computational time of up to a factor of 3.