Numerical Simulation of Atmospheric Photochemistry in a Laminar-Flow Tube Reactor

The climatological impact and chemical characteristics of atmospheric aerosols remain very uncertain. The latest step in this field is the experimental use of UV-lit gas-phase tube reactors to simulate days to weeks of atmospheric photochemistry. These reactors have typically been modeled as plug-flow reactors. We have constructed a more detailed model to describe the new laminar-flow tube reactor constructed by the Seinfeld Group. This model assumes radial symmetry and takes into account the non-uniform velocity distribution in the tube’s flow. However, it ignores gas-phase diffusion since preliminary simulations indicated that it may not have a large effect. A numerical simulation of this model was constructed to consider the steady-state addition of an arbitrary number of reactants. Starting with a list of reactions and reaction rate constants, this simulation can generate an estimate of species concentrations for each species everywhere in the reactor. It does this by repeatedly solving an N-dimensional ODE for different reactor streamlines using backward differentiation formulae and Newton iteration. This allows for the simulation of very large and very stiff kinetic systems within the reactor. Experimental evaluation of the model’s accuracy is necessary. Diffusion may also be considered in the future.