Keywords: atmospheric pollution, bloc distribution, MPI library, PC clusters, chemical pollutant transformation, simulation, parallel computing, chemistry transport model
Atmospheric dispersion and chemical pollutant transformation simulated with parallel calculations using two PC clusters
The numerical simulation of atmospheric pollution needs long calculation times, mainly due to the chemistry involved, for example in photochemical episodes for which a lot of species and reactions must be taken into account. Parallelisation can reduce these calculation times. In this work, we have made parallel computation with a Eulerian transport/chemical model with the MPI communication library. We used two PC clusters, each PC having similar CPU and memory capacity but being connected in a network with different management systems. Three cases have been simulated, an inert one, one with a simple chemical scheme (nine species and nine reactions) and the last one with a detailed chemistry mechanism (121 reactions and 63 species). With no chemistry, the efficiency falls rapidly due to communication between neighbouring blocks. With chemistry, however, the efficiency is better, and we note that the greater the number of species taken into account the higher the efficiency. This is easily explained by the absence of messages passing in chemistry parts of the program. The present simulations are representative of atmospheric pollution episodes. The efficiency for calculations with photochemistry and using eight runs is about 50%, which corresponds to a four-fold increase in speed, which is interesting only for long-term applications.