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Технически университет - София

Abstract: This paper presents the parallel implementation and numerical evaluation of the Danish Eulerian Air Pollution Model (UNI-DEM) and its variant SA-DEM, designed for sensitivity analysis of the model, as well as certain critical parts of it. The model solves a system of partial differential equations describing advection-diffusion transport, chemical reactions, emissions, and deposition using operator separation, robust time-stepping schemes, and domain decomposition for MPI-based execution. Scalability experiments were performed on two supercomputers-IBM MareNostrum III (BSC) and Discoverer (Sofia Tech Park)-using a unified test. (480 × 480 grid, 35 species, "t = 90 s). The results show almost perfect scaling for the chemical stage and communication-limited scaling for the transport stage, with superlinear speedup observed at low core counts due to cache effects. A global sensitivity analysis was conducted for 12 kinetic parameters using Sobol dispersion-based indices calculated by several MC/QMC algorithms, such as MSS-1, MSS-2, MSS-2-C, VDC2, FIBO, and OPTL. The results show that the combination of advanced atmospheric modelling, high-Throughput computing, and quasi-Monte Carlo techniques provides both computational efficiency and reliable parameter ranking, supporting model downscaling and scenario-based air quality assessment.

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