Different numerical algorithms have been used in air quality PM models to minimize numerical diffusion when simulating aerosol dynamic processes with a sectional representation of particle size. We evaluated two numerical algorithms (the Bott and the spline interpolation algorithms) that are used in 3-D PM models to simulate particle condensational growth and gas/particle mass transfer. For simulation of condensational growth, the Bott algorithm causes some upstream numerical diffusion for the fine particle size range (with diameter < 0.1 micro meter), whereas the spline interpolation algorithm leads to significant numerical diffusion over a large particle diameter range of 0.01- 2.5 micro meter. For simulation of gas/particle mass transfer, the two algorithms predict similar particle size distribution for cases without NaCl, however, they predict significantly different particle size distribution for cases with NaCl.
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