Examining the sensitivity of MM5–CMAQ predictions to explicit microphysics schemes and horizontal grid resolutions, Part II—PM concentrations and wet deposition predictions

This part II paper first evaluates the simulated concentrations and wet deposition amounts of NH4+, NO3−, and SO42− using observations from several networks, then examines their sensitivities to four explicit microphysics schemes: Reisner 1 (R1), Reisner 2 (R2), Dudhia simple ice (SI), and Hsie warm rain (WR). For baseline simulation with R1, the concentrations of NH4+, NO3−, and SO42− are underpredicted in August. Concentrations of SO42− are underpredicted and those of NH4+ and NO3− are overpredicted in December. The wet deposition amounts of NH4+ and SO42− are overpredicted but those of NO3− are underpredicted in August. The wet deposition amounts of NO3− and NH4+ are overpredicted but those of SO42− are underpredicted in December. The simulated wet deposition amounts are sensitive to various schemes, which are most evident in December, with the best results for NH4+ and NO3− by WR and the best for SO42− by SI. A correlation exists between wet deposition amounts and precipitation in both months, with stronger magnitudes in August. Conversely, in December, as the correlation with precipitation decreases, that with aqueous-phase concentrations increases. These results are consistent with meteorological conditions since the summer convective precipitation events having larger intensities and therefore the meteorological forcing is expected to dominate August correlations. As these intensities decrease in December, the chemical forcing becomes more influential.