Correcting RADM's Sulfate Underprediction: Discovery and Correction of ModelErrors and Testing the Corrections Through Comparisons against Field Data

摘要

A serious underprediction of ambient sulfate SO4(sup -2) by two comprehensive,Eulerian models of acid deposition, the Regional Acid Deposition Model (RADM) and the Acid Deposition and Oxidant Model (ADOM), was found in the National Acid Precipitation Assessment Program phase of the Eulerian Model Evaluation Field Study (EMEFS) model evaluation. Two hypotheses were proposed to explain the cause of the underprediction in RADM: insufficient SO4(sup -2) production by nonprecipitating convective clouds and insufficient primary SO4(sup -2) emissions. Modifications of the RADM cloud and scavenging module to better simulate nonprecipitating cumulus clouds are described in detail. Three contrasting pairs of tests using data from the EMEFS were applied to these hypotheses: source vs. downwind regions; mid summer vs. late summer seasons, sunny-dry vs. cloudy-wet synoptic types. The SO4(sup -2) emissions hypothesis, tested by artificially boosting SO4(sup -2) emissions, fared better than expected but was rejected because of its poor performance on the regional and seasonal contrast tests. The RADM nonprecipitating cumulus modification successfully captured the seasonal and the late summer synoptic contrasts but improvement is still needed for the regional and mid summer synoptic contrasts.