Mass conservation in the Community Multiscale Air Quality model

Mass conservation errors were discovered when the Community Multiscale Air Quality (CMAQ) model (version 4.3) was coupled with the Fifth-Generation PSU/NCAR Mesoscale Model (MM5). These errors can be severe particularly over complex terrain. A recent correction made to the vertical advection module (in version 4.4) reduces the mass conservation errors, but does not completely eliminate them. This means that the method of renormalizing concentrations according to air density, which is currently applied to address the inconsistency problem, is not an ideal solution. Reconstruction of the wind fields by adjusting the vertical wind is proposed as a simple remedy to make CMAQ strictly mass conservative.