CMAQv5.0.2 Aerosol updates

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Brief Description

Under cold conditions (approximately 210 K) the NO3 aerosol can become slightly negative in the i and j modes. In CMAQ 5.0.1 and earlier, this was initially corrected with a mass balance adjustment but because this was only done under the j mode loop and added the mass from the i mode into the j mode. This can continually add mass to the j mode and in the right conditions can crash the model with an ISOROPIA-II error or a photolysis error. aero_subs.F was corrected to apply the mass balance correction to both the i and j modes.

Significance and Impact

This correction resulted in a reduction of NO3 and HNO3 in the layers near the tropopause of the model simulation and, due to vertical transport from these layers to the surface, this results in approximately a 3% reduction in NO3 and HNO3 at the surface level and a similar reduction in wet deposition. These changes are larger over higher terrain where vertical mixing is more vigorous. Overall, this may increase the bias by approximately 3%-5% in ambient NO3 and HNO3 and NO3 wet deposition observations but also generally decreases the model error in these model variables.

Affected files





Jesse Bash, Atmospheric Modeling and Analysis Division, U.S. EPA