Investigation of atmospheric nitrate and ammonium and their impact on air quality and climate in GMI

The capability to simulate nitrate and ammonium aerosols has been developed in NASA GMI model by implementing a thermodynamic equilibrium model that treats gas and aerosol multiphase chemical equilibrium reactions in a SO4-NO3-NH4- H2O system. Nitrate and ammonium can influence air quality and ecosystems substantially, and their importance will be increasing in the future due to the predicted increase of nitrogen emissions. An immediate outcome from the work is the possibility to improve tropospheric O3 simulation. Currently, the model treats HNO3 solely as a gas phase tracer. This semi-volatile species now partitions between gas and aerosol phases, and the tracer in each phase is subject to different chemical and physical processes. A preliminary analysis has been conducted by comparing results simulated with and without new nitrate package and by comparing model results with the ground station observations from CASTNET and EMEP.