Nitrate is an important atmospheric aerosol component and impacts on air quality, climate, and ecosystem. Nitrate will be more important in the future climate study owing to projected growth of future population and energy use. It has been concluded that aerosol nitrate has to be included to the current suite of aerosol types (sulfate, BC, OC, dust and sea salt) in the next generation of climate models by the NARSTO final report [http://www.narsto.org/sites/narstodev.ornl.gov/files/AerosolProcesses_Final.pdf]. Nevertheless, unlike the other major atmospheric aerosol components, the simulation of aerosol nitrate from AeroCom models has not yet been extensively evaluated. This work attempts to strengthen the nitrate evaluation and will investigate it from three aspects:

1. Address the diversity of the nitrate simulation by the AeroCom multi-models and diagnose the driving process for the diversity;
2. Explore the uncertainty of the model nitrate simulations constrained against various measurements from ground station networks, aircraft campaigns, and satellite retrievals;
3. Investigate how the formation of nitrate changes in different models in response to the perturbation on key precursors and factors that determine the nitrate formation.