How to increase the simulated concentration of nitrate?

Hi All,
I used CMAQ5.3.3 to simulate nitrate, MECH is saprc07tic_ae7i_aq. After the simulation, it was found that the nitrate concentration was much lower than the observation, and the nitrate concentration was very low during the day, which was very different from the observation. How can I modify the model to increase the nitrate concentration? Attached is a comparison of simulated nitrate and observed results.(Black is the observed and red is the simulated )
Can anyone give me some advice?

Hi xue,
Can you please provide a bit more information about your application, e.g., your model domain, horizontal and vertical grid resolution, simulation dates, source of meteorology and emissions inputs, science options that you are using. If you could please also share the source of your observations, e.g., are you evaluating at a single location or across multiple monitoring sites. Evaluation results can vary quite a bit depending on the model inputs that are used, model configuration, and the location and time period being studied. To make changes to the model that would improve model performance you would first want to see if you can diagnose the cause(s) of the model underestimation for your particular application. This is often challenging but we may be able to offer some suggestions once we know more about your study.

Maybe you could check your traffic emissions first. The temporal profiles seems odd. You could also take a look at.

When I calculated the nitrate concentration in summer, I also found that the particle nitrate was low and the gas HNO3 concentration was high. Is there a problem with the gas-particle balance

[Looking forward to your reply!