Modeling The Effects of Heterogeneous Reactions On Atmospheric Chemistry And Aerosol Properties During INTEX-B Field Campaign

A new aerosol module is developed for the STEM model (the Sulfur Transport and dEposition Model) to better understand the chemical aging of dust during long range transport and assess the impact of heterogeneous reactions on tropospheric chemistry. In the new aerosol model, a non-equilibrium (dynamic or kinetic) approach to treat gas-to-particular conversion is employed and a new numerical method solving the aerosol dynamics equation is introduced into the dynamic aerosol model for its improved computational efficiency and high accuracy. Laboratory studies show that the impacts of relative humidity on heterogeneous reactions are significant, which is investigated in the modeling. The new version of STEM model is utilized to explore the observations from the Intercontinental Chemical Transport Experiment - Phase B (INTEX-B). The new dynamic approach for gas-to-particular conversion and RH-dependent heterogeneous uptake of HNO3 improve the model performance in term of aerosol predictions under different conditions. It is shown that these improvements change the modeled nitrate and sulfate concentrations, but also modify their size distributions significantly.