Modeling atmospheric aerosol dynamics: Condensation, nucleation, and application.

摘要

Atmospheric aerosols have been shown to have a negative effect on human health, visibility, and to play a significant role in the global energy balance. Three-dimensional chemical transport models that can accurately predict atmospheric aerosol concentrations are necessary for the development of cost effective emission control strategies. Several factors limit the effectiveness of these models. First, these models are computationally intensive, with aerosol processes taking up a large portion of the total CPU time. Furthermore, some important atmospheric processes, such as aerosol nucleation and organic aerosol formation and growth, are not well understood. A third factor affecting the performance of the models is the quality of the inputs (i.e., meteorology and emissions). In this work, several of these issues are explored.; First, an improved method of solving the condensation/evaporation equation is presented. Condensation of gases (H2SO4, NH 3, HNO3, low vapor pressure organic, etc.) onto existing aerosols can account for a significant portion of fine particulate matter. The trajectory-grid method, used for solving the transport equation, has been adapted for solving the condensation/evaporation equation and preliminary results have shown it to be fast and accurate in solving condensation/evaporation in simple systems (one component, etc.). Here, the trajectory-grid method is modified for implementation into one-dimensional and three-dimensional chemical transport models.; Next, particle formation events in the eastern United States are investigated in a modeling study. Although recent observations show that nucleation is widespread in the eastern United States and other parts of the world, the corresponding pathways remain uncertain. Combining extensive field measurements in Pittsburgh, PA with an aerosol dynamics and chemistry model assuming ternary NH3-H2SO4-H2O nuclei formation, excellent model-measurement agreement and predictive capability is achieved.; Finally, a three-dimensional chemical transport model, PMCAMx+, is developed and applied to a PM episode in the eastern United States. PMCAMx+ is incorporated into the existing three-dimensional chemical transport model, CAMx, with the addition of three detailed aerosol modules developed at Carnegie Mellon University. The modules deal with the processes of inorganic aerosol condensation, organic aerosol formation and growth, and aqueous phase chemistry, with the overall goal of maintaining good accuracy while improving efficiency. (Abstract shortened by UMI.)