Examination of the Evolution of Urban Plumes using MAPS (Model for Aerosol Process Studies)

MAPS (Model for Aerosol Process Studies) is an aerosol box model which uses sectional modeling to simulate gas and aerosol physical and chemical processes. Condensation, evaporation and nucleation of multicomponent aerosols are modeled, as well as gas phase photochemistry and aerosol phase aqueous chemistry. This model is based on the urban airshed model developed by Wexler et al. (1994), but has been enhanced to include external mixtures and aqueous phase chemistry, as well as an upgraded nucleation model and thermodynamics package. MAPS has been used to simulate the evolution of urban plumes, and compare this simulation to data taken from Mexico City (Project Azteca) and downwind of the Indian subcontinent (INDOEX- Indian Ocean Experiment). An ensemble of runs has been conducted to generate simulated aerosol compositions to compare to aerosol measurements obtained during Project Azteca (November, 1997). Using an ensemble of runs allows an evaluation of the initial conditions required to match the measured results, and to study the aerosol evolutionary processes under a variety of conditions. Another ensemble of runs was conducted to compare model results to aerosol measurements taken over the Indian Ocean during INDOEX. This simulation allowed an evaluation of the evolution of urban aerosols as the urban plume mixes with clean marine air downwind of the urban source.