Tuesday, 11 January 2005: 11:30 AM
A coupled dynamics-chemistry-aerosol column model for the lower troposphere
We coupled a 1 D PBL model with a 2.5 level turbulence closure model based on the K-E theory to (1) a photochemical model with 72 species, 132 thermal reactions, and 52 photolysis rates to calculate the evolution of aerosol precursors and (2) the MAD-SORGAM aerosol module to calculate the evolution of the aerosols within the PBL. The model now includes higher-order closure terms for chemical trace gases to account for the effects of turbulent mixing on the evolution of the trace gases and aerosols. The base version of the model has full representation of NOx, Ox, HOx, CH4, SOx, and CO chemistry and nonmethane hydrocarbon (NMHC) reaction scheme used is based on RACM. The complete chemical scheme represents 79 different gas species, 214 thermal reactions, and 32 photolysis reactions. The photolysis rate calculations are performed by using the FAST J, designed for calculating photolysis rates mainly in the troposphere and also effects of clouds and aerosol layers of various types on calculated photolysis rates. The MAD code represents aerosol size distributions as three different size modes (nucleating, accumulation, and coarse), with a log-normal function describing the size distribution within each mode. The SORGAM code represents the formation and simulates the production of semivolatile organic compounds and their gas-particle partitioning. A total of 28 different components are modeled in the three size modes. The model resolves the chemical compositions of aerosols derived from sulfur, nitrogen oxides, ten different hydrocarbons, sea salt, and soil dust. In addition, the 1 D model calculates dry deposition losses for some gases and aerosols that are prescribed at fixed values at the model surface for the course of the simulation. Emissions at the surface can be prescribed for a number of precursor gases and aerosols. This model is now being tested for evaluating the aerosol module. Preliminary results from this coupled model will be presented.