AIR POLLUTION – MONITORING MODELLING AND HEALTH

Urban Air Pollution 23
cells 40 x 40 grid points) and domain 4 (resolution of 1 km x 1km cells 34 x 30 grid points).
The domain 4 includes main part of HCMC. The results from nesting procedure for initial
and boundary conditions are used over this domain. For the largest domain (domain 1), the
initial and the boundary conditions are interpolated from 6-hourly data from National
Centers for Environmental Prediction (NCEP). In vertical position the grids extend up to
10,000 m, with 30 levels. The vertical resolution is 10 m for the first level, and then it is
stretched up to the top of the domain at 1000 m [(grid stretching ratio equal to 1.2) (Martilli
et al. 2002)]. Land use data obtained from the U.S. Geological Survey (USGS) is used as
input for the simulations. For obtaining more realistic initial conditions, a pre-run of one day
is computed for the meteorological simulations.
Air quality model
The air quality model used for this research is the Transport and Photochemistry Mesoscale
Model (TAPOM) (Martilli et al . 2003; Junier et al . 2004) implemented at EPFL and at the
Joint Research Centre of Istituto Superiore per la Protezione e la Ricerca Ambientale
(ISPRA). It is a transport and photochemistry three-dimensional Eulerian model. It is based
on the resolution of the mass balance equation for the atmospheric substances. This equation
includes the advection by the mean wind, the vertical diffusion by the turbulence, the
chemical transformation by reactions, the dry deposition and the emissions. The chemical
transformations are simulated by using the RACM (Stockwell et al. 1997), the Gong and Cho
(Gong et al. 1993) chemical solver for the gaseous phase and the ISORROPIA module for
inorganic aerosols (Nenes et al. 1998). The transport is solved using the algorithms
developed by Collella and Woodward (Collella et al. 1984). Then this algorithm has recently
developed by Clappier (Clappier et al. 1998). Now there are a lot of atmospheric models
uses this algorithm. The photolysis rate constants used for chemical reactions are calculated
using the radiation module TUV which is developed by Madronich (Madronich et al. 1998).
In vertical position, the grids extend up to 7300 m with 12 levels. The vertical resolution is 15
m for the first level, and then it is stretched up to the top of the domain at 2000 m (grid
stretching factor of 1.2 for lower and 1.6 for upper layers of the grid).
domain 1
domain 4
Fig. 10. Topography of South of Vietnam and description of simulated domains (left panel).
The central black square (shown in left panel) used for the air quality simulation domain
(right panel). (Source: http://edcdaac.usgs.gov/gtopo30/gtopo30.html (online & free
downloading)).