x
Foreword
domain (San Jose et al., 2008). Although models differ in their treatment of different
mechanisms and feedbacks, they all employ a similar framework and consist of the
same major modules:
Transport and diffusion
•
—calculating three-dimensional motion of gases
and aerosols in a gridded model domain
Gas-phase chemistry
•
—calculating changes in gaseous concentrations due
to chemical transformations
Aerosol
•
—calculating size distribution and chemical composition of aerosols accounting for chemical and physical transformations
Cloud/fog meteorology
•
—calculating physical characteristics of clouds
and fog based on the information from the meteorological model (or from
observations)
Cloud/fog chemistry
•
—calculating changes in chemical concentrations in
clouds/fog water
Wet deposition
•
—calculating the rates of deposition due to precipitation
(and, possibly, cloud impaction and fog settling) and the corresponding
changes in chemical concentrations
Dry deposition
•
—calculating the rates of dry deposition for gases and
aerosols and the corresponding changes in their concentrations
Consequently, the quality of the air pollution forecasts using such systems critically
depends on the adequacy in mapping emissions, representing meteorological fi elds,
and modeling the transport, dispersion, and transformation of chemicals/pollutants.
Various scientifi c developments now allow models to reasonably predict simple fl ow
situations within a factor of 2 or so.
What is more challenging is to predict episodes of high pollutant concentrations,
which may cause dramatic impacts on human health. Such situations, moreover, are
often induced by special situations, such as complex terrains, low winds, and very
stable stratifi cation causing shallow ABLs with low level of turbulent mixing. These
situations create problems for current methods and models to realistically reproduce
meteorological input fi elds.
The key physical mechanisms controlling concentrations of pollutants in the
atmosphere are advection, turbulent diffusion, wet and dry deposition, and gravitational settling. Their representation requires 3D fi elds of the wind velocity and direction, static stability (lapse rate), the ABL height (often called “mixing height”), basic
characteristics of turbulence (eddy diffusivities and velocity variances across the
atmosphere, and turbulent fl uxes of momentum, buoyancy, and scalars at the surface
and at the ABL outer boundary), and precipitation. Additionally, boundary conditions described by the basic physical and geometric characteristics of the surface (in
particular, the roughness lengths for momentum and scalars, and the displacement
heights) are very critical.
Most of the emissions are situated and most of the pollutants are dispersed within
the ABL, whose upper boundary (the layer at which the intensity of turbulence
strongly drops down) serves as a kind of a semi-impervious lid. Hence the mechanisms controlling concentrations strongly depend on the ABL turbulence, and, fi rst
© 2010 by Taylor and Francis Group, LLC
Foreword
domain (San Jose et al., 2008). Although models differ in their treatment of different
mechanisms and feedbacks, they all employ a similar framework and consist of the
same major modules:
Transport and diffusion
•
—calculating three-dimensional motion of gases
and aerosols in a gridded model domain
Gas-phase chemistry
•
—calculating changes in gaseous concentrations due
to chemical transformations
Aerosol
•
—calculating size distribution and chemical composition of aerosols accounting for chemical and physical transformations
Cloud/fog meteorology
•
—calculating physical characteristics of clouds
and fog based on the information from the meteorological model (or from
observations)
Cloud/fog chemistry
•
—calculating changes in chemical concentrations in
clouds/fog water
Wet deposition
•
—calculating the rates of deposition due to precipitation
(and, possibly, cloud impaction and fog settling) and the corresponding
changes in chemical concentrations
Dry deposition
•
—calculating the rates of dry deposition for gases and
aerosols and the corresponding changes in their concentrations
Consequently, the quality of the air pollution forecasts using such systems critically
depends on the adequacy in mapping emissions, representing meteorological fi elds,
and modeling the transport, dispersion, and transformation of chemicals/pollutants.
Various scientifi c developments now allow models to reasonably predict simple fl ow
situations within a factor of 2 or so.
What is more challenging is to predict episodes of high pollutant concentrations,
which may cause dramatic impacts on human health. Such situations, moreover, are
often induced by special situations, such as complex terrains, low winds, and very
stable stratifi cation causing shallow ABLs with low level of turbulent mixing. These
situations create problems for current methods and models to realistically reproduce
meteorological input fi elds.
The key physical mechanisms controlling concentrations of pollutants in the
atmosphere are advection, turbulent diffusion, wet and dry deposition, and gravitational settling. Their representation requires 3D fi elds of the wind velocity and direction, static stability (lapse rate), the ABL height (often called “mixing height”), basic
characteristics of turbulence (eddy diffusivities and velocity variances across the
atmosphere, and turbulent fl uxes of momentum, buoyancy, and scalars at the surface
and at the ABL outer boundary), and precipitation. Additionally, boundary conditions described by the basic physical and geometric characteristics of the surface (in
particular, the roughness lengths for momentum and scalars, and the displacement
heights) are very critical.
Most of the emissions are situated and most of the pollutants are dispersed within
the ABL, whose upper boundary (the layer at which the intensity of turbulence
strongly drops down) serves as a kind of a semi-impervious lid. Hence the mechanisms controlling concentrations strongly depend on the ABL turbulence, and, fi rst
© 2010 by Taylor and Francis Group, LLC