Model Urbanization Strategy: Summaries, Recommendations and Requirements - Meteorological and Air Quality Models for Urban Areas - page 143

pollution components have complex and combined effects on human health (e.g.,
hot spots, heat stresses); and pollutants, especially urban aerosols, influence climate
forcing and meteorological events (precipitation, thunderstorms, etc.). The online
integration of mesoscale meteorological models and atmospheric aerosol and chem-
ical transport models enables the utilization of all meteorological 3D fields in ACT
models at each time step and the consideration of feedback among air pollution (e.g.,
urban aerosols), meteorological processes, and climate forcing (e.g., WRF-Chem:
Grell et al., 2005; Enviro-HIRLAM: Baklanov et al., 2008).
Chemical species in the atmosphere, such as CO 2 and ozone act as green-
house gases to influence weather and atmospheric processes. Aerosols such as sea
salt, dust, primary and secondary particles of anthropogenic and natural origin are
also airborne and contribute to atmospheric processes in a complex manner. Some
aerosol components (black carbon, iron, aluminum, and polycyclic and nitrated aro-
matic compounds) warm the air by absorbing solar and thermal-infrared radiation,
whereas others (water, sulphate, nitrate, and most organic compounds) cool the air
by backscattering incidental short-wave radiation into space. The effects of urban
aerosols and other chemical species on meteorological parameters have many dif-
ferent pathways (direct, indirect, semi-direct effects, etc.) that these online, coupled
modeling systems are capable of addressing.
15.5 Database and Evaluation Aspects of Urbanized Models
It is evident that there are a large range of applications that involve an urban focus.
Moreover, given the wide range of model complexities, operational and data input
requirements, and diverse applications, we find that there is no “one-size-fits-all”
modeling approach that addresses the wide range of modeling objectives. Thus,
for urban applications, the fitness-for-purpose concept is a relevant and important
consideration. In this survey, we have identified a number of considerations; some
of the major ones are outlined below.
15.5.1 Database Requirements
Models of urban areas will be required to provide reliable predictions at fine 3D
resolution of turbulent exchanges, air flow and thermodynamic characteristics. To
meet these requirements, parameterizations are being developed and implemented
with varying degrees of detail in terms of features and sophistication relative to the
actual features of individual cities. One limitation to the degree of complexity in the
model parameterizations is the availability of appropriate morphology information.
For operational needs, the requirements are fulfilled using specifications associated
with limited numbers of urban land use categories, each with specified surface
properties such as roughness, displacement lengths, albedo, moisture availability,
and thermal properties. For research and development applications, models that can