Review and Critical Analysis of International UHI Studies

A study in France sought to find out through simulation what impact the Paris urban heat island
had on the distribution or air pollutants. The simulation was carried out in an anticyclonic
weather system. The simulations were conducted with the Meso‐NH atmospheric model linked
to a chemistry module. Meso‐NH is a non‐hydrostatic mesoscale atmospheric model allowing
two‐way nesting simulations. The model is initialized and forced at the lateral boundaries every 3
hours by a forecast model for dynamic parameters and a global chemical transport model for all
chemical species. Two simulations were performed, one in an urban location using the town
energy balance urban surface scheme, the other is performed without it representing a more rural
location. The results of the simulation show that at night the UHI is very apparent and is
advected by Paris’ south‐westerly winds. During the daytime the urban simulation’s
temperatures are still increased which has an impact on pollutant concentrations. In both
simulations the turbulent flux is the primary driver for the spatial distribution of the ozone
plume and NOx concentrations [139].
The USDA Forest Service created a model to calculate how much air pollution could be reduced
by the introduction of urban trees and shrubs. The model was fed with hourly meteorological
and pollution concentration data and urban tree cover data over 55 cities across the US. The
results of the simulation showed variation across the cities studied. The simulation calculated
that urban trees in the US could remove 711,000 metric tonnes of urban air pollutants, O3, PM10,
NO2, SO2, CO [013].
Taha discusses the heat island’s impact on air quality, and a using uMM5 and CAMx models
with particular reference to ozone. The study also models albedo increase and its impact on air
temperature and air quality. The results of the CAMx simulation show that the model captures
the higher downwind concentrations but not the downwind concentrations of the downtown
area. Overall the model shows that the albedo increases of the mitigation strategy reduce levels of
ozone, there are however, some signs of an increase, although only in short intervals. Decreases
of around 5‐10 parts per billion (ppb) are recorded and the average daily maximum 8 hours could
be decreased by up to 13% [049].
3.2.4 Simulations of Energy Use & Peak Power Impacts
Only one paper discussed a simulation that was focused on energy consumption without the
influence of mitigation technologies, this was undertaken in Tokyo, Japan [062]. Six studies were
reviewed on energy consumption as a result of mitigation measures, four in North America [168,
033, 171, 012] and two in Asia [031, 022].
The models used were predominantly building simulation models (often called BEM),
particularly DOE‐2.1E. A program called RADCOOL, another building simulation, was used in
one study but proved to be limited in scope. Where other influential factors were simulated MMs
and CMs were used.
The following paragraphs provide an overview of some of the simulations undertaken and their
results:
Review and Critical Analysis of International UHI Studies
Page 28