Urban heat island

Urban Heat Island Urbanized area that experiences higher temperatures than surrounding... 

Fig. 17-21. Urban heat island (light regional wind).

There have been some indications, although controversial, of increased precipitation downwind of major metropolitan areas. Urban addition of nuclei and moisture and urban enhancement of vertical motion due to increased roughness and the urban heat island effect have been suggested as possible causes. 

Surface topography can affect the local wind patterns one example is the onshore and offshore breeze, and another example is the heat island over large urban areas. Another manmade effect is the generation of mechanical turbulence caused by the nonuniform height of buildings in a city. We will discuss this effect in more depth later on. 

Contaminant Emissions in Urban Areas 195 6.8.2 Residential Density and Urban Heat Islands... 

The urban heat island effect has implications for chemical emissions in several ways. Elevated temperatures increase the consumption of energy for air conditioning and other cooling systems, with attendant increases in fossil fuel combustion-related contaminants (Cardelino et al., 2001 Adams, 1999). Increased ambient air temperatures also increase volatilization of POPs such as PCBs, PCNs and PBDEs from urban sources (Priemer and Diamond, 2002 Helm and Bidleman, 2003). 

There are many unanswered questions regarding chemical interactions and fate processes. What is the composition and impact of chemical interactions given the complex mixture of chemicals emitted and found in urban matrices (e.g. enhanced rates of chemical reaction and a wider range of transformation products) What are the roles of urban form and management practices in mediating transport dynamics (e.g. the implications of stormwater management systems on total chemical fate) Furthermore, what role do different types of urban development patterns and heat island effects play with respect to contaminant fate Does the simplified vegetative community that is dominated by exotic species influence the rate at which chemicals are processed or accumulated ... 

Stone, B., Rodgers, M.O. (2001) Urban form and thermal efficiency - How the design of cities influences the urban heat island effect. Journal of the American Planning Association, 67(2) 186-198. 

These do not account for specifically urban dynamics and energetics and their impact on the ABL characteristics (e.g. internal boundary layers, urban heat island, precipitation patterns). 

Another local effect, in this case due to surface cover, is the urban heat island. Rapid heating of urban pavements and buildings occurs during the daytime because of the high absorbance of constructed surfaces and the absence of cooling from evapotranspiration. At night, rural areas cool more effectively than urban areas because of the relatively unobstructed exposure of the land surface, in contrast to the impediment to heat radiation presented by tall, closely spaced buildings. As a result, daily minimum and maximum... 

Anthropogenic heat fluxes, including the so-called urban heat island ... 

PBL-scale effects, e.g. sea breezes, urban heat islands and katabatic flows ... 

Figure 14. The urban heat island. Space heating and other human activity generate temperature gradients that can give rise to thermal convection cycles (after Oke, 1987)...

Drainage pavements coated with polymer-modified paste containing photocatalyst (ana-tase-type titanium dioxide) (which effectively decompose car exhaust gases with nitrogen oxides on road surfaces by the action of the photocatalyst and prevent air pollution) Special semiflexible pavements with water retentivity, executed by grouting the voids of open-graded asphalt concrete with polymer-modified paste containing superabsorbent polymers to prevent a heat island phenomenon in urban areas... 

Balling Jr., R. C., Cerveny, R. S. and C. D. Idso (2002) Does the urban CO2 dome of Phoenix, Arizona contribute to its heat island Journal of Geophysical Research Letters 28, 4599-4601... 

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