218 Chapter 9
alter the pattern from place to place as, for example, industry is regulated to dif-
ferent parts of the urban system. Likewise, as release of pollutants is increas-
ingly from high chimneys,the distribution of pollutants will become more
dispersed, but increase in magnitude. This form of release tends to ‘export’
the effects of pollution from its local area of generation. Models, such as the
above at the macro-scale are important in identifying long-term and spatially-
wide trends betweenvariables.
Macro-scale patterns do not, however, help in understanding how the effects
of environment are mediated at the local level and how they interact with both
material and process to produce place-specific degradation forms and rates.
At the micro-scale, variations in environment can be vital. The exposure of a
surface, for example, can determine the amount of pollution it receives, the
magnitude and intensity of rainfall upon it (or if any reaches it at all), as well
as the rate and duration of drying. Figure 4 illustrates how an architectural
detail could influence the microclimate around it and so produce distinct
microenvironments that could accelerate or retard weathering by different
weathering agents.
Potential drip zone
Zone of high relative humidity
Sheltered from rainfallExposed to rainfall
Dissolution and
removal of weathering
productsRunoff zoneRunoff zoneSheltered from rainfall
Zone of high relative humidity
Relative stable air
Exposed to rainfall
Dissolution and removal of
weathering products
Saturation of flow if sufficient flow distanceDeposition zone for sediment
and potential ponding area for
rainfall/runoffZone of runoff impactFigure 4Microenvironment and variations in factors significant to weathering