It is common sense that clean air is essential for the well-being of humans, animals and plants. But high traffic density, fuel combustion, biomass burning and industries are creating a mixture of air pollutants that are major risk to health.
China tops the WHO list for deadly outdoor air pollution so far, but even in Europe there are nearly 500,000 premature deaths each year. Decades of industrialisation and rapid economic growth have led several countries to experience air acidification, harming vegetation and buildings.
Even when the emission situation is not that severe, the combination of pollutant sources and poorly aerated areas such as narrow street canyons can quickly lead to the accumulation and local enrichment of air pollutants in excess of air quality standards. Moreover, it is known that even low pollutant concentrations can increase allergic responses e.g. to pollens.
The pollutant dispersion model of ENVI_MET allows the synchronous release, dispersion and deposition of up to six different pollutants including particles and passive and reactive gases. Sedimentation and deposition on surfaces and vegetation is taken into account as well as the photochemical reaction between NO, NO2 and Ozone (O3) and the release of (B)VOC through plants.
The results can be used to better understand the dynamics of local pollutant dispersion and help to develop urban streetscapes and green infrastructure for improving air quality and human well-being.
In the context of urban microclimates, thermal
comfort is the key indicator to describe people´s subjective experience of temperature in open spaces. It summarises the impact of sun, wind, air temperature and humidity on thermal sensation.
If the human body is not able to compensate for hot or cold environmental conditions through thermoregulation, thermal discomfort arises and the actual environment is perceived to be too warm or too cold. Unpleasant thermal conditions in urban areas are one of the main reasons why people prefer to live in the outskirts of the city rather than in the centre. This leads to a continuous expansion of urbanised areas, known as urban sprawl. There are many environmental and economic drawbacks associated with this sprawl effect, of which land consumption and traff ic congestion are probably the most obvious.
Sustainable urban open spaces must therefore have a design where the expectations and wishes of the potential users meet with the functional requirements of the city structure. Hence, assessing the microclimate conditions of an urban space means finding out how pedestrians feel under given climatic conditions – especially their thermal comfort and wind comfort – and how this Iimpacts behaviour within the urban structure.
In addition, adequate thermal conditions can play a key role in the economic success of outdoor facilities such as cafés, shopping streets or recreational spaces. Different thermodynamic models in ENVI_MET allow a holistic evaluation of steady state and transient thermal comfort conditions.