Abstract
The Urban Heat Island (UHI) is a well-known phenomenon concerning an increasing percentage of the world’s population due to the growth rates of metropolitan areas. Given the health and economic implications of UHIs, several mitigation techniques are being evaluated and tested. In this study, we consider the use of highly reflective materials for urban surfaces, and we carried out numerical experiments using the Weather Research and Forecasting model coupled with the CHIMERE model in order to investigate the effects of these materials on the meteorology and air quality in the urban area of Milan (Italy). Results show that an increase in albedo from 0.2 to 0.7 for urban roofs, walls and streets leads to a decrease in UHI intensity by up to 2–3 °C and of the planetary boundary layer (PBL) height of about 500 m. However, the difference of PM10 and ozone between urban and surrounding areas increases by a factor of about 2, attributable to the reduction of PBL height and wind speed and to the increased reflected solar radiation that may enhance photochemical production during the daytime. Therefore, if anthropogenic emissions are held at the same levels, the potential benefit to the UHI in terms of thermal discomfort may have negative repercussions on air quality.
Highlights
An Urban Heat Island (UHI)—an urban area that is warmer with respect to the surrounding rural areas—is a well-known issue concerning urban environments
This study provides a first evaluation of strategic choices for a healthier city of Milan in the context context of climate change adaptation and mitigation
We investigated the effect of the use of highly highly reflective materials covering urban surfaces on meteorology and air quality
Summary
An Urban Heat Island (UHI)—an urban area that is warmer with respect to the surrounding rural (or suburban) areas—is a well-known issue concerning urban environments. Green roofs (covered with vegetation) and cool materials (characterized by high values of albedo and emissivity) are being increasingly used, and their effectiveness in reducing average and peak ambient temperatures has been demonstrated [13]. The impact of these techniques on atmospheric composition has been investigated [14,15]. Work, we used the offline WRF/CHIMERE model in order to isolate the effect of changed surface albedo in the city on meteorological and air quality variables, without the direct or indirect feedback of pollutants on dynamics and radiation. We consider two different scenarios for the increase in albedo values, while in [16] a single high-albedo was run for the roofs and facades scenario
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