Green soap. A calculation model for improving outdoor air quality in urban contexts and evaluating the benefits to the population’s health status

Regarding environmental sustainability, the encyclical “Laudato si” considers cities as living laboratories of nature-based solutions, capable of protect and promoting the population’s health status, as well improving sustainable land use and biodiversity. Densely-built urban contexts are affected by high levels of outdoor air pollution, coming from smog and fine particles, caused by vehicular traffic and the combustion processes of buildings’ heating systems. These pollutants cause several health issues, such as asthma, inflammatory and degenerative diseases and respiratory, cardiovascular and stress-related illnesses. At the same time, green areas are capable of absorbing toxic substances and of filtering polluted air. Taking into account the lack of green areas in urban environments, green roofs are delivering excellent alternatives for future implementations. A calculation model, named Green SOAP (Green Solutions for Outdoor Air Pollution), has been developed that quantifies green roofs’ capability to reduce air pollutants, with positive benefits on the environment, the population’s health status and the economic sustainability of the National Healthcare System. The research work has been structured in three macro-phases. A preliminary phase takes care of the state-of-the-art definition, through comparison with reference scientific bibliography; the proposal phase concerns the calculation model’s development; and the implementation phase consists of the application of Green SOAP in the “Città Studi” neighborhood, a case study identified in the city of Milano. The calculation-model application, according to the percentages defined by the morpho-typological analysis of the buildings, has shown that, with the new green roofs’ construction, it’s possible to reduce the pollutants approximately as high as 18.09 μg/m3of PM10, 13.56 μg/m3of PM2.5 and 7.24 μg/m3of O3each year. Nowadays, Green SOAP is being implemented within several contexts to verify its consistency and to increase the sample of case studies.