Breathe: Implementation of green barriers to mitigate air pollution in school playgrounds – case studies from UK and Argentina

Globally, more than 90% of children live in areas that exceed the World Health Organization air pollution limits. Simultaneously, evidence has shown that children are especially susceptible to suffer detrimental health effects caused by air pollution. Some of these health conditions include asthma exacerbation, bronchitis, or cognitive impairment. Innovative solutions that mitigate the risks to children’s health from air pollution are urgently needed. This thesis examined green (vegetated) barriers as a nature-based solution to air pollution in school playgrounds, where children spend a large part of their day. It intends to close the technical and application gaps for green barrier implementation. For this purpose, real-life green barriers were installed in two school playgrounds, in Sheffield, UK and in Buenos Aires, Argentina, and are the focus (case studies) of this research. Through the UK case study, the research aimed to 1) assess the air pollution mitigation potential of green barriers in school playgrounds considering the air pollution-vegetation interaction, 2) identify the co-benefits, trade-offs and disbenefits of green barrier implementation for school communities, and 3) understand the implementation process and practicalities of green barriers in school playgrounds. Additionally, through the Argentine case study, this research aimed to 4) identify barriers and solutions to green barrier implementation in school playgrounds in a Latin American context. Action research was carried out throughout the implementation process at both schools, and was complemented by quantitative (air pollution monitoring and leaf microscopy) and qualitative (interviews, surveys, and narratives) methods to achieve the various research aims. Air quality was only monitored at the Sheffield school, which showed that ‘thin’ green barriers (1.00-2.20 m) have the potential to reduce air pollution when properly designed and implemented. Air quality improvements were significant for the pollutant nitrogen dioxide (13%), but rather low for particulate matter (2%). Despite such small reductions, this research found that particulate matter is captured by the green barrier plants, and that this pollution reduction mechanism is maximised by plant biodiversity. Additionally, the Sheffield case study showed that a diligent green barrier design can provide other social (e.g., safety, wellbeing, and increased place quality), environmental (e.g., habitat provisioning for wildlife), and economic (increased subscription/interest in the school) benefits, which are highly valued by the school community. Finally, this research showed that the implementation of green barriers is largely influenced by its global context. Specifically, the Buenos Aires case study showed that green barrier implementation in a country without robust green intervention frameworks faces multiple obstacles, more than previously reported in the predominantly Euro-American literature. However, commitment, collaboration, and experimentation (as an urban living lab) can help overcome those hurdles. Overall, green barriers showed to be a valid complementary tool to the efforts of reducing and mitigating air pollution, with the relevant addition of creating safe and healthy environments for children and the broader school community