Building green and blue spaces, such as parks, in new communities is crucial for cleaner air

Surrey's Global Centre for Clean Air Research (GCARE), working with 30 co-authors from seven countries, found that parks may be the most effective solution for reducing overall air pollution -- cutting air pollution by 22% city-wide. However, the study highlights the importance of evaluating how well different types of green, blue, and grey infrastructure (GBGI) work in smaller spaces and recognising that parks can include multiple features, which together enhance their impact.

The study also examined other common types of green, blue, and grey infrastructure (GBGI), such as trees, green walls, and hedges, and found mixed results for their ability to reduce air pollution.

Trees were most effective in open-road conditions, where they could cut pollution by up to 77%. However, the researchers discovered that planting trees in narrow, enclosed streets -- known as street canyons -can sometimes worsen air quality. This is because certain tree species and arrangements can block airflow, trapping pollution.

Professor Prashant Kumar, lead author of the study and Founding Director of GCARE at the University of Surrey, and the Director of the RECLAIM, said:

"We are beginning to understand just how powerful green infrastructure can be against urban air pollution, but their effectiveness hinges on where and how they are implemented. Our review has found that well-placed greenery can cut black carbon levels by up to 40%, making our communities greener and healthier."

The research is part of the RECLAIM (Reclaiming Forgotten Cities -- Turning Cities from Vulnerable Spaces to Healthy Places for People) project. RECLAIM is a £1.45m UK Research and Innovation-funded Network Plus initiative. It is led by GCARE in collaboration with the UK Centre for Ecology & Hydrology and the Universities of Bath, Bangor and Warwick.

According to the World Health Organization, ambient (outdoor) air pollution caused 4.2 million deaths in 2019. Major sources of outdoor air pollution include vehicles, power generation, and residential energy for cooking and heating.

Professor Kumar added:

"We have discovered that many of the GBGI lack scientific evidence regarding their effectiveness in removing air pollution. Decisions are often based on expert judgments, and so it is crucial that we fill this knowledge gap as quickly as possible for informed decision-making and for maximising the potential of GBGI."