As Kosaku mentioned on his blog, air quality in the built environment continues to be a primary health concern as the majority (i.e., 54% in 2014) of the world’s population currently lives in urban areas, and this is projected to rise to 66% by 2050 (United Nations, 2014). In accordance with the research findings of Kumar et al. in 2016, air pollution in urban areas is mainly caused by traffic emissions. Therefore, to create a better lifestyle in cities, hedges, trees and other green infrastructure should be considered and included in future urban planning.
Green infrastructure of a built environment is seen as a potential solution on urban planning, which can improve air quality, enhance urban sustainability, and enlarge the population there (Salmond et al., 2016). Trees on the streets and roads, hedgerows, green walls and green roofs are included in the green solutions (Fantozzi et al., 2015). As porous bodies, they can affect the local diffusion of pollutants, depose and remove air pollutants, and make the air cleaner.
Every coin has two sides and there is no exception for the green infrastructure. Because of its location in the city and its vegetation properties, green infrastructure also has both good and bad impacts on the air quality of streets (Kumar, 2017).
In an environment of “canyon street” with densely built skyscrapers on both sides, trees and other high green infrastructure are generally inconducive to air quality and hedges and other low-level green infrastructure help to improve the air quality there. Similarly, green roofs and walls can play the role of a sink, and reduce the exposed air pollution (Kumar et al., 2011).
In open roads and streets, if the vegetation barriers are tall and thick and close to each other, new vehicle emission of a high concentration cannot arrive at the roadsides along which people may live nearby, take a walk or go cycling (Morakinyo and Lam, 2016).
Except reducing air pollution, green infrastructure in urban areas also has benefits in other aspects such as mitigating climate change, reducing energy consumption, mitigating heat island and managing floods better (Gallagher et al., 2015).
Fantozzi, F., Monaci, F., Blanusa, T., Bargagli, R., (2015). “Spatio-temporal variations of ozone and nitrogen dioxide concentrations under urban trees and in a nearby open area”. Urban Climate. Vol. 12, pp.119-127.
Kumar, P., Abhijith, K.V., Gallagher, J., McNabola, A., Baldauf, R., Pilla,F., Broderick, B., Sabatino, S. D., Pulvirenti, B. (2017). “Air pollution abatement performances of green infrastructure in open road and built-up street canyon environments A review”. Atmospheric Environment. Vol. 162, pp.71-86.
Kumar, P., Fatima Andrade, M., Ynoue, R.Y., Fornaro, A., de Freitas, E.D., Martins, J., Martins, L.D., Albuquerque, T., Zhang, Y., Morawska, L., (2016). “New directions: from biofuels to wood stoves: the modern and ancient air quality challenges in the megacity of Sau Paulo”. Atmospheric Environment. Vol. 140, pp.364-369.
Kumar, P., Ketzel, M., Vardoulakis, S., Pirjola, L., Britter, R., (2011). “Dynamics and dispersion modelling of nanoparticles from road traffic in the urban atmospheric environment-A review”. Journal of Aerosol Science. Vol. 42(9), pp.580-603.
Salmond, J.A., Tadaki, M., Vardoulakis, S., Arbuthnott, K., Coutts, A., Demuzere, M., Dirks, K.N., Heaviside, C., Lim, S., Macintyre, H., McInnes, R.N., Wheeler, B.W., (2016). “Health and climate related ecosystem services provided by street trees in the urban environment”. Environmental Health. Vol. 15, p.36.
United Nations, (2014). World urbanization prospects 2014. Demogr. Res. 32.