Asthma Attacks Reduced in Tree-Lined Urban Neighborhoods

People living in polluted urban areas are far less likely to be admitted to hospital with asthma when there are lots of trees in their neighborhood.

Urban greenery. Image credit: Fgrammen/Wikipedia (CC BY-SA 3.0)

The study conducted by the University of Exeter's medical school into the impact of urban greenery on asthma suggests that respiratory health can be improved by the expansion of tree cover in very polluted urban neighbourhoods.

In the most polluted urban areas, trees had a particularly strong association with fewer emergency asthma cases. In relatively unpolluted urban neighbourhoods trees did not have the same impact.

In a typical urban area with a high level of background air pollution -- for example, around 15 micrograms of fine particulate matter (PM2.5) per cubic metre, or a nitrogen dioxide concentration around 33 micrograms per cubic metre -- an extra 300 trees per square kilometre was associated with around 50 fewer emergency asthma cases per 100,000 residents over the 15 year study period.

Greenspace and gardens were associated with reductions in asthma hospitalisation at lower pollutant levels, but not in the most polluted urban areas. With trees it was the other way round. It may be that grass pollens become more allergenic when combined with air pollutants so that the benefits of greenspace diminish as pollution increases.

In contrast, trees can effectively remove pollutants from the air, and this may explain why they appear to be most beneficial where concentrations are high.

The findings could have important implications for planning and public health policy, and suggest that tree planting could play a role in reducing the effects of air pollution from cars. (Tasnim News Agency)

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