Lack of access to green spaces coupled with long-term exposure to air pollution increases the risk of hospitalisation for respiratory disorders, medical researchers have said in a study, adding fresh evidence for the gifts of greenery.

Multiple studies in the past have established how air pollution increases the risk of respiratory disorders such as asthma or chronic obstructive pulmonary disease (COPD) that can be compensated by access to tree-lined parks or gardens. But data on their impacts on hospitalisation has been scanty.

The new study to be presented on Sunday at the European Research Society’s conference in Vienna, Austria, has found a 30 to 45 per cent increased risk of hospitalisation with each interquartile range increase in pollutants such as soot and nitrogen dioxide. Proximity to greenery lowered the risk.

“Air pollution contributes to persistent inflammation and oxidative stress in the respiratory system,” said Shanshan Xu, a researcher at the department of global public health and primary care, University of Bergen, Norway. “These harmful processes can lead to the development and exacerbation of chronic respiratory diseases which can escalate into severe health episodes requiring hospital care.”

Xu and her team members tracked the health of 1,644 people from five countries, analysing their potential exposure between 1990 and 2000 to particulate matter, black carbon, nitrogen dioxide, and ozone as well as the level of green landscapes around their homes.

Although greenery was associated with a decreased risk of respiratory hospitalisation, it also led to increased number of respiratory emergency room visits which the researchers have attributed to the co-presence of hay fever, an allergic condition.

Their findings come alongside independent research by an international team of scientists indicating cities in low- and middle-income countries on average have just 70 per cent of the “cooling capacity” provided by the urban greenery in cities in high-
income countries.

The relatively lower greenery in low- and middle-income countries, environmental health researchers say, is a cause of worry not just for exacerbation of respiratory disorders but also for extreme heat.

Amid rising global temperatures, a phenomenon called the urban heat island effect can make cities effectively hotter than rural areas, and lack of greenery can raise temperatures even within localities.

“Our analysis suggests that green spaces can cool the surface temperature in the average city by about 3°C during warm seasons — a vital difference during extreme heat,” said Tim Lenton, the chair of climate change at the University Exeter in the UK who led the research on green spaces worldwide.

A study led by researchers at the Barcelona Institute of Global Health four years ago had found that a rapid increase in built-up land use — meaning absence of greenery — within 300 metres of a person’s residence was associated with an increase in risk for high blood pressure, obesity, and diabetes.