Medical scientists at the Centre for Research in Environmental Epidemiology in Barcelona have found that the greater the area under green spaces in a city, the greater the children's working memory and attentiveness in primary school classrooms.

The researchers point out that green spaces are known to mitigate traffic-related air pollution. "Part of the relationship we observed could be explained through the effect of green spaces on air pollution," said PayanDadvand, an assistant research professor at the Barcelona centre.

"In an earlier study, we had found that children from schools with higher levels of air pollution have slower cognitive development than those (from schools) with lower pollution levels," Dadvand told The Telegraph.

The study, published today in the journal Proceedings of the National Academy of Sciences, comes two weeks after India's environment minister Prakash Javadekar announced a plan to help municipalities increase tree cover in nearly 200 cities across the country.

Dadvand and his colleagues used satellite imagery and computer-based tests to explore the relationship between green spaces and cognitive development of children, adjusting their analyses for age, sex and socio-economic circumstances of schoolchildren in Barcelona.

They examined over 2,600 children with an average age of about eight-and-a-half years and found that greater green areas within and surrounding school boundaries was associated with greater working memory and reduced inattentiveness. Greenness on the way to school was also associated with better working memory, the researchers said. The ability of greenness within school boundaries to reduce air pollution could explain only a part of the observed association. Earlier laboratory and real world studies have found that green spaces can help reduce noise levels, stress and contribute to physical activity.

Lower levels of noise and stress and increased levels of physical activity could be indirect pathways that influence cognitive development, Dadvand said. "Green spaces provide children with opportunities for discovery, creativity, engagement and a sense of wonder, enhancing psychological restoration which could positively influence different aspects of cognitive development."

Javadekar had earlier this month announced a plan to launch an urban forestry scheme under which members of the public would be encouraged to plant trees on degraded land within the municipal localities of nearly 200 towns across the country. #In Pune, the first city where the scheme will start, municipal authorities have identified a 70-hectare patch of degraded forest land where about 4000 trees are expected to be planted in the coming weeks.

The environment ministry has sought information about the availability of degraded land within these towns from their municipal authorities. Environmental scientists say urban forests can help reduce air and noise pollution, absorb carbon dioxide, and alter the local microclimate.

The current urban forest space in India varies across cities. According to 2011 estimates, about 78sqkm of south Delhi's geographical area of 250sqkm is forest, while Calcutta and Howrah have 157sqkm forest within their combined area of 1,467sqkm. Only 2sqkm of Mumbai's 157sqkm is forest.