Vanishing canopies affect air quality

Not only pollution levels but also pattern of planting trees has undergone a change

In a survey conducted at ten major road junctions in Bangalore (tree lanes and treeless lanes) by a City-based environment group, it was found that pollutants around canopy trees were comparatively less than along treeless stretch.
The study conducted by ATREE (Ashoka Trust for Research in Ecology and the Environment) in collaboration with Environmental Sciences Departments of St Joseph’s College and Mount Carmel College has found huge differences in air quality.
Dr Harini Nagendra, Urban Ecology Program Coordinator at ATREE, who supervised the study, said that it is not just pollution levels but also the planting patterns that have changed in the recent times.  “Trees with huge canopies planted by our forefathers have been replaced with smaller trees by BBMP,” she said.

The BBMP’s Tree officer M R Suresh corroborated that species like Gulmohar, Rain trees and Spathodia will not be planted henceforth. “Gulmohar trees have very loose roots and are uprooted easily. Rain trees and Sapthodia are gigantic trees and there is absolutely no place for such trees in the City now,” he said.
He added that only smaller canopy trees will be planted henceforth.
The study looked at air pollution, temperature and humidity at two nearby areas with streets lined with trees and areas without trees. Air pollution levels were studied using a high volume air sampler that estimated the levels of Suspended Particulate Matter (SPM) and SO2. Dr Harini pointed out that street trees significantly reduced the levels of SO2 and SPM, reduced temperature, and increased humidity.

One significant point was that the levels of SO2 in most locations (with and without trees) were lower than the National Ambient Air Quality (NAAQ) Standards (anything above 60 micrograms/cubic meter is considered hazardous).
“The SPM levels for most locations without trees were much higher than the NAAQ specified standards (200 micrograms/cubic meter) but the levels came down to permissible levels when there are street trees,” said Dr Harini.
The study was conducted at Jeevan Bhima Nagar, Race Course Road, Magadi Road, NGEF Main Road, Basavanagudi Ring Road, Sarjapur Road, Banashankari Ring Road, Lalbagh Road and Mekhri Circle junction and Bannerghatta Road by field research team Lionel Sujay Vailshery, Madhumitha J, Suparsh Nagendran and Richa Chowdhury in August and September.