An 11-month-long mobile monitoring of various particulate air pollutants over a fixed 150-km road stretch in the city, comprising major, arterial and residential roads, found large spatial variability along the study route for all pollutant concentrations. While urban and peri-urban residential neighbourhoods recorded the lowest PM2.5, BC (black carbon) and UPF (ultrafine particles) concentration, major roads recorded the highest concentration. Within the neighbourhoods surveyed, concentrations varied with the road type.
The study was conducted by the Centre for Study of Science, Technology and Policy (CSTEP) with ILK Labs, University of Washington and University of Texas. It is said to be one of the first large-scale mobile-monitoring studies in India comprising over a million data points. The report, titled ‘Mobile-Monitoring Campaign for Air Pollution Studies in Bengaluru’, stated that the research team completed a total of 27 repeat measurements over the study route to construct a long-term mean pollution map. The study route was divided into four parts, and each part was covered in one measurement day, which spanned almost four hours, from about 9 a.m. to 1 p.m., capturing the rush-hour peak.
On-road measurement of air pollutants – BC, PM2.5 and UFPs – were performed in four parts of Bengaluru. The mobile-monitoring route included the central business district (CBD), a residential urban neighbourhood (Malleswaram), a peri-urban neighbourhood (Kannuru), and an urban-rural transect.
“Kannuru is a peri-urban location used by Bruhat Bengaluru Mahanagara Palike (BBMP) for land filling. It is approximately 18 km from the CBD and characterised by less traffic. The area has a quarry due to which heavy-duty trucks ply here. The CBD includes M.G. Road and major roads around Cubbon Park and Vidhan Soudha. The study route reflects variations in the traffic volume, traffic density, driving speeds, and street configurations,” stated the report.
Sreekanth Vakacherla from CSTEP, one of the contributors to the study, said that they also covered all seasons to understand on-road pollution. The monitoring campaign started in May 2019 and continued up to the first week of March 2020. There were around 110 measurement days covering all seasons.
“By studying on-road pollution, we wanted to measure pollution levels that the commuter will get exposed to as we are moving closer to the source of pollution and components such as BC are detrimental to health,” he said. Their monitoring platform was a car fuelled by CNG (compressed natural gas), which is low-emitting but not completely emission-free.
Researchers found that each pollutant peaked in different regions along the study route. “Irrespective of the road classification and season, on-road PM2.5 levels were higher than ambient,” the report said. In Bengaluru, garbage/waste burning also contributes to observed on-road BC, in addition to diesel emissions.
Advocating for mobile monitoring in the country, the researchers said, “Air-quality monitoring forms a critical component of various stages of air-quality management. India has nearly 200 monitoring stations (operational during 2010-16). However, the country needs about 40,003 stationary monitors to capture the spatial and temporal variability of air quality,” it said.
“One way of avoiding pollution would be to avoid such roads. But it may not be feasible. We tried to see how many hospitals and schools are there along such roads, and there are many and they house more vulnerable people. In the future, it is advisable for them to not be located on such roads,” Dr. Sreekanth added.
The city centre is not a pollution hotspot in the case of Bengaluru. In addition to some of the busiest commercial areas, the CBD encompasses large green spaces such as Cubbon Park.
The hotspot areas are not the same for all pollutants. PM2.5 peaks (reaching ~60 µg m-3) 10–12 km from the city centre while BC peaks (reaching ~75 µg m-3) 7–9 km away from the city centre.
A clear peak was not seen in UFPs, but values remained high (reaching ~1,50,000 cm-3) till 7 km away from the city centre.
Within the residential neighbourhood, arterial roads connecting to the major roads were characterised by relatively higher PM2.5 levels. Major roads (highways/Outer Ring Road) displayed the highest levels of pollution.
BC and UFPs had the lowest values over residential neighbourhoods (urban and peri-urban), followed by arterial and major roads.