Kolkata: How much toxic air would you inhale travelling from the airport to New Garia in a cab? Or from Behala to Ballygunge? In the first case, the range is anything between 187 g to 548 g of particulate matter per cubic metre. Again, at Behala, a Kolkatan begins to consume 469 g. By the time he reaches Ballygunge, his consumption level shoots to 1,290 g.
Scary facts like these have been collated in a study conducted by the Centre for Science Environment (CSE) in January.
"Measuring exposure takes into account the health impact of particulate matter and other pollutants on commuters. It's when Kolkatans are on the road that they are at maximum risk," said Anumita Roy Chowdhury, head of the Delhi-based NGO's air pollution control campaign.
"Our exposure monitoring captures the level of pollution that people are exposed to due to closeness to different pollution sources in their immediate surroundings. This monitoring is different from the official ambient air quality monitoring that indicates the overall air quality of the city. Ambient concentrations do not always represent true human exposures," she added.
Referring to a health ministry study titled 'Steering committee on air pollution and health related Issues', which stresses on the importance of finding proximity to the source of pollution, Roy Chowdhury explained that what are we inhaling and how much time we spend near the pollution source is more important than what occurs generally in the air.
Focus on exposure can dramatically alter the conventional practice of ranking pollution sources based on their relative contribution to ambient concentration, according to experts. "Exposure-based ranking gives a clearer picture of the crisis. It not only re-orders the ranking of major outdoor emission sources but reveals an entirely different landscape of sources - those that may significantly affect exposure without appreciably affecting ambient concentration. Exposure to vehicular pollution is expected to be very high in Kolkata, which is one of the most densely populated cities in the world and where the majority lives or works near the roadside where levels are much higher," says Manas Ray, former assistant director and head research, Chittaranjan National Cancer Research Institute (CNCI). Studies by CNCI have found more than 60% children in Kolkata suffer from lung problems compared to 24% in cleaner surroundings.
Going a step further, the CSE study has found that on days when ambient data shows the average ambient PM2.5 levels in the range of 117 to 243 g per cubic metre, the actual exposure levels were 161 to 518 g per cubic metre, almost double the background ambient levels. The study finds modes of travelling like walking, open buses and autos have high level of exposure.
"This is very serious, because according to the Comprehensive Mobility Plan, around 70% of Kolkata's inhabitants suffer from respiratory problems such as asthma and lung cancer, caused by pollution from the city's chaotic transport sector," says Ray.
"Kolkata urgently needs a clean air action plan to reduce exposure to toxic vehicular fume by leapfrogging to Euro VI emissions standards, discouraging use of diesel, promote alternative fuels, enforce stringent inspection of emissions, penalize visibly smoky vehicles and regulate commercial vehicle movement," says green technologist SM Ghosh.
According to the University of California, Berkeley, the population-weighted intake fraction, or the grams of vehicle pollution inhaled per grams of vehicle pollution emitted in Kolkata, is four times higher than the world average - highest amongst all the key Indian metros.
