NEW DELHI: Delhi's not the only culprit. A recent study by Indian Institute of Technology, Delhi, has found that the city's emissions, though considerable, are not alone responsible for the sudden peaks in particulate matter (PM 10) levels in it. Far-off sources in north India or even beyond India (within Asia) may be contributing as much as 24% of PM 10. And on days when PM 10 concentration is very high here, only about 11% of it may have been contributed by polluting sources within Delhi.
The study, published online in the Atmospheric Research Pollution journal, has used a chemical transport model to interpret Delhi's PM 10 levels from June 2010 values to assess how much of it was caused due to emissions within the capital. The data was mapped on four geopolitical domains—Asia, India, north India and Delhi.
The team found that contribution from sources in Delhi alone was about 11% to 41% and a major proportion (59% to 89%) was from sources outside Delhi. While this may seem like a wide range, it was found that, on days when PM 10 concentrations were low in Delhi, the contribution from sources within Delhi was higher (41.5%). But on days when PM 10 concentration was very high (over 500 micrograms per cubic metre), the contribution from Delhi was only about 11%, from north India and surrounding areas about 69.2%, and from outside India about 19.6%.
The study, however, doesn't focus on specific areas outside Delhi affecting its air quality. "We will assess the sources in another study. These are likely to be areas with large thermal power plants and big polluting industries," says Manju Mohan, professor at Centre for Atmospheric Sciences, IIT Delhi, who co-authored the study with PhD scholar Medhavi Gupta.
"Sudden peaks in PM 10 levels cannot be due to domestic sources. The peaks are a result of pollutants traveling from a long distance. It may take up to a couple of days for polluting particles from outside to reach Delhi," adds Mohan.
Experts say the findings indicate that we need strict pollution norms for the entire region. "Delhi is already contributing to a huge amount of air pollution which needs to be mitigated. Along with that, we need similar strict norms for all cities and towns. That is why we are talking of an air pollution action plan for NCR and not just for Delhi. Even towns like Meerut should have the same norms," says Anumita Roy, Executive Director-Research and Advocacy, Centre for Science and Environment.
