The November-2016 smog episode in Delhi, when air pollution had hit perilous levels, might have temporarily triggered a "spike" in the rate of death in the national capital, according to experts.
In the first week of November last year, Delhi's air quality had plunged, as the toxic smoke of the Diwali fireworks and the hostile weather conditions, trapped the pollutants, which in turn shrouded the city, severely affecting even visibility.
Anurag Agarwal, a scientist with the Delhi-based CSIR- Institute of Genomics and Integrative Biology, said the situation could very well have been like London's Great Smog of 1952, which had caused at least 4,000 deaths.
"There could have been a spike. During the London smog there was a big jump in the rate of death. But we don't have a system where we maintain a proper and full-proof record of deaths occurring in the city," he told PTI.
But how will one establish causality i.e. How will it be possible to link the temporary spike in death rate, if any, to rise in pollution levels?
Anumita Roychowdhury, head of Centre for Science and Environment's (CSE) air pollution lab, said causality has been established in cases of few other severe spells of smog, and even in India data is available which indicates towards the same.
"An AIIMS study has shown how during winters there is a rise in the number of hospitalisations of those suffering from cardiac and respiratory ailments. So we may not have data immediately about any such rise during last November but existing data clearly shows something similar could have occurred," she said.
Agarwal, who focuses on the biological and clinical aspects of respiratory diseases, explained how the London death figures were arrived at and said the same procedure can be applied here.
He said two sets of data: a) the actual death rate observed during the smog episode, and b) the death rate recorded during the corresponding period the previous year when pollution levels were low, would have to be factored in.
"You extrapolate the previous year's death rate as the baseline death rate. Then the actual death rate observed during the corresponding period will have to subtracted from the baseline rate. The result would be the excess death rate," he said.
Agarwal said his institute had thought about undertaking a similar exercise but later shelved it as not all deaths are recorded in Delhi at this point in the absence of a centralised digital register of medical records.
However, Mukesh Khare, professor of environmental engineering in IIT-Delhi, sounded sceptical about any relation between death rate and pollution level, saying the London episode cannot be compared to what Delhi experienced.
"This is primarily, because the meteorological conditions in the two cities vary widely. There may have been a spurt in respiratory diseases, but one cannot say the same about deaths," he said.
The November spell of smog was such that for the first time in history of the city, schools had to be shut, coal- based power plants were closed, as part of a raft of emergency measures declared by the Delhi government.
The Centre for Science and Environment (CSE) had described the situation as alarming and the smog episode as the worst in 17 years.