The overall levels of annual average PM2.5 also rose in this period, according to data from a new air pollution model developed by Indian and international researchers. PM2.5 refers to tiny particles of matter that can easily slip inside the lungs. By 2018, the minimum levels of annual average PM2.5 were touching 40ug/m3-eight times the WHO guideline.
Track the pollution level in your city
Even in the lockdown periods during Covid, the base levels of PM2.5 didn’t come down much, said Siddhartha Mandal, an environmental epidemiologist with the Public Health Foundation of India, which led the research. The spatial analysis shows a distinct northward shift of high PM2.5 levels from the south to central parts of the island city and further to the eastern and western suburbs. Already polluted eastern areas like Chembur and M ward seem to have worsened over this period.
These trends “align with what we are seeing,” said Ronak Sutaria, founder of Respirer Living Sciences, who is not associated with the study. “It’s confirming certain spatial trends.”
The data also shows that each year can look very different, even if overall trends are rising. For instance, the model finds lower pollution levels in 2019-the year before the pandemic lockdown-for no clear reason. But these annual fluctuations are not huge, Mandal said, and likely influenced by weather.
The analysis uses a national exposure model developed by the Consortium for Climate Health and Air Pollution Research in India (CHAIR) to fill the gaps in air pollution data. Using this model, researchers can go back and link pollution exposure to health data to look for associations, said Mandal.
This is not a city-specific model, but a national model, Mandal noted, and is expected to be especially useful for rural areas and small towns where air pollution monitoring is sparse to non-existent. But even in cities with more monitors, Mandal says there’s scope for using this model to analyse specific hotspot areas over time or correlate with illnesses like tuberculosis in the area.
In the absence of a dense and hyperlocal network of monitoring stations, this kind of research is “sorely needed” to fill in gaps in understanding pollution trends in the city, Sutaria said. London has 650 air monitoring sites, he noted, compared with Mumbai’s 20-odd stations. “A city like Mumbai needs much more granular data.”