AQI turns ‘very poor’ as temperature dips, doctors raise health alarm

Kolkata: The air quality of the city has worsened with a dip in temperature and a drop in wind velocity. All monitoring stations, except Fort William and Rabindra Sarobar, showed red or very poor (AQI: 301-400) air that has triggered a spike in respiratory ailments.

The commonest manifestation of the impact of poor air quality is a persistent cough, said health experts.

Salt Lake and Jadavpur showed the worst air quality. Salt Lake showed an extraordinary spike above 340 throughout the day. Fort William and Rabindra Sarobar showed the best possible air quality, a notch below the city’s average air quality – poor (201-300). Long-term exposure to the ambient air of these two places can make one sick, experts said.

“Viral fever and cough usually don’t last for more than a week. But the spurt in pollution has helped in the spread of the viruses,” said Sanjukta Dutta, head of emergency medicine, Fortis Hospital. Currently, the AQI is driven by finer particulate matter PM 2.5.

The PM 2.5 particle is about 3 per cent of the diameter of a human hair and can travel straight into the bloodstream. The noxious chemicals ride piggyback on these particles.

“Since thermal inversion is at play, vertical wind movement has significantly reduced due to lower radiative temperature at the ground. This phenomenon occurs when the soil is cool and there is no transfer of heat from the soil. It causes calm wind conditions in the lower atmosphere.

The pollutants tend to hang low in the atmosphere at the breathable height of people,” explained a PCB scientist. In winter, the emission of the second day piles up on the pollutants of the first day as the air finds no time to heal itself with pollutants circulating in the lower atmosphere.

The meteorology has a major role to play. Kolkata being at the tail end of the Indo-Gangetic Plain (IGP) is always at the receiving end of massive transboundary pollution from north India, necessitating an air-shed-based mitigating approach rather than a city-based approach, said a senior PCB official.

With the worsening of AQI, health experts raised alarm against long-term exposure to such filthy air. “People must avoid morning walks when the AQI is at its peak. N95 masks, which prevent finer particulate matter from travelling into the nasal tract, is mandatory outside.

PM2.5 is responsible for the high rate of premature mortality in Kolkata and other Indian cities,” said Arup Halder, a pulmonologist with Woodlands Hospital.