Unseasonal rain brings down Delhi's pollution

The unseasonal wet spell, while giving the people of Delhi a respite from the heat, had another bonus - bringing down pollution levels in the city ranked the world's worst polluted by the WHO.

A comparative analysis of the real-time ambient air quality data of the Delhi Pollution Control Committee showed a significant drop in the level of pollution.

Online data recorded a level even lower than 60 microgramme/cubic metre (mcg/cu.m, which is the ambient air quality standard for PM2.5 set by the Central Pollution Control Board for dust, dirt, soot, smoke, and liquid droplets particles less than 10 micrometers in diameter (PM10) which pose a health concern because they can be inhaled and accumulate in the respiratory system.

The WHO norm, however, is 25 mcg/cu.m.

Centre for Science and Environment programme manager Vivek Chhattopadhyay said the rainy season records best pollution levels while the winter and the summer seasons are the worst.

"Rains will definitely bring the pollution level down as pollution is the lowest during rainy season. The PM level reduces because dust particles are soluble in rain drops," Chhattopadhyay told IANS.

The busy neighbourhood of R.K Puram in south Delhi, for instance, registered the highest level at 38 mcg/cu.m during the three days the data was recorded between March 29 and April 4. It was the week Delhi received untimely showers.

This is in sharp contrast with the levels during March 22-28 that were over four times higher than even the standard, with highest touching 280 mcg/cu.m and the lowest settling at 80 mcg/cu.m.

However, Chhattopadhyay was quick to caution that the "good news" wouldn't last for long because "the dust particles will rise up again when the rain stops".

"The question is whether we depend on rain or check the problem of pollution all year long," he said, and called for checking the scourge of pollution instead of depending on rain as solution.