How air pollution helps urban Delhi stay cooler during the day

A man wears face protection against air pollution while riding on  a bicycle in New Delhi.

Neighbourhood News Desk: Strange it may sound but air pollution, along with many other factors, helps to keep Delhi cooler by at least two to four degrees than the surrounding rural areas during peak summer, researchers have found. This cooling effect, which scientists call the ‘urban cool island’, is experienced at least two times a year — first in May-June during peak summer and again between October and December in winter.This phenomenon is the opposite of the ‘urban heat island’ in which cities tend to be warmer because of the trapped heat.

Scientists said aerosol pollution, which increases during these two periods. Aerosols are minute particles suspended in the atmosphere and comprise almost anything from road dust, sea salt, desert sand, sulphates, nitrates, mineral dust and even moisture among others. Some experts said that the cool effect remains only for two to three hours after sunrise. As the day progresses and the heat increases, more convection currents in the air led to deepening of the atmospheric boundary layer. This causes the particles to disperse and the urban-rural difference fades.

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