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Delhi air alert for next three days

A cyclist covers his face in Delhi on Tuesday. (AFP)

New Delhi: Air pollution levels over the National Capital Region, labelled "poor" on Tuesday, could deteriorate into the "very poor" category over the next three days depending on weather conditions, a senior meteorologist tracking air quality said.

Gufran Beig, deputy director at the Indian Institute of Tropical Meteorology, Pune, said falling temperatures in northern India and an observed increase in humidity through moisture incursion portended a worsening of the air quality from Wednesday to Friday unless rain washed off the pollutants.

The Union earth science ministry's network of stations monitoring air quality predicted that concentrations of tiny particulate matter sized 2.5 microns (PM2.5) would increase over Delhi from 206 micrograms per cubic metre on Tuesday to 216 on Wednesday and 226 after three days.

"The weather is an important factor that influences the concentrations of pollutants - and weather conditions over the capital are now conducive for a deterioration of air quality over the next three days," Beig told The Telegraph.

The network also predicted that the concentrations of particles sized 10 microns (PM10) would increase from 339 on Tuesday to 356 on Wednesday and to 373 after three days.

Both sets of predicted values are three times higher than the prescribed limits of 60 for PM2.5 and 100 for PM10.

The falling temperatures associated with the onset of winter shrink the volume of air in which air pollutants are trapped, which translates into higher density of pollutants.

Westerly winds blowing over the capital have also brought in moisture that raises humidity, which increases the "holding capacity" of the atmosphere and elevate the concentrations of pollutants, he said.

The India Meteorological Department has predicted a "cloudy sky with light rain or drizzle". Beig said under the current weather conditions, a drizzle or light rain was unlikely to help clear the air. "Heavy rain or strong winds can quickly dissipate pollutants," he said.

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