The Indira Gandhi International Airport in Delhi recorded the worst levels of smog in 17 years on November 2, with visibility as low as 300-400 metres (m). The period between 11AM and 2:30PM was the worst in the day with respect to airport visibility.

The post-Diwali smog reduced the visibility there to 800-1200 m since October 30. Pollution during Diwali along with other weather-related factors is being cited as the reason for abnormal smog level.

Data for the month of November in the years 2000-2016 was studied to analyse visibility and smog levels at the airport. In 2012, the visibility at the airport had fallen to 700-800 m on November 2, when a prolonged smog coverage spell took over the airport from October 28 to November 8.

Causes of excessive smog

Apart from air pollution during Diwali, weather-related factors have contributed to the worsening of visibility. Full establishment lower level anticyclone—a weather phenomenon which prevented the dispersion of smog— developed around Delhi on November 2.  The surface stable boundary layer has strengthened to 600 m in height, as against its 300 m in the previous two days. Light or no wind presence in the vertical column has also added to the problem.

What is the forecast?

As per the forecast from different models, gradual improvement of the smog-related low visibility is expected in the coming days. Visibility may touch  around 500-1200 m on November 3 and 4. However, major improvement is predicted only after November 6-7, with the onset of 10-15kmph winds.

Early morning fog will continue to develop in the coming days. Forecast predicts building up of fog during morning 5AM to 9AM with visibility touching 200-300 m. Fog will intensify  on the morning of November 3, reducing visibility to 100m during early hours.

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