Officials at Met department said Delhi has been witnessing mist over past few days. They clarified that it is not smog and is likely to go away as the temperatures rise during the day.
A morning haze and deteriorating pollution levels in Delhi brought back memories of the smog that had engulfed the national capital in 2016.
Officials of the regional weather forecasting centre in Delhi, however, said that it is not smog, but just a mist that is being triggered over the past two to three days. They also said the mist is likely to go away as the day temperatures rise with the sun.
Mist and fog both occur when there are water droplets in the air. When warm water in the air cools quickly, the droplets change from invisible to visible.
Usually fog is a condition when visibility is less than 200 metre. That might not sound like much, but when it comes to morning driving, a visibility of around 50 metre could slowdown the vehicles triggering traffic snarls. If you can see farther than that, it’s considered mist.
“At the Safdarjung observatory the visibility at 8.30am was 2000 metre. Hence we can’t consider this as smog. It is just a mist. High humidity levels and a drop in the night temperature triggered the morning mist,” said a senior official of the local met department.
Usually on a clear sunny day and when pollution levels are very low, the visibility is more than five kilometres and above.
While easterly winds have helped the humidity levels to shoot up to around 80% over the past few days, the minimum temperature dropped to around 22 degrees Celsius.
What is aggravating the condition is the pollution level that has deteriorated from moderate to poor category over the past few days. However, the pollution level now is much lower than seen in 2016.
The Air Quality Index of Delhi which was less than 200 even on last Friday has shot up to 262 on Thursday morning.
“The primary pollutants are the particulate matter – PM2.5 and PM10. These are tiny droplets that are suspended in the air,” said D Saha head of the air quality laboratory at Central Pollution Control Board.
The website of System of Air Quality and Weather Forecasting and Research (SAFAR) under the Ministry of Earth Sciences revealed that levels of PM2.5 and PM10 are much above permissible limits and are likely to shoot up further in the next three days.