Orange alert for fog; road, rail, air traftic to be affected

The India Meteorological Department (IMD) has issued an orange alert for "dense" to "very dense" fog in Delhi on Monday, predicting that visibility may drop to as low as 200m in most of the Capital and the surrounding region, affecting road, rail, and air traffic.

"There are chances of dense to very dense fog in Delhi on Monday. An orange alert has thus been issued, with smog expected later in the day too," said an IMD official.

IMD defines "shallow" fog in a region when visibility drops to 500-1,000m, "moderate" fog when visibility is 200-500m, "dense" fog when visibility is 50-200m, and "very dense" when visibility dips to 50m or lower.

If visibility is less than 1,000 metres and relative humidity is more than 75%, it is termed as fog. If the relative humidity is less than 75%, it is called smog.