The India Meteorological Department has issued a warning for “dense to very dense fog” over the next three days in parts of Punjab, Haryana, Chandigarh, Delhi and West Uttar Pradesh.

Dense fog was reported from many places in Punjab, Haryana, Delhi and parts of Uttar Pradesh and north Madhya Pradesh with visibility (50 m or less) recorded at many places, including Amritsar, Ambala, Delhi, Agra, Gwalior and Jhansi.

But the situation is expected to improve around January 21 when Punjab, Haryana, Delhi, Chandigarh, West Uttar Pradesh and Central India receive rain and thunderstorm due to an interaction between an incoming western disturbance and an easterly wave.

Meteorologists expect rain and accompanying winds will “mix the height of pollution”, which is currently close to the ground and reduce pollution levels in the region, thereby improving the situation.

The western disturbance will affect the western Himalayan region from the night of January 20, causing moderate to heavy snowfall over the region.

Fog is a normal occurrence in the plains from October onwards. But some studies on data tracked from 1970 onward show its frequency, duration and intensity has been increasing across north India. The biggest culprit is pollution — automobile, industrial and agricultural alike. Four conditions are crucial to the fog build-up — low temperature, moisture, no winds and clear sky.

But pollution from transport and industrial sectors — the suspended particulate matter, a major urban pollutant — has been found to have a direct correlation with triggering and further intensifying fog. Power plant pollution further adds to it.

So while on one side, air pollution intensifies fog, throwing the normal life out of gear, it also happens to be the single biggest cause of environmental health risks.

Environmentalist Anumita Roy Chowdhury says pollution is affecting the air quality of cities of India. “Levels have increased over the time.

Along with the city-based pollution, there is also the pollution outside the city limits. In states such as Haryana and Punjab, agricultural and industrial pollution contribute along with the heavy-duty vehicular traffic”.

“Overall massage is clear. Cities will have to reduce dependence on personal vehicles, control motorisation, curtail use of use diesel vehicles and scale up the public transport. Along with it, all cities should be able to develop air pollution monitoring system so that they can inform the people about it on a daily basis and implement controlling measures,” she adds.

Clearly lot of weather changes are also happening. Recent data by US’ National Aeronautics and Space Administration (NASA) and National Oceanic and Atmospheric Association (NOAA) confirmed last year as the hottest 12 months since record-keeping began in 1880