Fog episodes in Indo-Gangetic Plains more intense and frequent: World Met body

The Indo-Gangetic Plain (IGP), home to over 900 million people, has experienced a marked rise in air pollution as well as winter fog episodes, the World Meteorological Organization (WMO) said on Friday.

Although fog is a seasonal occurrence, the WMO said its growing frequency and duration are increasingly linked to ever-increasing human activities and regional environmental changes.

Fog forms when air near the ground cools to the dew point, allowing moisture to condense on certain airborne particles [known as 'fog condensation nuclei' (FCN)] and form tiny droplets. This process is heavily influenced by fine particles (PM2.5) in the atmosphere, released from sources like tail-pipe emission, industrial flue gas and burning of crop residue, fossil fuel and domestic biomass.

These FCN cause more persistent and dense fog formation.

During winter, temperature inversions, where cold air becomes trapped beneath a layer of warmer air, lock pollutants near the ground, thereby extending the duration of fog events, the WMO said in its latest air quality and climate bulletin.

It said that mushrooming of urban areas within the IGP has led to enhanced emissions and to the development of urban heat islands, altering local weather dynamics.

Sources of emissions include vehicles and construction. Another source is ammonium emitted from large cattle populations and poor sanitation facilities. When this ammonium interacts with other chemicals in the atmosphere, stable FCNs are formed. This, in turn, results in persistent fog, the WMO's bulletin said.

The UN weather and climate agency said that many brick kilns, using inferior coal and obsolete technology, further increase organic aerosol emissions.

One dominant seasonal contributor to emissions is the burning of post-monsoon agricultural residue, particularly in Punjab and Haryana.

Satellite data confirm sharp increases in aerosol optical depth during these months, correlating with spikes in fog intensity all along the IGP, it said.

The interaction of fog droplets with aerosols also alters aerosol chemistry, with consequences for both climate and pollution.

Poor visibility during fog episodes impacts transportation, causing delays and accidents.

Fog also causes severe health conditions such as asthma, bronchitis and other respiratory ailments. Elevated levels of toxic metals and organic compounds in fog water are a public health concern, the WMO said.