Today we would try to understand the meteorological conditions which are responsible for making our air murky during winter. There could be many reasons behind it. The most important is a temperature inversion. In a temperature inversion, the air warm air lies above the cold air. The condition happens during the winter. In winter at night the earth cools down faster than the air above it, leaving the cold air below the warm air. Such a condition is termed temperature inversion. The temperature inversion makes the atmosphere stable. Though the stability is conditional only, which means the atmosphere will be stable as long as the temperature inversion exists. In a stable atmosphere, the vertical mixing of the pollutants is stopped. So the pollutants remain trapped in the ground layer of the atmosphere, which causes serious health hazards. Furthermore, the horizontal movement of air is low at the ground surface which would result in the slow dilution of the pollutants into the atmosphere. Both these conditions sum up to aggravate the pollution problem during winter. This is the reason that people suffering from respiratory disorders are having hard times during winter.
Usually, fog is associated with inversion, as the temperature is below the dew point of water vapour. This is the reason for poor visibility during the winter. The relative humidity is the precursor for the development of fog and corrosion of the metal surface. The sun’s rays during these winters would lead the episodes of photochemical smog which is a serious health hazard. The sun’s rays also help in the generation of ground ozone, which is commonly called bad ozone. It is having harmful effects on plants, animals and the environment.
The unstable atmosphere encourages the upward movement of air pollutants. The air pollutants move upwards and as they move upwards they are drifted to different regions by the fast-moving winds which usually occur at a height of around 200 to 300 m. The unstable atmosphere takes away the pollutants from the breathing zone of humans, thus preventing humans from different respiratory disorders. Further, the dilution helps in making the air cleaner comparatively. The wind is also an important factor that helps in the dilution of pollutants. The wind takes away the pollutants rapidly from the source and hence prevents exposure to higher concentrations of pollutants. The greater the height of the chimneys, the greater the chances of pollutant dilution due to convective currents. The lower height of the chimneys adds to the woes of air pollution.
The surface winds cause different types of eddies due to changes in climatic conditions and the topography of the area. These winds having varying speeds and directions are called turbulence. The turbulence causes the instability of the atmosphere which helps in the vertical movement of the pollutants, thus resulting in the dilution of the pollutants in the atmosphere. Rains help in improving the air quality. The wet deposition of the pollutants occurs due to rain. The rain brings down the particulate matter and gases soluble in water to the surface, hence making the air clean of pollutants.

Manzoor Ahmad Bhat is Faculty EVS, Sankoo campus, GDC Kargil. Feedback at [email protected]

Manzoor Bhat