The National Capital Region is going through this year’s worst spell of air pollution, forcing the Delhi government and central authorities to announce a slew of emergency measures to minimise health hazards.
NCR is covered with dense layer of smog and it’s advised to remain indoor. Most forms of condensation in the atmosphere result from the air being cooled in some way or the other. Condensation near the ground results from contact cooling, advection cooling and radiation cooling. Let’s explain the difference between mist, fog, smog, haze and vog.
Mist is a phenomenon caused by small droplets of water suspended in air. Physically, it is an example of a dispersion. It is most commonly seen where warm, moist air meets sudden cooling, such as in exhaled air in the winter. Mist also forms on wet surfaces, lakes or rivers, where the humidity is high and condensation in evening has led to wisps of mist over the fields and near water.
Fog consists of visible cloud water droplets or ice crystals suspended in the air at or near the Earth's surface. Fog can be considered a type of low-lying cloud and is heavily influenced by nearby bodies of water, topography, and wind conditions. A mist becomes a fog when the visibility is reduced to below one kilometre (1000mts). Fogs are formed due to different causes and so, there are different types of fog , one produced by cooling and the other by evaporation.
As originally coined in 1905 by Des Voeux, a natural fog contaminated by industrial pollutants, a mixture of smoke and fog. Today, it is the common term applied to problematical, largely urban, air pollution with or without the “natural fog”. Smog is produced as automobile exhausts build up when weather condtitions produce stagnant air masses that do not allow exhausts to disburse.
This kind of visible air pollution is composed of nitrogen oxides, sulphur oxides, ozone, smoke or particulates among others (carbon monoxide, CFCs and radioactive sources). Human-made smog is derived from coal emissions, vehicular emissions, industrial emissions, forest and agricultural fires and photochemical reactions of these emissions. In Delhi, smog severity is often aggravated by stubble burning in neighboring agricultural areas. It is usually highly toxic to humans and can cause severe sickness, shortened life or death.
Haze is an atmospheric obscurity due to minute suspended solid matter, such as dust or smoke particles, in the sky. The particles are too small to be seen or felt individually, but they diminish visibility. Sources for haze particles include farming (ploughing in dry weather), traffic, industry, and wildfires.
Vog is a form of air pollution that results when sulfur dioxide and other gases and particles emitted by an erupting volcano react with oxygen and moisture in the presence of sunlight. The word is a portmanteau of the words "volcanic", "smog", and "fog".