Meteorologist B.P. Yadav says the smog is created by a phenomenon known as atmospheric inversion, caused by a warming of the upper layers of the atmosphere that then traps and holds colder air on the surface and, with it, vehicular and industrial emissions, Inter Press Service reported Monday.
"The immediate result of the phenomenon is severely reduced visibility that throws flight schedules out of gear, as also the movement of trains and road vehicles," Yadav said. "The phenomenon should not be mistaken for plain fog which forms with plain moisture and high humidity."
The dense smog, common between November and January, can bring on health problems in the city of 15 million people, experts say.
"There is a marked rise in respiratory ailments in the winter months due to smog and it can also aggravate heart problems," cardiologist K.K. Aggarwal says.
Aggarwal, an advocate on public health issues, said people have forgotten the killer "London Fog" that claimed some 5,000 lives in 1952.
"Many industrial countries had since that tragedy adopted ambient air quality standards to protect the public from such pollutants as sulphur and nitrogen oxides, suspended particulate matter and carbon monoxide released by burning fossil fuels," Aggarwal said.
"India, sadly, does not enforce these norms."
Acute respiratory diseases reported in the city increased 28 percent between 2005 and 2008, Anumita Roy Choudhury of the Center for Science and Environment said.
"The government will need to take really strong measures to address air pollution," Choudhury said.