SMOG is set to become an increasing cause of illness and death around the world as a result of climate change, a study has shown.
Scientists predict that 55 per cent of the global population could be affected by outbreaks of smog characterised by regions of stagnant "dead" air.
"Atmospheric stagnation events" were also expected to lengthen by the end of the century, increasing by up to 40 days a year across most of the tropics and sub-tropics.
Stagnation occurs when a non-moving air mass hangs over an area for an extended period, posing a serious pollution threat and leading to soaring rates of heart and lung disease.
Each year, poor air quality causes an estimated 2.6 million to 4.4 million premature deaths around the world, the researchers pointed out.
US scientist Dr Daniel Horton, from Stanford University, and colleagues wrote in the journal Nature Climate Change: "The potential public health impact increases as the duration of stagnation lengthens.
"Multi-day stagnation episodes can lead to prolonged hazardous air exposure associated with extreme air pollution, sever outbreaks of acute cardiovascular and respiratory illness, and increased incidence of mortality."
Warmer temperatures were expected to cause more smogs through changes in air circulation and the water cycle.
The prediction was based on a collection of climate models and assumed carbon emissions to remain high.
India, Mexico and the western US were said to be most at risk from health impacts due to smogs affecting areas of high population.