Smog in cities: why?
Just over a month ago, Paris was in the news due to dangerously high levels of smog. Out of the many actions that could have been taken, government officials chose one known to work in the short but not in the long-run: license-plate driving bans. Mexico City, Beijing or Athens all implemented similar measures in the past but soon acknowledged failure. People bought a second, much cheaper and much more environmentally damaging car effectively ruining the efforts. But why are so many cities in the world, particularly those in less developed areas, plagued by noxious smog?
The safe limit of pollution particulates in the urban air is set at 80 micrograms per cubic metre. During the smog, levels reached 180 micrograms per micrograms in Paris with government officials starting to highlight the potential health damages.  After a week, however, the smog had left and Paris’ traffic went back to normal as well. Whether this had something to do with the driving ban is uncertain, experts believe that a favourable change in weather was the main reason for the relief. One thing is certain: the air Paris experienced a month ago had a quality level other people living elsewhere wished they could breathe in for just a week. Take New Delhi as an example, were pollution averaged 575 micrograms per cubic metre for over five months in 2013 – more than seven times the amount that is considered healthy. It currently is the world’s most polluted metropolis. Why do some cities experience smog while others don’t have this problem at all? Some cities are predestined due to their location. Mexico City is situated in a so-called highland “bowl” in which all polluting agents are effectively trapped – the main reason why this city suffers from recurrent smog. Back in the 20th century major cities like London suffered from pollution caused by coal firing. After the automobile revolution, transportation emissions became the main reason for urban smog formation. Today, coal and transport emissions have mostly vanished as smog provokers – at least in the Western world. But even here, they could return soon.
This is because another decisive player has emerged, one that won’t be battled by a week of limited car traffic. Global warming: when temperatures rise, smog lingers around longer because pollutants remain at the ground and so cannot escape. This is a particularly pressing problem in areas with little wind flow. So all in all, the most effective measure will be to lower the pollutants in the earth’s atmosphere. A rather great challenge that won’t be achieved by one country but only by collective action.