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Haze in the Sichuan Basin, as seen from space

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Much like the Los Angeles basin, China's Sichuan Basin traps haze and smog. NASA's Terra satellite capture the following image of a hazy Sichuan Basin on January 23, 2014:

The Sichuan Basin is home to many cities, including the province's capital Chengdu, a city with more than 14 million residents.

Haze is trapped in the basin because of a temperature inversion. The same process that gives us beautiful fog in the Grand Canyon also works for pollutants. Earth Observatory explains:

Haze in this region tends to worsen in the winter, when cold, heavy air traps pollutants near the surface. In this case, the haze was likely trapped in the Sichuan Basin by a temperature inversion. Normally, air is warmest near the surface of the Earth. Occasionally, a mass of warm air will move over cooler air so that the atmosphere actually warms with altitude. Since the cool air does not have the energy to rise through the warm air, vertical circulation slows and air becomes trapped near the surface.

Any pollutant that enters the air gets trapped as well, and haze builds up over time. Temperature inversions often form in basins and valleys because surrounding higher-elevation land helps contain cold air. Daily imagesof the Sichuan Basin show that that the pollution has persisted for several days.

For a look at what the Basin looks like without a blanket of haze you can head over to Google Maps.

The views expressed are those of the author and are not necessarily those of Scientific American.

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