Earth & Sky

Human activities found to increase urban haze

The haze that hangs over many cities originates in car exhaust and industrial activity. But it's helped along by invisible smog-forming gases in the atmosphere, which interact to form dangerous aerosols. (Daniel Cosman)

A scientific study of the air in Mexico City found that human activities contribute even more to the formation of urban haze than previously thought.

Jose–Luis Jimenez is a chemist at the Cooperative Institute for Research in Environmental Sciences at Boulder. He studied Mexico City’s haze. It’s true that a city’s haze orginates in car exhaust and industrial activity. But, in addition, invisible smog–forming gases react in the atmosphere to form hazy particles, or aerosols. These particles are dangerous to people. They’re believed to exacerbate heart and lung problems and to increase the risk of premature death.

Jose–Luis Jimenez: It’s not that people didn’t know that these processes could happen, in which gases become particles. It’s just that it was thought that it would happen much more slowly and to a much smaller extent.

Jimenez and his colleagues found concentrations of aerosols in urban air eight times greater than what had been predicted by typical air quality computer models. Jimenez said human activities greatly enhance the formation of these dangerous particles.

Jose–Luis Jimenez: If they can drive less, or drive cars that are more fuel efficient, or buy appliances that are more energy efficient, all of these things in the end come back to us.

Thanks today to NASA ; explore, discover, understand. We’re Block and Byrd for Earth & Sky.

Written by Jorge Salazar

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