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Scientists identify aerosols making up smoggy haze over Mexico City
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14:53, September 04, 2008

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U.S. scientists examining smog over the Mexico City have found that agricultural and cooking fires along with burning industrial waste contribute a surprising amount of pollution, according to a press release on Wednesday.

The scientists from the University of California in San Diego (UCSD) and six other institutions have sorted through the pall that hangs over the city to precisely identify aerosols that make up the smoggy haze, said the release issued by the UCSD.

This forensic work reported in two studies will help identify the sources of these persistent pollutants, which plague other mega cities in the world, the release said.

With this information, country leaders will be better able to develop policies that will effectively clear the air, said the release.

The Mexico City once topped lists of places with the worst air pollution in the world. Although efforts to curb auto and industrial emissions have improved air quality, tiny particles called aerosols still clog the air.

Using an instrument that can quickly read the size and chemical fingerprint of individual particles one-by-one in real time, the scientists saw a daily rhythm in the chemical makeup of the Mexico City's smog, the release said.

Metal aerosols spiked in the early morning, contributing up to 73 percent of the particles they measured. By afternoon, shifting winds swept these industrial emissions away but blew in smoke particles from fires set to clear agricultural fields or burning in the hills south of the city. Burned bits of biomass accounted for as much as 76 percent of the smallest particles when strong winds flowed directly from the fires, the scientists found.

Satellite images taken during the experiment show a swath of fires burning in the hills surrounding the Mexico City. By matching the types of smog bits they captured to the wind patterns each day, the team was able to attribute the afternoon influx of freshly burned biomass to these distant fires.

Winds picked up each morning after 11:00 am, blowing the industrial waste away and bringing smoke from the fires to the south, said the release.

Fuel burned by street vendors also contributes to smoke in the city as a lot of people use charcoal on the streets to cook their food, according to the release.

"Our instrument brings in a new level of precision by allowing us to identify high levels of specific pollutants that occur in transient peaks," said Kimberly Prather, professor of chemistry and biochemistry at UCSD.

Source: Xinhua



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