似乎美国很热衷这方面的研究，矛头当然是指向中国和印度。不过，中国确实是污染够严重的。前段时间有报道说什么广州的空气富含阳离子啊，空气质量好什么的，被骂吹牛不靠谱。07年在广州呆一年，天一直都是灰色的，从来都看不到蓝天，晚上也看不到星星。

回到听力的内容，这一篇感觉听起来没前面三篇那么困难，看来奋斗一个月是有进步的。

Stanford University professor Mark Jacobson developed the first computer models to measure the presence of soot in the atmosphere. He calculates that soot accounts for between 15 and 20 percent of global warming.

His study, presented this week at the American Chemical Society meeting in Colorado, describes how black carbon - the main component in soot - heats up clouds when it mingles with the rain drops suspended within them.

"And it turned out that there is more heating when the black carbon was inside the drop than between the drops and there was more heating when the black carbon was between the drop than outside of the cloud. So the bottom line was you get this enhancement of the heating of the cloud by the black carbon presence in the cloud drops."

Jacobson says climate models that ignore this cloud absorption phenomenon underestimate the effects of black carbon in the atmosphere. His research found that airborne soot quickly burns off cloud cover.

"If you look at satellite images over really polluted areas such as in China and India you can actually see an absence of clouds."