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Narrator:  New satellite data show that every year, 64 million tons of airborne particles

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arrive in North American airspace from foreign sources,

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almost as much those produced domestically.

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These particles are called aerosols, a broad term that includes particulate pollution,

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soot from fires, salt from the ocean, grains of pollen,

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volcanic ash, and dust from deserts.

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And as it turns out the vast majority of these imported aerosols are in the

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and arrive in North America via air currents over

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the Pacific Ocean.

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For years researchers have used increasingly powerful computer models to simulate the transport of

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aerosols around the globe. But we had no good way of measuring

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how much of this aerosol mass was produced at home and how much came from abroad,

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how much was pollution and how much was dust, or how high these particles

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were in the atmosphere, all important factors in assessing aerosols’

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impacts on air quality and Earth’s climate.

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Now a new analysis of NASA satellite data has given us some surprising answers.

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Remer:  The first was that half of the particles that are above North America

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come from someplace else. And that’s a big number, half.

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I wasn’t expecting anything like that. The second piece was

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that even though these particles are coming from someplace else, they come in high in the atmosphere.

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They’re not on the ground, so we’re not breathing them. And the third piece

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of the study I found really surprising, that most of it is dust

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and natural aerosol, not manmade aerosol. And again,

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that, that has implications for if you’re trying to control how much

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pollution goes from one continent to the next, from one country to the next,

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even if you turned off all the industry everywhere else, we would

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still have all these foreign particles in our air shed above us

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because it’s, it’s natural. But as it turns out,

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we should still keep focused on our own pollution in order to

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keep our air healthy because the particles that come from other places come high.

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Narrator:  Besides direct impacts on human health, we need to better understand how the

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movement of aerosols affect weather and climate.

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For example, some aerosols can change precipitation patterns by

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while other dust and soot particles can

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build up on snow surfaces and have local effects.

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Yu: That could make snow darker and

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easier to melt. So

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this could have a significant impact on the water supply

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of the Western U.S.   Narrator: The imported aerosols

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primarily reflect sunlight, resulting in a cooler

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Earth-atmosphere system that partly compensates for the larger warming effect

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of greenhouse gases. Some imported aerosols actually like dust

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and soot absorb sunlight and heat the local atmosphere.

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Yu: This could change atmospheric circulations

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and it could have a significant impact on weather and climate.

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I think the take home message is

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So, that's my