Dust is a Worldwide Pollutant

by Jack Dini

What connects Earth's largest, hottest desert to its largest tropical rain forest? For the first time, a NASA satellite has quantified in three dimensions how much Saharan dust makes the trans-Atlantic journey. Scientists have not only measured the volume of the dust, they have also calculated how much phosphorus—remnant in Saharan sands from part of the desert's past as a lake bed—gets carried across the ocean from one of the planet's most desolate places to one of its most fertile. (1)

The trans-continental journey of dust is important because of what is in the dust. Specifically, the dust is picked up from the Bodele Depression in Chad, an ancient lake bed where rock minerals composed of dead microorganisms are loaded with phosphorus. Phosphorus is an essential nutrient for plant proteins and growth, which the Amazon rain forest depends on in order to flourish. The plus side: the phosphorus that reaches the Amazon soils from Saharan dust, an estimated 22,000 tons per year, is about the same amount as that lost from rain and flooding. (1)

Besides the dust from the Sahara, dust comes from the other direction, namely Asia. The biggest pollutant coming out of Asia, at least in terms of shear mass, could be dust form the region's swelling deserts. About every three years, a huge dust storm over China sends enormous clouds across the Pacific. Chinese dust has obscured vistas in US national parks, even on the East Coast. (2)

About 50 percent of aerosols in North America come from overseas, primarily dust and pollution from trans-Pacific transport, and also a little but of dust from trans-Atlantic transport from Africa. (3)

What is the key take-away from all of this? There has been concern about an emerging Asian economy and the increased pollution that will influence North American air quality and climate. But researchers have found that dust makes large contributions here. So we cannot just focus on pollution. We need to consider dust. The take-home message is that this is a small world and we share one atmosphere. Every country is influencing other countries' back yard, observes NASA scientist Hongbin Wu. (3)

References

1. “NASA satellite reveals how much Saharan dust feeds Amazon's plants,” nasa.gov/topics, February 24, 2015

2. David Kirby, “Ill Wind Blowing”, Discover, April 2011

3. “Q&A with atmospheric scientist Hongbin Yu,” nasa.gov/topics, August 2, 2012