AsianScientist (Aug. 6, 2012) – A new study by NASA scientists published in the journal Science has revealed that up to 70 percent of the dust reaching North America comes from Asia.
Unlike pollution particles emitted close to the ground, high-altitude dust particles are less of a concern for human health, but their impact on climate can be significant.
With a 3D view of the atmosphere now possible from satellites, the scientists calculated that 64 million tons of dust, pollution, and other particles survive a trans-ocean journey to arrive over North America each year.
This is nearly as much as the estimated 69 million tons of aerosols produced domestically from natural processes, transportation, and industrial sources.
“This first-of-a-kind assessment is a crucial step toward better understanding how these tiny but abundant materials move around the planet and impact climate change and air quality,” said lead author Hongbin Yu, an atmospheric scientist at the University of Maryland and NASA’s Goddard Space Flight Center.
Observing these microscopic airborne particles and quantifying their global impact on warming or cooling Earth remains one of the most difficult challenges of climate science. Dust and pollution particles rise into the atmosphere and can travel for days across numerous national boundaries before settling to Earth.
Combining wind speed data with data retrieved from NASA’s Terra satellite and the Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observations (CALIPSO) satellite, Yu and colleagues estimated that dust crossing the Pacific Ocean accounts for 88 percent, or 56 million tons, of the total particle import to North America every year.
Global aerosol transport models revealed that Asia was a primary source of the dust reaching North America, contributing up to 60 to 70 percent of dust. The remaining 30 percent to 40 percent comes from Africa and the Middle East.
Dust particles are fine pieces of minerals that primarily come from dry, desert-like regions. Winds lift these lightweight particles high into the atmosphere where they meet even faster-moving winds capable of transporting them around the planet.
In contrast, pollution particles from combustion sources such as wildfires and fossil fuel burning are emitted close to the ground, and are hazardous to human health.
Although high-altitude dust particles are less of a concern for human health compared to pollution particles, they have a significant impact on climate.
One such impact is a cooling effect, brought about by dust and some pollution particles that reflect sunlight back to space. The team calculated that the imported particles account for one third of the reduction in solar radiation, or solar dimming, over North America.
“Globally this can mask some of the warming we expect from greenhouse gases,” said co-author Lorraine Remer, an atmospheric scientist at University of Maryland.
According to Remer, climate change brought about by greenhouse gases could influence the relevance of dust in the future. Desertification and reclamation will have a big impact on particle distribution and climate around the planet, she said.
The article can be found at: Yu H et al. (2012) Aerosols from Overseas Rival Domestic Emissions over North America.
Source: NASA; Photo: NASA Earth Observatory/Jeff Schmaltz.
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