Dust, not pollution is the main component of the airborne particles imported from North America, say researchers.
According to a new analysis of NASA satellite data, 64 million tons of dust, pollution and other particles that have potential climate and human health effects 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," Hongbin Yu, lead author of the study from the University of Maryland, College Park, and NASA's Goddard Space Flight Center in Greenbelt, Md., said.
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.
Data from several research satellites with advanced observing technology developed and launched by NASA enabled the scientists to distinguish particle types and determine their heights in the atmosphere.
They combined that information with wind speed data to estimate the amount of pollution and dust arriving over North America.
The scientists used data from instruments on NASA's Terra satellite and the Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observations (CALIPSO) satellite, a joint effort between NASA and the French space agency, Centre National d'Etudes Spatiales.
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.
Dust movement is particularly active in spring, when the rise of cyclones and strong mid-latitude westerlies boost particle transport across the Pacific.
Global aerosol transport models revealed Asia was a primary source of the dust reaching North America. Sixty percent to 70 percent comes from Asia and the remaining 30 percent to 40 percent comes from Africa and the Middle East.
The study has been published in the journal Science.