August 3, 2012
Foreign Dust And Airborne Aerosols Invade North America
[ Watch the Video: Imported Dust in American Skies ]
April Flowers for redOrbit.com - Your Universe OnlineIn a joint study between NASA and University of Maryland, College Park, scientists have made the first measurement-based estimate of the amount and composition of tiny airborne particles that arrive over North America each year. With a 3D view of the atmosphere now possible from satellites, the team calculated that dust, not pollution, is the main ingredient.
According to the analysis, published in the August 2, 2012 issue of Science, 64 million tons of dust, pollution, and other particles that have potential climate and human health effects cross the oceans to arrive in North America every year. This is nearly as much as the 69 million tons of aerosols produced domestically. Those domestic particles come 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," says Hongbin Yu, lead author and an atmospheric scientist at the University of Maryland, College Park, and NASA's Goddard Space Flight Center in Greenbelt, Md.
Dust and pollution particles can travel for days in the atmosphere, crossing many national boundaries before resettling to Earth, making observation and quantification of their impact rather difficult.
The team used data sets from several satellites, including NASA's Terra satellite and the Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observations (CALIPSO). CALIPSO is a joint effort between NASA and the French Space Agency, Centre National d'Etudes Spatiales (CNES). This allowed scientists to distinguish particle types and determine their heights in the atmosphere.
Yu and colleagues estimate that dust crossing the Pacific Ocean accounts for 88 percent, or 56 million tons, of the total particle import to North America every year. The bulk of this particle movement happens in the spring when the rise of cyclones and strong mid-latitude westerlies boost transport across the Pacific.
Asia seems to be the primary source of dust, weighing in at 60 to 70 percent of the total, with the remaining 30 to 40 percent coming from Africa and the Middle East.
What is the difference between dust and pollution, and why does it matter?
Dust particles are fine pieces of minerals that primarily come from dry, desert regions. Winds lift these lightweight particles high into the atmosphere where they catch even faster moving winds capable of transporting them around the planet. Pollution, on the other hand, comes from combustion sources such as wildfires or fossil fuel burning from industry. Pollution particles are emitted close to the ground, making them of prime interest to air quality researchers and health officials. High-altitude dust particles are less of a concern for human health, but their impact on climate is significant.
Dust particles can reflect sunlight back to space, creating a cooling effect on the climate. The team calculated that the imported particles account for one third of the reduction in solar radiation, or solar dimming, over North America. Climate change brought about by greenhouse gases could influence the relevance of dust in the future.
"Globally this can mask some of the warming we expect from greenhouse gases," says Lorraine Remer, an atmospheric scientist at University of Maryland, Baltimore County, and co-author on the study. "Desertification and reclamation, the land use modifications that change the exposure of dusty soils to wind erosion, are going to have a big impact on particle distribution and climate around the planet."
New questions arise from this study about the magnitude of particles and their indirect effects on local weather and climate. Dust and pollution could alter wind circulation, foster cloud growth, possibly affect water supplies and rainfall patterns.