Dust Dominates Foreign Aerosol Imports to North America

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Aug. 2, 2012

Steve Cole 
Headquarters, Washington 
202-358-0918 
stephen.e.cole@xxxxxxxx 

Kathryn Hansen 
Goddard Space Flight Center, Greenbelt, Md. 
301-286-1046 
kathryn.h.hansen@xxxxxxxx 

Nicole Ruediger 
University of Maryland, Baltimore County 
410-455-5791 
nruedige@xxxxxxxx 

RELEASE: 12-262

DUST DOMINATES FOREIGN AEROSOL IMPORTS TO NORTH AMERICA

WASHINGTON -- NASA and university scientists have made the first 
measurement-based estimate of the amount and composition of tiny 
airborne particles that arrive in the air over North America each 
year. With a 3-D view of the atmosphere now possible from satellites, 
the scientists calculated that dust, not pollution, is the main 
ingredient of these imports. 

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. The results were 
published Aug. 2 in the journal Science. 

"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. 

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. 

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. Pollution particles, in 
contrast, come from combustion sources such as wildfires or 
agricultural fires and fossil fuel burning for power and industry. 
These particles are emitted close to the ground, making them of prime 
interest to air quality researchers and managers. High-altitude dust 
particles are less a concern for human health, but their impact on 
climate can be significant. 

One such impact on climate 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," says Lorraine Remer, an atmospheric scientist at 
University of Maryland, Baltimore County, and co-author on the study. 


Climate change brought about by greenhouse gases could influence the 
relevance of dust in the future, according to Remer. "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," she says. 

The study poses new questions about the magnitude of the particles' 
indirect effects on local weather and climate. Dust and pollution 
could alter wind circulation, foster cloud growth and affect rainfall 
patterns. Soot and dust particles that land on snow, most likely in 
the western United States, could speed the melt of the snowpack and 
affect water supplies. 

To see a video and images related to this study, visit: 

http://www.nasa.gov/topics/earth/features/dust-imports.html 

	
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