Dust Dominates Foreign Aerosol Imports to North America

Aug. 2, 2012

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

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

Nicole Ruediger
University of Maryland, Baltimore County
410-455-5791
nruedige@umbc.edu

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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