Geoscience Reference
In-Depth Information
Satellites are also being used to quantify PM movement between continents.
Hongbin Yu, an associate research scientist at the Goddard Earth Sciences and Tech-
nology Center, a joint research center of NASA and the University of Maryland Baltimore
County, and his colleagues found that East Asian pollution sources added an aver-
age of about 15% to the non-dust PM burden already being generated in the US and
Canada from 2002 to 2005. These fi ndings, published in the April 22, 2008
Journal
of Geophysical Research
, provide the fi rst satellite-based estimate of transport of PM
from East Asia to North America.
The study did not calculate the effects at ground level, which requires enhanced
satellite capability to assess on a daily basis vertical structures of pollution plumes
with high accuracy. “[That] process is still a bit fuzzy,” says Solar Smith, a research
associate at the Center for Space Research at the University of Texas at Austin, who
did not participate in the Yu study. “On a long-term scale, you can take the average
over time and get a fairly reliable understanding of how [ground-level] air quality is
changing. The challenge is individual scene analysis on individual days. We're always
working to improve algorithms.”
Using existing algorithms, an international team studied 26 locations in Sydney,
Delhi, Hong Kong, New York City, and Switzerland, and found an overall 96% corre-
lation between satellite measurements of atmospheric column PM loading and ground
measurements of PM concentration, although there was signifi cant variation caused
by factors such as cloud cover, relative humidity, and circulation within the boundary
layer. These results were published in the September 2006 issue of
Atmospheric
Environment
. In the June 2008 issue of the same journal, Klaus Schäfer and colleagues
reported a 90% correlation between satellite and ground measurements for fi ne par-
ticulates 2.5 μm in diameter or smaller (PM
2.5
) in the winter, but in the summer only a
48% correlation for PM smaller than 1 μm in diameter.
These variable results and those of other studies confi rm that there is indeed still a
bit of fuzziness in the processes of both measurement and calculation. The emerging
data from lidar (the optical analog of radar) measurements taken aboard the Cloud-
Aerosol Lidar and Infrared Pathfi nder Satellite Observation (CALIPSO) satellite will
help to get a clearer picture, says Yu. Satellite measurements with more extensive
coverage than CALIPSO are needed in the future. But the results are becoming reli-
able enough—at least in some regions and seasons—that a handful of local projects
are using or considering using PM data derived from satellites.
The HELIX-Atlanta (Health and Environment Linked for Information Exchange
in Atlanta, Georgia) is a 5-county demonstration project whose principal investiga-
tor for its fi rst half was Amanda Niskar, then with the Centers for Disease Control
and Prevention (CDC). The project's partners include NASA, the CDC, the EPA,
the Georgia Environmental Protection Division, Kaiser Permanente of Georgia,
the Georgia Institute of Technology, and Emory University. The goal is to improve
knowledge of the link between PM
2.5
and respiratory diseases among residents of the
5-county area and improve forecasting of dangerous PM
2.5
events as well as govern-
ment, medical, and individual responses to them. Eventually this information could be
extrapolated to other settings.
