Two researchers working at Dalhousie University in Canada figured out how to measure a class of tiny airborne particles -- called fine particulate matter -- that are involved in asthma, heart disease, bronchitis and several other illnesses.
These particles are so tiny -- about a tenth of the diameter of a human hair -- that they can evade the body's defenses and penetrate the lungs and even the blood stream. In the U.S., according to the American Heart Association, they cause about 60,000 deaths a year.
But there are many more of them above Northern Africa and East Asia, according to this map, which was created by Aaron van Donkelaar and Randall Martin and shows the average estimate of these particles between 2001 and 2006. It was first published in Environmental Health Perspectives.
Some of the particles occur naturally -- the wind blows mineral dust, for instance, from the Arabian and Saharan deserts. Others are caused by humans -- there are sulfate and soot particles from power plants, nitrates from motor vehicle exhaust, and sooty black carbon from diesel engines and agricultural burning.
It's not clear yet how many of each type of particle show up on the map, but the map does show that they're there, even above developing countries with no ground-based air pollution sensors -- which have been the usual way of getting estimates.
From NASA, on how the map was made:
Most satellite instruments can't distinguish particles close to the ground from those high in the atmosphere. In addition, clouds tend to obscure the view. And bright land surfaces, such as snow, desert sand, and those found in certain urban areas can mar measurements.
...van Donkelaar and Martin created the map by blending total-column aerosol amount measurements from two NASA satellite instruments with information about the vertical distribution of aerosols from a computer model.
...In addition to using satellite data from NASA's Multi-angle Imaging SpectroRadiometer (MISR) that flies on NASA's Terra satellite and the Moderate Resolution Imaging Spectroradiometer (MODIS) instrument that flies on both NASA's Aqua and Terra satellites, the researchers used output from a chemical transport model called GEOS-Chem to create the new map.
NASA Goddard has more experiments planned to keep refining estimates of fine particulate matter -- this map could be about 25 percent off.
Still, it allows epidemiologists to hone in on countries with the most polluted air to study the health of the people who live there.
Here's a video from Goddard Space Flight Center of the global transport of black carbon -- i.e. soot.