Graphs dirty air worldwide
In many developing countries, the absence of surface-based air pollution sensors makes it difficult, and in some cases impossible, to produce air pollution graphs and maps. In these regions there is not even a rough estimate of the abundance of a subcategory of airborne particles that epidemiologists suspect contributes to millions of premature deaths each year. The problematic particles, about about a tenth the diameter of a human hair are 2.5 micrometers or less in diameter. These small particles can get past the body’s normal defenses and penetrate deep into the lungs. They are known as fine particulate matter (often abbreviated PM2.5).
To fill in these gaps in surface-based measurements of fine particulate matter, experts have looked to satellites. Yet, satellite instruments have until recently been inadequate when it comes to taking accurate measurements of fine particles in near-surface air. Most satellites can't distinguish particles close to the ground from those high in the atmosphere. In addition, certain factors such as clouds, snow, and desert sand can interfere with measurements.
However, the view got a bit clearer this summer with the publication of the first long-term global map of fine atmospheric particulates in a recent issue of Environmental Health Perspectives. Canadian researchers Aaron van Donkelaar and Randall Martin at Dalhousie University, Halifax, Nova Scotia, Canada, 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.
Their map of fine-particle air pollution graphs patterns worldwide. It shows the average satellite results between 2001 and 2006 and offers the most comprehensive view of these health-sapping particles to date. The new blending technique has provided the first fine particle air pollution estimates for many developing countries.
The map shows very high levels of fine particle pollution in a broad band extending from the Saharan Desert to to eastern Asia. Wind storms in the Arabian Desert and the Sahara raise huge quantities of fine particles into the atmosphere. Fortunately, almost no one lives in these sandy wastelands. But much of the heavily polluted band shown on the map is in fact densely populated. So much so that the data suggests that more than 80 percent of the world's population breathe polluted air exceeding the World Health Organization's recommended level of 10 micrograms per cubic meter.
Levels of fine particulate matter are comparatively low in the United States, though noticeable pockets are clearly visible over urban areas in the Midwest and East.
"We still have plenty of work to do to refine this map, but it's a real step forward," said Martin, one of the atmospheric scientists who created the map."We hope this data will be useful in areas that don't have access to robust ground-based measurements."