Washington: Using satellite data of almost 10 years, University of Illinois atmospheric scientists have documented some surprising trends in aerosol pollution concentration, distribution and composition over the Indian subcontinent.
In addition to environmental impact, aerosol pollution, or tiny particles suspended in the air, can be detrimental to human health by causing a range of respiratory problems.
Aerosols can come from natural sources, such as dust and pollen carried on the wind, but the most hazardous aerosols are generated by human activity – soot and other hydrocarbons released from burning various fuels, for example.
"The man-made aerosols tend to have a nastier effect on human health. Once we have a handle on how much, and the factors that influence the amount of aerosols that can build up, we can propose emission regulations," said Larry Di Girolamo, a professor of atmospheric sciences at U. of I.
Aerosol pollution levels can be measured on the ground, but only the most developed countries have widespread sensor data.
Standard satellite imaging cannot measure aerosols over land, so Di Girolamo worked with NASA to develop the Multi-angle Imaging Spectro-Radiometer (MISR).
Launched onboard NASA`s Terra satellite platform in 1999, MISR`s unique multi-view design allows researchers to differentiate surface variability from the atmosphere so they can observe and quantitatively measure particles in the air.
"Ten years later, we are mapping the globe in terms of particle properties. We`ve gone beyond just the amount of aerosols. We also can tell what kind of particles they are – how much is dust, how much is manmade," said Di Girolamo.
Di Girolamo and postdoctoral scientist Sagnik Dey recently conducted a 10-year comprehensive analysis of MISR data of aerosol pollution over the Indian subcontinent.
The densely populated region lacks on-the-ground monitoring sites, so until recently researchers could only guess at aerosol distribution over the area, where air quality is known to be poor.
"This study has shown that the level of atmospheric pollution across most of the country is two to five times larger than what the World Health Organization guidelines call for – and it`s home to one-sixth of the world`s population," said Di Girolamo.
The MISR data show very high levels of both natural and manmade aerosol pollutants in the air over the Indian subcontinent, but the longitudinal study also revealed some surprising trends.
For example, the researchers noticed consistent seasonal shifts in manmade versus natural aerosols. The winds over the subcontinent shift before the monsoon season, blowing inland instead of out to sea. The air quality during the pre-monsoon season is notoriously bad as these winds carry an immense amount of dust from Africa and the Arabian Peninsula to India.
"Just before the rains come the air gets really polluted, and for a long time everyone blamed the dust, but MISR has shown that not only is there an influx of dust, there`s also a massive buildup of manmade pollutants that`s hidden within the dust," said Di Girolamo.
The MISR data also revealed an especially dense area of manmade particles in India`s Gangetic Basin, in the foothills of the Himalayan Mountains.
This raises questions about the effects that soot and other particles may be having on weather patterns and water sources for the entire region.