Indian Murky Air Quality
Data from the Multi-angle Imaging Spectroradiometer (MISR) instrument on NASA's Terra spacecraft have been used in a groundbreaking new university study that examines the concentration, distribution and composition of aerosol pollution over the Indian subcontinent. The study documents the region's very high levels of natural and human-produced pollutants, and uncovered surprising seasonal shifts in the source of the pollution.
Armed with a decade’s worth of satellite data, University of Illinois atmospheric scientists have documented some surprising trends in aerosol pollution concentration, distribution and composition over the Indian subcontinent.
Technically, an aerosol is a suspension of fine solid particles or liquid droplets in a gas. Examples are smoke, oceanic haze, air pollution, and smog. Some man made aerosols, particularly sulfate aerosols from fossil fuel combustion, exert a cooling influence on the climate which partly counteracts the warming induced by greenhouse gases such as carbon dioxide. Recent research, as yet unconfirmed, suggests that aerosol diffusion of light may have increased the carbon sink in the Earth's ecosystem.
In addition to environmental impact, aerosols 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 many come from the effects of man.
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 man-made." Di Girolamo said.
Di Girolamo and postdoctoral scientist Sagnik Dey recently published a 10-year comprehensive analysis of MISR data of aerosol pollution over the Indian subcontinent in the Journal of Geophysical Research. 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," Di Girolamo said.
The MISR data show very high levels of both natural and man-made aerosol pollutants in the air over the Indian subcontinent, but the study also revealed some surprising trends. For example, the researchers noticed consistent seasonal shifts in man-made 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 man-made pollutants that’s hidden within the dust.” Di Girolamo said.
During the monsoon season, rains wash some of the dust and soot from the air, but other man-made pollutants continue to build up.
During the post-monsoon season, dust transport is reduced but man-made pollutant levels skyrocket as biomass burning and the use of diesel-fueled transportation soar. During the winter, seaward breezes disperse both natural and human-generated pollution across the subcontinent and far out to sea until the pre-monsoon winds blow again.
The MISR data also revealed an especially dense area of man-made 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. Di Girolamo and his team hope to continue to study the area and investigate the cause of the buildup.
As MISR continues to collect worldwide aerosol data — Di Girolamo expects up to another five years of orbit — atmospheric scientists can continue to refine models for India and other areas and begin to propose new regulatory measures. MISR may also reveal trends in aerosol concentration over time, which can be compared with climate and health data.
Industrialization and urbanization have resulted in a profound deterioration of India's air quality. Of the estimated 3 million premature deaths in the world that occur each year due to outdoor and indoor air pollution, the highest number are assessed to occur in India. According to the World Health Organization, the capital city of New Delhi is one of the top ten most polluted cities in the world.
NASA makes all MISR data freely available to the public, so its data can fuel research for many scientists for years to come. In addition, MISR’s success has inspired other multi-view-angle satellite projects around the world.
"I suspect if we jump 50 years into the future, multi-angle imagers like MISR will be the norm in terms of monitoring"” Di Girolamo said.
For further information: http://www.news.illinois.edu/news/10/0907aerosol_DiGirolamo.html