Satellite traces huge
pollution pool over Bihar
A study in the US has found
high pollution levels over much of India, and a concentrated pool of particles over
Bihar, reports PRAKASH M SWAMY
What is India News Service
March 1, 2005
NEW YORK: Scientists studying satellite data have discovered an immense wintertime pool of pollution over Bihar. Blanketing around 100 million people, primarily in the Ganges Valley, the pollution levels are about five times larger than those typically found over Los Angeles.
According to scientists, the discovery was made by researchers analyzing four years of data collected by the Multi-angle Imaging Spectro-Radiometer (MISR) onboard the Terra satellite. Lofted into orbit on Dec. 18, 1999, Terra is the flagship of NASA’s Earth Observing System Program.
“This study is the most comprehensive and detailed examination of industrial, smoke and other air pollution particles over the Indian subcontinent to date, and reveals how topography, meteorology and human activity help determine where these particles are concentrated,” said Larry Di Girolamo, a professor of atmospheric sciences at the University of Illinois at Urbana-Champaign and a co-investigator on the MISR mission. “MISR is the first instrument to make high-resolution, multi-angle radiometric measurements of Earth from space,” Di Girolamo said. “By measuring reflected sunlight at nine angles, we can accurately determine the amount of particulate matter, including that generated from man-made pollution, in the atmosphere.”
While high pollution levels were found over much of India, a concentrated pool of particles was discovered over Bihar, a largely rural area with a high population density.
A large source contributing to the Bihar pollution pool is the inefficient burning of a variety of bio-fuels during cooking and other domestic use. Particles in the smoke remain close to the ground, trapped by valley walls, and unable to mix upward because of a high-pressure system that dominates the region during winter. “The result is a pollution episode that can affect both human health and local climate,” Di Girolamo said. “The airborne particles can damage delicate lung tissue, and by altering the radiative heating profile of the atmosphere, the particles may change temperature and precipitation patterns.
”Prior to the MISR study, atmospheric models had predicted a tongue of pollution extending across the middle of India. The MISR observations, however, show the pollution lies much farther north. “These models are very important to us, as they are used to forecast pollution episodes and climate change,” Di Girolamo said. “The fact that model results don’t match the MISR observations suggests there are problems in the models or the model inputs that need to be fixed.”
The role of airborne particles remains one of the largest uncertainties in atmospheric modeling. In addition to modifying local climate, the particles can interact with clouds and change the cloud properties. This is particularly important, since clouds have the greatest radiative forcing on the climate system. “The Bihar pollution pool must be having a tremendous impact on the local climate and the health of the approximately 100 million people that reside within this pool.” Di Girolamo said.
“Our long-term goal is to better predict the occurrence of these pollution episodes and their impact on public health and local climate.” The work, funded by NASA, involved collaborators from Illinois, the Jet Propulsion Laboratory, the National Center for Atmospheric Research and Scripps Institution of Oceanography. The researchers published their findings in the December issue of the journal Geophysical Research Letters.
Scientists believe during certain seasons, as much as half of the ozone pollution above the Atlantic Ocean may be speeding down a "train" track of air from the Indian Ocean. As it rolls along, it picks up more smog from air peppered with thunderstorms that bring it up from the Earth's surface. Bob Chatfield, a scientist at NASA's Ames Research Center, Moffett Field, Calif. said, "Man-made pollution from Asia can flow southward, get caught up into clouds, and then move steadily and rapidly westward across Africa and the Atlantic, reaching as far as Brazil."
Chatfield and Anne Thompson, a scientist at NASA's Goddard Spaceflight Center, Greenbelt, Md., used data from two satellites and a series of balloon-borne sensors to spot situations when near-surface smog could "catch the train" westward several times annually from January to April.
During those periods of exceptionally high ozone in the South Atlantic, especially during late winter, researchers noticed Indian Ocean pollution follows a similar westward route, wafted by winds in the upper air. They found the pollution eventually piles up in the South Atlantic. "We've always had some difficulty explaining all that ozone," Thompson admitted.
Seasonal episodes of unusually high ozone levels over the South Atlantic seem to begin with pollution sources thousands of miles away in southern Asia," Chatfield said. Winds are known to transport ozone and pollutants thousands of miles away from their original sources. Clearly defined individual layers of ozone in the tropical South Atlantic were traced to lightning sources over nearby continents. In addition to ozone peaks associated with lightning, high levels of ozone pollution came from those spots in the Sahel area of North Africa where vegetation burned. However, even outside these areas, there was extra ozone pollution brought by the Asian "express train."
The scientists pinpointed these using the joint NASA-Japan Tropical Rainfall Measuring Mission satellite to see fires and lightning strikes, both of which promote ozone in the lower atmosphere. Researchers also identified large areas of ozone smog moving high over Africa using the Total Ozone Mapping Spectrometer satellite instrument.
The scientists confirmed the movement of the smog by using sensors on balloons in the Southern Hemisphere Additional Ozonesondes (SHADOZ) network. A computer model helped track the ozone train seen along the way by the SHADOZ balloon and satellite sensors. The scientists recreated the movement of the ozone from the Indian Ocean region to the Southern Atlantic Ocean. Their research results appear in an article in a recent issue of the American Geophysical Union's Geophysical Research Letters. The mission of NASA's Earth Science Enterprise is to develop a scientific understanding of the Earth system and its response to natural or human-induced changes to enable improved prediction capability for climate, weather, and natural hazards.
Prakash M Swamy, Ph.D (USA) is Editor-in-Chief, The Urban Indian newsweekly, The Empire State Building, 350 Fifth Avenue, #2612, New York.
He contributes regularly to The Indian Analyst