Pollutants eclipse Bihar skies, Ganga valley
Surajit Dasgupta / New Delhi , The Pioneer
Scientists studying satellite data have discovered an immense wintertime pool of pollution in the skies of Bihar. Blanketing around 100 million people, primarily in the valley of the Ganga, the pollution levels are five times larger than those typically found over a highly industrialised Los Angeles.
The discovery was made by researchers analysing four years of data collected by the Multi-angle Imaging Spectro-Radiometer (MISR) onboard the Terra satellite. Lofted into orbit on December 18, 1999, Terra is the flagship of NASA's Earth Observing System Programme.
"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," wrote Larry Di Girolamo, a professor of atmospheric sciences at the University of Illinois at Urbana-Champaign and a co-investigator on the MISR mission, to Biochemistry Institute, Pune and Brain, Institute of Science and Languages, New Delhi, in an e-mail.
"MISR is the first instrument to make high-resolution, multi-angle radiometric measurements of Earth from space," Di Girolamo told The Pioneer on phone.
"By measuring reflected sunlight at nine angles, we can accurately determine the amount of particulate matter, including that generated from man-made pollution," he said.
While high pollution levels were found over much of India, a concentrated pool of particles was discovered over Bihar. A large source contributing to the Bihar pollution pool is the inefficient burning of a variety of biofuels.
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 pollution 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 modelling. 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 will have a tremendous impact on the climate and the health of approximately 100 million people who 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," he pointed out.
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 have got their findings published in the journal Geophysical Research Letters.