Wednesday, Dec 10, 2003
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A YEAR AGO, the United Nations Environment Programme (UNEP) issued a report on the `Asian Brown cloud', creating the image of a vast blanket of pollution choking the Indian sub-continent. This cloud of aerosols created by human activity would, it was claimed, have disastrous effects on the climate, including on the monsoon rain. Aerosols, which are fine particles in the atmosphere, can be natural or humanmade. Winds whip up sand and dust from the ground, and also carry vast quantities of fine sea salt into the air. Motor vehicle fumes, and the burning of coal, other fossil fuels and biofuels such as wood, generate fine carbon particles. Emissions from industries can produce sulphate and nitrate particles. By scattering or absorbing the light coming from the sun or being reflected back into space from the Earth, these aerosols can have an impact on the climate. But such effects depend on the nature of aerosols present as well as their size and concentration. Aerosol levels, composition and geographical spread vary greatly from season to season and year to year. Natural aerosols may often predominate. So the question is whether the anthropogenic aerosols (that is, those generated by humans) are of such a level and kind that they have a significant impact on the climate in the way greenhouse gases are causing global warming.
The UNEP report left the impression that the `cloud' of anthropogenic aerosols from Asia was having such an impact. Indian scientists disagree, pointing out that erroneous conclusions were being drawn largely from a single data collection campaign over the Indian Ocean and that such forms of aerosol pollution were present in other parts of the world too. A paper by American researchers published recently in a scientific journal notes that pollution plumes off the east coast of the United States could be just as intense as those over India and other parts of Asia. Although there is greater recognition that the `atmospheric brown cloud' (as it is now called) is a global phenomenon, the focus on India and China as large contributors to humanmade, and by implication avoidable, aerosol pollution persists. Such concern is not without reason. The declining air quality in towns and cities across India is all too obvious. It is not just vehicles and industries that enhance aerosol levels in the air. It may be that the burning of dung, wood and other biological material poses a more widespread and less easily controlled problem.
India therefore needs a sustained research programme of its own to quantify and understand aerosols all over the country. The Indian Space Research Organisation has been studying this subject over the past two decades, but at just a few places. It has plans for a countrywide multi-institutional campaign next year to collect aerosol data using ground-based sensors. It is also known to be considering similar shipborne and aerial campaigns for a later stage. There have been press reports that the India Meteorological Department is to acquire ground instruments for continual aerosol measurements. Both steps are welcome. However, it would probably help to have a single overarching programme so that aerosol data collection and its utilisation for properly reviewed research projects across institutions can be coordinated and brought to bear on this problem. The Department of Science and Technology's successful Indian Climate Research Programme offers a good model. In any case, irrespective of the impact on the climate, identifying the sources of anthropogenic aerosols and taking steps to reduce their levels is an imperative if air quality is to be improved in India.
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