The ABCs of haze. (Air Pollution).

Haze and airborne dust--the visible portions of air pollution--were once seen as minor irritants, but they are gathering force like a coming storm. In August 2002, the United Nations Environment Programme (UNEP) released The Asian Brown Cloud: Climate and Other Environmental Impacts, which describes a "new scenario" of air pollution in South Asia, involving haze, smog, ozone, and global warming. In September 2002, the CBS MarketWatch news website ranked the Asian Brown Cloud among 10 "mega-trends for 2003" in terms of its implications for health, business, and politics.

The term "Asian Brown Cloud" originally referred to a brownish soup of pollutants and particles over India, from forest fires, the burning of farm wastes, and huge increases in emissions from vehicles, industries, and woodburning cookstoves. But new satellite data from the National Aeronautics and Space Administration show that the Asian Brown Cloud is part of a much larger-scale pollution event encompassing most of East and Southeast Asia. The haze is heaviest between December and May, the main home-heating season, but is getting worse year-round.

The UNEP report was based largely on the Indian Ocean Experiment (INDOEX), conducted by scientists in the United States, India, and Europe (for more information on this project, visit http://wwwindoex.ucsd.edu/). INDOEX examined the movement of aerosols specifically over South Asia (comprising India, Pakistan, Bangladesh, and Sri Lanka). An INDOEX report in the 7 December 2001 issue of Science suggested that aerosols in the haze could seriously disrupt the Earth's cycle of evaporation and precipitation. By interfering with sunlight's breakdown of hydroxyl radicals, the haze could affect water availability and crop production.

The UNEP report draws preliminary conclusions about air pollution's effect on the South Asian environment and the implications for human health, agriculture, and climate change. For example, the report states that the haze reduces natural solar energy levels by about 10%, with significant consequences for farm yields--for rice planted in Hyderabad, India, shortly before the haze starts, the report estimates a 10% cut in rice yield. The report also cites figures for deaths worldwide related to air pollution: from a global estimate of 2.7-3 million deaths per year in 2001, the number could rise to 8 million by 2020.

The report spurred discussion of transboundary haze at the August 2002 World Summit on Sustainable Development held in Johannesburg, South Africa. In Asia, the report has kicked up dust of a different sort. Indian scientists take issue with the notion--implied, they said, by the phenomenon's name--that Asians are to blame for pollution, while Western countries have polluted the air for decades at far higher rates. Sulochana Gadgil, a professor at the Centre for Atmospheric and Oceanic Studies in Bangalore, also expresses doubts about the model used by UNEP. Gadgil considers the model unreliable, citing faults such as poor simulation of the rainfall patterns over Pakistan and Afghanistan.

V. Ramanathan, an atmospheric physicist at the University of California at San Diego and report coauthor, says the report does not seek to assign blame, but to raise awareness of the problem and its implications. Russell Schnell, director of observatories for the National Oceanic and Atmospheric Administration's Climate Monitoring and Diagnostics Laboratory in Boulder, Colorado, agrees that the report's importance lies in the public recognition that it has stimulated, and says the problem of transboundary pollution is likely to grow.

Schnell likens the phenomenon to a railway encircling the globe, with freight cars of pollutants that load and unload at points along the way: "When you get a trainload, you don't know exactly where all the pollution came from. It's an international, integrated problem."