Sunday 28 December 2008

Brown Clouds, Haze on Pollution Watchlist

Scientists say a brown cloud layer blankets huge areas of the planet, including China, threatening the climate and human health.

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Guanyu said...

Brown Clouds, Haze on Pollution Watchlist

Scientists say a brown cloud layer blankets huge areas of the planet, including China, threatening the climate and human health.

Li Hujun and Cheng Han, Caijing
26 December 2008

China’s environmental scientists and climate researchers are closely watching the sky.

And what some of them see, according to a United Nations Environment Program (UNEP) report on global pollution and climate change, are brownish cloud layers hovering over Chinese cities including Beijing, Shanghai and Shenzhen, blotting out the sun, reducing visibility and damaging human health.

A number of Chinese scientists contributed to international research that led to the November 13 release of the report entitled Atmospheric Brown Clouds.

“The scientific circle is getting to know the ABC phenomenon, but this is just a start,” said Shao Min, an environment professor at Peking University who participated in the project. “It’s feared that brown clouds, in addition to greenhouse gases in the atmosphere, pose a major threat to weather systems and humans.”

Asian Clouds?

The pollution layer was first observed during a field study called the Indian Ocean Experiment in 1999. A belt of brownish haze three kilometers thick was discovered over parts of the Indian Ocean and South Asia, including southern China, blanketing an area as big as the United States.

The cloud consisted of minute particles and gases. Mixed in the pollution layer were sulphates, nitrates, ammonium salt, black carbon and sand dust.

India and China protested against the original name for the phenomenon – “Asian brown clouds” – coined in a 2002 UNEP report. Scientists heeded the protest and renamed the layers “atmospheric brown clouds.” They’ve since acknowledged that the clouds can occur in North America, Europe, southern Africa and the Amazon River Basin.

“Brown clouds do not appear in Asia alone,” said Shi Guangyu of the Institute of Atmospheric Physics, Chinese Academy of Sciences, who led the push for a name change. “If they are called Asian brown clouds, China and India would come under great international pressure.”

Still, the clouds have been a focus of intense study across Asia. Scientists are interested in the high-flying haze due to the region’s variable climate, but especially because Asia is home to around half the world’s population and is undergoing massive growth.

Dimmer Cities

The skies in many big Chinese cities, particularly in the heavily industrialized Pearl River Delta, seem to have darkened in recent years. Days of low visibility have been on the rise. Now, scientists say brown clouds are mainly to blame.

The UN report said minute particles in brown clouds can absorb or reflect 10 to 25 percent of the sunlight that should reach a city’s streets. The report singled out as an example the Pearl Delta city of Guangzhou, where soot and dust have reduced natural light 20 percent since the 1970s.

Toxic aerosols and carcinogens float over the delta, including particulates less than 2.5 microns in width that are top contributors to low visibility, according to studies of regional atmospheric conditions conducted by Zhang Yuanhang and his team at the Environment Department of Peking University.

But standards for these tiny particles do not appear in China’s national air quality regulations. And the so-called “inhalable particles” mentioned in the Chinese media’s daily air quality reports only refer to particles smaller than 10 microns.

What’s happening in the Pearl River Delta reflects the overall deterioration of the nation’s air. The UN report said the sun’s warmth on the ground in China has decreased 3 to 4 percent every decade for the past 50 years. The situation has particularly worsened since 1970s.

Another region with poor air quality is the Yangtze River Delta, which reported a daily aerosol pollution record on January 19, 2007. Visibility fell below 600 meters as haze covered nearly the entire delta, including Shanghai. It was hard to breathe.

Shanghai’s air pollution index that day soared to 413 – nearly nine times the level recommended by the World Health Organization. It hit 500 on April 2.

But haze also envelops Beijing, Tianjin and other cities. Zhuang Guoshun, director of the Atmospheric Chemistry Research Center at Fudan University, said some cities are wrapped in haze more than one-third of the year. Weather forecasters now describe conditions as clear, cloudy, overcast or hazy.

The latest UNEP report identified 13 cities worldwide as brown-cloud hot spots. Three are in China: Beijing, Shanghai and Shenzhen. But Zhuang said clouds over China stretch far beyond to cover a region from Beijing south to Zhengzhou and Xi’an, as well as the coastal cities of Shanghai and Guangzhou. In addition, the western cities of Urumqi and Lanzhou are seriously affected.

Indeed, scientists say brown clouds can stretch over areas even larger than eastern China.

Deadly Risk

Breathing such toxic mixes of pollutants can be deadly. The UN report said about 340,000 people in China and India die each year from cardiovascular and respiratory diseases linked to concentrations of 2.5 micron particles that can be traced coal-fueled factories, diesel trucks and wood burning.

Pollution also hurts the economy. Economic losses tied to outdoor exposure to ABC-related particulates has been roughly estimated at 3.6 percent of GDP in China and 2.2 percent in India.

Apart from impacts on air quality and human health, the report said, brown clouds are in some regions aggravating the impact of greenhouse gas-induced climate change. Globally, however, brown clouds are blunting global warming by reflecting sunlight and absorbing heat. This is because ABCs contain particles such as black carbon and soot that absorb sunlight.

Eliminating brown clouds overnight could trigger a global temperature rise of as much as 2 degrees Celsius, which is considered by many scientists a dangerous threshold.

The scientific study of ABCs, which is interwoven with investigations of greenhouse gases, is not simple. These cloud conditions may contribute to highly complex warming and cooling patterns witnessed in different regions of China. For example, some fear they’ve changed the country’s East Asian monsoon climate system, while worsening droughts in the north and floods in the south.

Scientists suggest ABC-related heating of the atmosphere may be as important as greenhouse gas warming in accounting for retreating glaciers in China. The Academy of Sciences estimates these glaciers have shrunk 5 percent since the 1950s, while the combined size of China’s nearly 47,000 glaciers has fallen by 3,000 square kilometers over the past quarter century.

Other ABC-related phenomena may be waiting to be discovered. That’s one reason why Chinese scientists are calling for the nation’s leaders to give increased attention to brown clouds. Another reason is that millions of lives are at risk.