||
By staff reporters Li Hujun and Cheng Han
From Caijing Magazine
http://english.caijing.com.cn/2008-12-26/110042630.html
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
According to some scientists, brown clouds, in addition to greenhouse gases in the atmosphere, already 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
The cloud consisted of minute particles and gases. Mixed in the pollution layer were sulphates, nitrates, ammonium salt, black carbon and sand dust.
“Brown clouds do not appear in Asia alone,” said Shi Guangyu of the
Still, the clouds have been a focus of intense study across
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
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
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
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
But haze also envelops
The latest UNEP report identified 13 cities worldwide as brown-cloud hot spots. Three are in
Indeed, scientists say brown clouds can stretch over areas even larger than eastern
Deadly Risk
Breathing such toxic mixes of pollutants can be deadly. The UN report said about 340,000 people in
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
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
Scientists suggest ABC-related heating of the atmosphere may be as important as greenhouse gas warming in accounting for retreating glaciers in
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.
Archiver|手机版|科学网 ( 京ICP备07017567号-12 )
GMT+8, 2024-10-19 23:19
Powered by ScienceNet.cn
Copyright © 2007- 中国科学报社