觀塘兒童心肺病遠超沙田 能見度低日子佔全年50％ 污染物增 (明報) 09月 25日 星期二 05:10AM

【明報專訊】本港空氣污染問題近年備受關注，可持續發展委員會引用研究指出，每立方米空氣中各項污染物的總量每增加10毫克，市民患上各類污染影響兒童心肺功能，與空氣質素相對較佳的沙田 區比較，在污染情惡劣的觀塘區生活的兒童，罹患各類呼級疾病的機會較高，相差幅度由31%至98%不等。
可持續發展委員會在今年6月開始就未來空氣改善措施進行為期3個月的諮詢，截至上周五共接獲2萬多份回應，諮詢期將於下月中屆滿，結果將於12月公布。
空氣改善諮詢逾2萬份回應
身為委員會更佳空氣質素支援小組成員的譚一翔指出，本港能見度偏低的日子，已由10年前佔全年15％，大幅增至目前50％。當空氣中污染物數量增加，因患呼吸道疾病而死亡、入院及引致哮喘 個案數目，亦隨之上升。
譚一翔指出，空氣中有可吸入懸浮粒子、氮氧化物、二氧化硫等不同污染物，中大和港大多項研究顯示，每立方米空氣中各項污染物的總量每增加10毫克，市民患上各類呼吸疾病引致死亡的機會，會增加0.8％至3.4％。研究發現，在每立方米空氣中，二氧化硫每增加10毫克，因心臟病 引致的死亡率便增加2.8％；臭氧每增加10毫克，市民入院個案會增加2.2％。
2000年訪問數千兒童
本身為兒科醫生的譚一翔表示，中大在2000年一項有關空氣污染影響兒童心肺功能的研究，調查了數千名兒童，發現沙田區（低污染地區）兒童心肺功能較觀塘區（高污染地區）兒童為佳，兩者心肺功能指數，分別為29.9和27.8。
若以發病情計，觀塘區兒童患各項呼吸系統症狀較沙田區兒童為多，除鼻敏感及支氣管炎外，餘下8項呼吸系統症狀均以觀塘區兒童為多，多出比率由31%至98%不等。
譚一翔表示，呼吸道疾病是兒童較易患上的疾病，但近年未見明顯上升趨勢。對於近期有學校因空氣污染嚴重而更改運動會時間和日期，譚一翔表示，這反映了本港空氣問題嚴重。

Last Updated: Monday, 24 September 2007, 13:53 GMT 14:53 UK

Amazonian forest 'more resilient'
The Amazon rainforest may be more resistant to rising temperatures than has been believed.
Researchers found that during the 2005 drought, many parts of the rainforest "greened", apparently growing faster.
This finding contrasts with some computer models of climate change, which forecast that the Amazon would dry out and become savannah.
Writing in the journal Science, the researchers say it is unclear how the forest would respond to a long drought.
"We measured the changes between the drought (of July to September 2005) and an average year," explained study leader Scott Saleska from the University of Arizona, Tucson, US.
"And what we saw was that there was more photosynthesis going on, more capacity to take up carbon dioxide than in an average year," he told the BBC News website.
The scientists used the Modis (Moderate Resolution Imaging Spectroradiometer) instrument on the US space agency's (Nasa) Terra satellite to make their observations.
Some areas of the Amazon had seen reduced growth during the drought, but these were regions heavily impacted by human activities.
Clear skies
It has been thought that stressed trees in drought conditions would try to preserve their water by reducing loss through leaves (transpiration), with this shut-down having a consequent knock-on for photosynthesis.
This, in turn, would be expected to exacerbate the drought by interrupting the supply of water into the atmosphere, a supply which contributes to rainfall.
"Some of the models, in particular the Hadley Centre group (part of the UK Met Office), became famous for predicting collapse of the Amazon and a change into savannah," said Dr Saleska.
"There's a prompt response to the initial drought: trees down (transpiration), they release less water to the atmosphere so there's less to recycle as rain; and in that model world, it pushes the forest over the edge.
"We've tested whether that mechanism is there, and found it's not there on a short timescale. That doesn't mean the forest won't collapse, but it says that the scenario in that model is not right in that particular [situation]."
Although increased photosynthesis in drought conditions might appear counter-intuitive, the group said it could be explained if the trees were still able to access water reserves with deep root systems.
Persistent bright skies during a drought would allow more sunlight through to the leaves, driving photosynthesis and leading to the "greening" seen from space.
Model refinement
Chris Jones from the UK's Hadley Centre for Climate Change commended the study, and said it demonstrated the importance of using real-world observations to challenge and fine-tune the models.
He added that the Hadley and Saleska teams were sharing data.
The British researcher agreed that the satellite images showed up the short-term constraints of the Hadley model, but did not overturn the long-term predictions of his group.
"The key thing here is that the tree roots access water deeper than is often represented in models," he told BBC News.
"In most models, including ours, this goes down to about three metres, which for most of the world's vegetation is fine. But these (Amazon) trees can clearly go deeper than that, so while our model predicts they would suffer during a couple of months of drought, in reality they have access to a much deeper store which doesn't respond on that timescale."
He said, however, that a climatic shift to longer and more frequent drought conditions would eventually diminish the deep-water stores, and make the trees suffer.