哪種口罩防霧霾,我們需要仔細甄別大綱

When smog descends on Beijing or other Asian cities, people rush to buy face masks.

當霧霾降臨到北京等亞洲城市的上空時，人們爭相購買口罩。

But how effective are the masks at filtering out tiny, harmful particles of pollution?

可是，在過濾微小的有害顆粒物方面，這些口罩究竟有多少效果呢？

The effectiveness varies tremendously, depending on factors like type, brand and fit. Simple, loosefitting masks do little to combat pollution, according to the United States Food and Drug Administration, whereas more advanced, government-approved respirators that bind tightly to the wearer's face can help but may be uncomfortable. More public education and research are urgently needed about face masks, health professionals say.

基於類型、品牌和貼合度等因素，它們的有效性千差萬別。美國食品與藥品管理局(United States Food and Drug Administration)稱，鬆垮地戴在臉上的簡單口罩在對抗污染上起不到什麼作用，而如果是獲政府審批的更爲先進的呼吸防護罩緊貼在面部，則能起到作用，但或許不太舒適。衛生領域的專業人士稱，在口罩方面亟需加強公衆教育與研究。

"Consumers simply just don't know which of those masks are the best," Richard Saint Cyr, a physician in Beijing who writes a health column for the Chinese-language T Magazine once a month, said in an email. "And some indeed may be worse than helpful if people are falsely reassured and spend more time outside using a mask which doesn't work."

爲紐約時報國際生活網站撰寫月度健康專欄的聖西睿智醫生(Richard Saint Cyr)在北京執業，他通過電子郵件接受採訪稱，“消費者對哪些口罩最好完全是一頭霧水。有些的確是會幫倒忙，比如人們獲得了錯誤的保證，戴着不起作用的口罩在室外待更長的時間。”

Many masks worn around Asia are simple surgical-type masks. But these are designed to prevent problems like splattering blood, not to block tiny particles, Benjamin Cowling, an associate professor of public health at the University of Hong Kong, said in an email. "It is pretty common knowledge that surgical face masks have almost no filtration efficiency against pollutants," he said.

亞洲各地採用的許多口罩就是簡單的醫用口罩。香港大學公共衛生學副教授高本恩(Benjamin Cowling)在電子郵件中表示，這種口罩的設計用途是防止血液飛濺之類的問題，而不是阻擋細顆粒物。“醫用口罩在過濾污染物方面幾乎無效，這是很基本的常識，”他說。

Surgical masks are made of polypropylene, according to Wallace Leung, director of the Research Institute of Innovative Products and Technologies at the Hong Kong Polytechnic University. His tests found that at a standard airflow velocity, basic masks captured only 20 to 25 percent of tiny particles of 50 to 500 nanometers — a size common in diesel vehicles' exhaust. Such particles, less than 1 percent of the width of a human hair, are of particular concern because they can get buried deep in the lungs and end up in the bloodstream. The figures do not include any gap between the mask and the face that allows air to come in, further reducing efficiency

香港理工大學創新產品與科技研究所所長樑煥方(Wallace Leung)稱，醫用口罩的材料是聚乙烯。他做的實驗發現，在標準空氣流速下，基本款的口罩只能過濾20%到25%直徑在50到500納米的細顆粒物。這種尺寸的顆粒物常見於柴油車尾氣中，直徑不到人體毛髮的1%，因爲能深入肺部進入血液循環而尤爲令人擔憂。這些數據還沒有考慮口罩與面部之間漏氣的情況，而這種空隙會進一步降低過濾效率。

"What it means is, if you wear a face mask, you get 75 to 80 percent into the body," Dr. Leung said. "So that's not good."

“這就意味着，如果戴的是一般口罩，就會有75%到80%進入人體，”樑博士說。“所以情況不太妙。”

A better bet, experts say, are respirators that guard against at least 95 percent of small particles. Sometimes known as N95 respirators, they use thick layers of polypropylene, according to Dr. Leung, and are designed to fit tightly to the face. In the United States, such masks get tested by the National Institute for Occupational Safety and Health and must be shown to keep out at least 95 percent of all tiny airborne particles to gain approval. They are often used by industrial workers and are generally disposable.

專家們表示，更好的選擇是能阻擋至少95%細顆粒物的呼吸防護罩。這種產品有時被命名爲N95防護罩，樑博士說它由厚厚的多層聚乙烯製成，採用緊貼面部的設計。在美國，此類面罩接受國家職業安全與衛生研究所(National Institute for Occupational Safety and Health)的檢測，要想過關必須證明能過濾空氣中至少95%的細顆粒物。它們常被工業工人使用，基本是一次性用品。

One widely sought-after brand is 3M. The Minnesota-based company recently announced that it would invest $15 million in a Singapore plant to increase production of its N95 respirators by 70 percent.

一個廣受歡迎的品牌叫3M，廠家的總部位於明尼蘇達州。公司最近宣佈，將投資1500萬美元（約合9300萬元人民幣）在新加坡新建一座工廠，從而把N95防護罩的產量提升70%。

"We definitely are seeing an increase in sales for respiratory protection" for use in China and elsewhere in Asia during hazy conditions, said Nikki McCullough, the technical manager for 3M's personal safety division. The company said the price for its disposable respirators ranges from 30 cents to $6.70.

3M個人安全部門的技術經理尼基·麥卡洛(Nikki McCullough)稱，在中國等亞洲國家，由於人們在霧霾天氣裏要保護呼吸系統，“我們明顯發現相關防護產品的銷量增加了”。該公司稱自己生產的一次性呼吸防護罩的價錢從30美分到6.7美元不等。

The respirators block particles in a number of ways as the airflow encounters layered fibers. But respirators that guard against small particles can make it more challenging to breathe. That is especially true for people with heart or lung problems, said Tze-wai Wong, a research professor at the School of Public Health and Primary Care at the Chinese University of Hong Kong.

隨着氣流經過層狀纖維，呼吸防護罩會以多種方式阻擋顆粒物。不過，能阻擋細顆粒物的呼吸防護罩可能會讓呼吸變得更困難。香港中文大學公共衛生及基層醫療學院(School of Public Health and Primary Care at the Chinese University of Hong Kong)的黃子惠(Tze-wai Wong)教授表示，對有心肺問題的人羣尤其如此。

To improve breathability and increase filtering efficiency at the same time, Dr. Leung of Hong Kong Polytechnic University wants to create masks and respirators that use multiple layers of nanofibers. He received a United States patent last year, and "a number of companies have approached us," he said.

爲了改善透氣性，同時增強過濾效率，香港理工大學的樑博士想發明出使用多層納米纖維的口罩和呼吸防護罩。去年，他在美國獲得了一項專利。“已經有多家公司跟我們接洽了，”他說。

Another issue is that while N95 respirators guard against small particles, they do not combat another form of traffic-related pollution: gases like nitrogen oxides or volatile organic compounds.

另一個問題是，儘管N95防護罩能阻擋細顆粒物，它們卻無法抵禦另一種與交通有關的污染：像氮氧化物這樣的氣體或揮發性有機化合物。

Some companies have created cartridges that can connect to certain respirators to block some gases. But they are expensive and cumbersome — and, Dr. Leung said, not a good choice for the public in Asia.

一些企業已經研製出了能和特定的呼吸防護罩相連以阻擋部分氣體的濾芯。但它們很貴，而且很笨重。樑博士說，對亞洲的民衆而言，它們不是很好的選擇。

Dr. Leung hopes to create a system that uses sunlight and oxygen to turn nitrogen oxides and volatile organic compounds into "harmless substances, like carbon dioxide or water." Eventually, he hopes to be able to join it to a regular, particle-filtering respirator.

樑博士希望能製造一個用陽光和氧氣，將氮氧化物和揮發性有機污染物變成“像二氧化碳或水那樣的無害物質”的系統。他希望最終能把這個系統加進過濾顆粒物的常規呼吸防護罩中。

More testing of existing brands of masks and respirators should be a priority, Dr. Saint Cyr said.

聖西睿智表示，首要的應該是對現有的口罩和呼吸防護罩品牌進行更多的檢測。

Aided by his blog, Dr. Saint Cyr is trying to organize independent testing for 40 brands that are commonly available in China. But he recently put the project on hold, citing the need to gain academic and scientific backing for the project.

通過自己的博客，聖西睿智正試圖組織對中國常見的40個品牌進行獨立檢驗。但前不久，他擱置了這個項目，理由是必須讓這個項目有學術依據和科學依據。

"I feel it's very important to warn people against masks that don't work, as well as to tell them which work well," Dr. Saint Cyr said, adding that research is also needed on household air-purifying machines.

“我覺得提醒人們有些口罩不起作用，並告訴他們哪些口罩效果好很重要，”聖西睿智說。他還表示，也需要對家用空氣淨化器進行研究。

Dr. Wong said that one low-tech method of combating air pollution might also be the most effective — encouraging people not to go jogging or engage in other strenuous activities during times of heavy smog. The goal, he said, is "really to try to change the behavior of people on high-pollution days.”

黃子惠表示，對付空氣污染的一種科技含量很低的方法可能也是最有效的，那就是建議人們不要在煙霧濃重的時候跑步或進行其他劇烈運動。他說，目的“實際上是試着改變人們在高污染天氣中的行爲”。