哪种口罩防雾霾,我们需要仔细甄别

When smog descends on Beijing or other Asian cities, people rush to buy face masks.
当雾霾降临到北京等亚洲城市的上空时，人们争相购买口罩。

But how effective are the masks at filtering out tiny, harmful particles of pollution?
可是，在过滤微小的有害颗粒物方面，这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.
基于类型、品牌和贴合度等因素，它们的有效性千差万别。美国食品与药品管理局(United States Food and Drug Administration)称，松垮地戴在脸上的简单口罩在对抗污染上起不到什么作用，而如果是获政府审批的更为先进的呼吸防护罩紧贴在面部，则能起到作用，但或许不太舒适。卫生领域的专业人士称，在口罩方面亟需加强公众教育与研究。

"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."
为纽约时报国际生活网站撰写月度健康专栏的圣西睿智医生(Richard Saint Cyr)在北京执业，他通过电子邮件接受采访称，“消费者对哪些口罩最好完全是一头雾水。有些的确是会帮倒忙，比如人们获得了错误的保证，戴着不起作用的口罩在室外待更长的时间。”

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.
亚洲各地采用的许多口罩就是简单的医用口罩。香港大学公共卫生学副教授高本恩(Benjamin Cowling)在电子邮件中表示，这种口罩的设计用途是防止血液飞溅之类的问题，而不是阻挡细颗粒物。“医用口罩在过滤污染物方面几乎无效，这是很基本的常识，”他说。

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
香港理工大学创新产品与科技研究所所长梁焕方(Wallace Leung)称，医用口罩的材料是聚乙烯。他做的实验发现，在标准空气流速下，基本款的口罩只能过滤20%到25%直径在50到500纳米的细颗粒物。这种尺寸的颗粒物常见于柴油车尾气中，直径不到人体毛发的1%，因为能深入肺部进入血液循环而尤为令人担忧。这些数据还没有考虑口罩与面部之间漏气的情况，而这种空隙会进一步降低过滤效率。

"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."
“这就意味着，如果戴的是一般口罩，就会有75%到80%进入人体，”梁博士说。“所以情况不太妙。”

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.
专家们表示，更好的选择是能阻挡至少95%细颗粒物的呼吸防护罩。这种产品有时被命名为N95防护罩，梁博士说它由厚厚的多层聚乙烯制成，采用紧贴面部的设计。在美国，此类面罩接受国家职业安全与卫生研究所(National Institute for Occupational Safety and Health)的检测，要想过关必须证明能过滤空气中至少95%的细颗粒物。它们常被工业工人使用，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.
一个广受欢迎的品牌叫3M，厂家的总部位于明尼苏达州。公司最近宣布，将投资1500万美元（约合9300万元人民币）在新加坡新建一座工厂，从而把N95防护罩的产量提升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个人安全部门的技术经理尼基·麦卡洛(Nikki McCullough)称，在中国等亚洲国家，由于人们在雾霾天气里要保护呼吸系统，“我们明显发现相关防护产品的销量增加了”。该公司称自己生产的一次性呼吸防护罩的价钱从30美分到6.7美元不等。