In China's big cities these days, the air pollution can get so bad you hardly see things right in front of you — like buildings, cars, and pedestrians.
But there is something you are increasingly likely to see on city streets: people wearing respiratory masks.
Huang Wei is one of them. She works in Beijing for the environmental group Greenpeace. I caught up with her as she was about to bike home from the office one afternoon.
She checked the air quality on her smart phone. The pollution level was extremely high.
"It's not good for exercising,” she said.
So Huang strapped on a white face mask with a little plastic valve on the front. Technically speaking, it is a respirator – the sort of thing you might pick up at your local hardware store and wear at home when doing some sanding or painting.
Out on the street in Beijing, it didn’t take me long to find more people wearing them.
A woman who identified herself as Lina said she picked up the habit of wearing a mask “because the smog here is so heavy and the environment is not very good."
But she said she doesn’t like having to take this precaution, because the masks can get kind of grungy and smelly.
“It smells like bad eggs,” she said.
Respirators are designed to keep pollution, smelly or otherwise, from getting into the lungs. Of biggest concern are tiny particles — most Beijingers are very familiar by now with the scientific name for them, PM 2.5, which refers to particulate matter smaller than 2.5 micrometers. When it comes to human health, PM 2.5 is nasty stuff that can cause breathing problems and damage the heart and other organs.
Some manufacturers claim that their masks will remove more than 90 percent of those tiny particles. But for the masks to work right, they have to fit nice and snug — with no gaps on the sides — and people don't always wear them properly. Some people also wear the wrong kinds of masks, such as simple surgical masks, that do not filter out the fine particles.
Even if the right mask is worn correctly, however, “it’s not [full] protection,” said Tong Zhu. He's a professor of environmental science and engineering at Peking University.
“I would say that [a mask] is useful for a certain level” of pollution, Tong said. On really bad air days, when particulate levels are extremely high, he said it is probably worth putting on a mask – especially for children, the elderly, and people with health problems.
But when I asked him if he ever wore a mask, Tong's answer surprised me.
“No,” he said. “I never use that.” Tong said he finds respirators too inconvenient and uncomfortable to make a habit out of putting one on.
Besides, questions remain about whether all the masks are really as effective as advertised. Professor Tong is currently conducting a study to find out.
But for some Beijingers, effectiveness clearly isn't their sole concern.
Out and about during recent days, I've seen people wearing respirators in funky colors and fabrics. One even looked like a teddy bear’s face.
On the subway, I met a young woman sporting a mask in an attractive herringbone pattern. She told me that the first reason she bought it was for protection. The second: as a fashion statement.