If the mask fits...

Beijing has become world famous for its smog. In January, there were only five days that were not heavily polluted. On Lantern Festival on February 24, the air turned foul again and the weather observatory issued a yellow fog warning. Until 9 pm, 25 out of the 35 monitoring stations in the greater Beijing area had PM2.5 pollution (particles smaller than 2.5 micrometers) values greater than 300 micrograms per cubic meter.

The danger of PM2.5 pollution is widely acknowledged. A study conducted by Peking University and environmental NGO Greenpeace published in December 2012 says air pollution led to 2,349 deaths in Beijing in 2010, and the authors estimate the number of deaths in 2012 to be 2,589.

Masks can shield against Beijing's smoggy air. However, not all masks sold on taobao.com or in corner stores can effectively fight the pollution. Metro Beijing talked to experts and Beijingers who have used masks, from the cheap cotton ones to the high-end ones in order to help you make sense of the spectrum of offerings on the market.

Novelty masks

The common, cartoon-adorned masks sold online or on the street, usually made with cotton and a layer of fuzz, can't really defend against the pollution. They're more fashion accessory than anything.

Wang Xiaojiao, a master's student at Beijing Forestry University, bought one with a cartoon bear design from a shop on Wudaoying hutong in Dongcheng district.

"I bought it to block out the cold air more than the pollution. It definitely can't compare with the other masks in terms of protecting you against PM2.5," she said.

Protection: The mask doesn't provide sufficient protection against the pollution; it's not specially designed to do so. But in terms of keeping your nose warm, you can bet on it.

Comfort: Since it's cotton, it's quite comfortable.

Breathing difficulty: The mask doesn't block breathing since it doesn't have filters. Air comes through to your nose quite easily.

Obstruction of vision: When you wear glasses, the steam from your breath can go up and obscure your vision.

Cost: About 5 yuan ($0.80)

Surgical mask

Many, especially medical doctors, have access to surgical masks. They are usually made from gauze or paper and used during surgeries in hospitals. But while these masks are great in keeping out dust and larger particles, they can't defend well against PM2.5.

Dr Richard Saint Cyr, a family medicine physician with the Beijing United Family Hospital, tried on many masks during the smoggy days of January, and said he doesn't believe the surgical masks are effective.

"If you are going to wear a mask, you might want to wear a proper mask. Wearing one of these doesn't prevent pollution from getting in very well," he said. "These masks don't really fit your face and there's still tons of air coming in from outside. It helps with blocking out viruses, but if you are blocking out PM2.5, it still needs to be a better fit."

Protection: Good protection against germs, but its efficacy against pollution is debatable due to the air that can leak in due to its one-size-fits all fit.

Comfort: Not comfortable. It's hot and stuffy and tugs on the ears.

Breathing difficulty: Blocks breathing a lot and you can't do any exercise while wearing it.

Obstruction of vision: None.

Cost: 2 yuan