"Anti-superfine particles mask" has become the most searched word in Google Vietnam in recent times. "Imported face mask" is also much searched.

The PM2.5 particulate (described as superfine particles with 3 percent the diameter of a human hair) level in Hanoi reached a five-year high last month, according to a government report released on Wednesday. The environment ministry warned that if people have to go out, they should wear masks and eyeglasses to reduce the exposure to pollutants.

A mask seller, who asked not to be identified, said last week’s sales were equal to last month’s.

Quynh Anh, another seller, said within a few minutes after she posted on a forum that she was selling Cambridge Mask she received hundreds of orders.

Her advertisement said the mask blocks most pollutants, including benzene, formaldehyde and PM2.5. It costs VND500,000-530,000 a piece ($22 – 23).

More premium brands include Vogmask of the U.S. that cost VND750,000-1.1 million ($32 – 47).

The product claims to filter at least 99 percent of airborne particles, including PM 0.3.

A Vogmask mask costs $32 – 47. Photo courtesy of Seetheair.

Trang of Hanoi, who did not reveal her last name, said she recently acquired 15 anti-particle masks from Singapore for VND 1.2 million ($52).

"Hanoi has been so polluted these days that I had to buy it even though it’s super expensive."

According to the sellers the masks can be washed and reused for two to five months.

Locally produced masks are also in demand.

For example, 3M brand masks costing VND25,000 - 50,000 claim to filter 95 percent of tiny particles of up to PM 0.3 size, bacteria and viruses.

Some environmental experts have sounded an alarm about the benefits these masks advertise.

But there is no official agency to certify or recommend quality anti-pollution masks to the public.

Doan Ngoc Hai, director of the Institute of Occupational Health and Environment, admitted this was a major problem.

Another expert, who asked not to be named, said wearing a mask does not guarantee safety from fine dust and bacteria, and most masks sold in the market only protects from normal dust and dirt.

The only one that does protect from fine dust particles and chemicals is an anti-gas mask, but it is heavy and inconvenient to wear, the expert said.

Depressing pollution

PM2.5 particles come from vehicles, industrial plants and natural sources like dust, and easily pass through lung tissue to be absorbed into the bloodstream, causing adverse health effects.

Worsening air quality, manifest in Hanoi and Ho Chi Minh City in recent days as a thick haze, has become a matter of great worry for their residents.

At 9 a.m. on Tuesday HCMC's air quality index (AQI) was measured at an "unhealthy" 159.

Increasing numbers of residents are suffering from respiratory diseases as the air quality plunges.

On the same morning Hanoi's index was 254, a level ranked "very unhealthy" at which people with respiratory or heart diseases are significantly affected and experience reduced endurance in activities.

The city has in fact this week consistently had the world’s worst air quality in a ranking of more than 10,000 cities worldwide.

Officials blame the low quality of air in the capital on construction, a growing number of cars and motorcycles and heavy industry, including steel works, cement factories and coal-fired plants.