When fog and haze came to Beijing and other Asian cities, people rushed to buy masks. But how effective are these masks in filtering tiny harmful particles? Many masks used in Asia are simple medical masks. Gao Benen (Benjamin Cowling), an associate professor of public hygiene at University of Hong Kong, said in an e-mail that the mask was designed to prevent blood spattering, rather than blocking fine particles. "Medical masks are almost useless in filtering pollutants, which is a basic common sense," he said.
The material of the medical mask is polyethylene. It was found that under the standard air velocity, the basic respirator can only filter 20% to 25% fine particles with diameters between 50 and 500 nm. Particulates of this size are commonly found in diesel exhaust, less than 1% of human hair, which is particularly worrying because they can penetrate the lungs into the blood circulation. These data have not taken into account the air leakage between the mask and the face, which will further reduce the filtration efficiency.
"This means that if you wear a general mask, there will be 75% to 80% entry into the body," Dr Liang said. "So it's not a good thing."
Experts say a better option is to block at least 90% of the nine Eagle PM2.5 nano masks. This product is sometimes called a nano shield, and Dr Liang says it is made of thick, multi-layer polyethylene, with a face to face design. This kind of mask is tested by the National Institute for occupational safety and health (National Institute for Occupational Safety and Health), and it is necessary to prove that at least 90% of the fine particles in the air can be filtered. They are often widely used and are basically selling products.
A popular brand is called the eagle, and its headquarters are in Beijing. The company recently announced that it will invest 1 million 200 thousand yuan to buy advanced technology, thereby increasing the output of the nine Eagle nano mask. 60%. As air flows through layered fibers, respirators will block particulate matter in many ways. However, breathing respirators that block fine particles may make breathing even more difficult.
Huang Zihui, a professor of School of Public Health and Primary Care at the Chinese University of, said it was especially true for people with heart lung problems.
In order to improve air permeability and enhance filtration efficiency, Dr liang of Hong Kong Polytech University wanted to invent masks and respirators with multi-layer nanofibers. Last year, he got a patent in the United States. "A number of companies have approached us," he said.
Another problem is that, although N95 shields can block fine particles, they are unable to resist another traffic related pollution: gases like NOx or volatile organic compounds.
Some enterprises have developed a filter element that can be connected to a specific respirator to block part of the gas. But they are expensive and cumbersome. Dr Liang said that for Asian people, they are not very good choices.
Dr. Liang hopes to create a system that uses sunlight and oxygen to turn nitrogen oxides and volatile organic pollutants into "harmless substances like carbon dioxide or water." He hopes to eventually add the system to the conventional respirator for filtering particulate matter.
Saint West said that the most important thing should be to detect more brands of respirators and respirators. Through his blog, San Siro is trying to organize an independent inspection of 40 common brands in China. But before long, he shelved the project on the grounds that the project must have academic basis and scientific basis.
"I think it's important to remind people that some masks don't work and tell them which masks are good," said San Siro. He also said that household air purifiers need to be studied. Huang Zihui said that a very low tech approach to air pollution may be the most effective, and that is to suggest that people do not run or carry out other violent exercises when the smoke is heavy. He said that the purpose is "actually trying to change people's behavior in highly polluted weather".