N90 mask can protect against coronavirus, N90 can filter non-oil particulate matter, filtering efficiency is 5% less than N95, this new coronavirus pneumonia if you can’t buy N95 mask, N90 is also an option. The U.S. National Institute for Occupational Safety and Health will be in the middle of the mask this layer of filter material is divided into the following three: First, N series, N represents non-oil-resistant, can be used to protect non-oil suspended particles, time limit of 8 hours; Second, R series, R represents oil-resistant, can be used to protect the non-oil and oil-containing particles, time limit of 8 hours; Third, P series, P represents the oil-proof, can be used to protect the non-oil and oil-containing particles, use of no time limit. There is no time limit for use. According to the minimum filtration efficiency of the filter material can be divided into N90, N95, N100 three grades, 90 and 95 on behalf of the filtration efficiency, according to the filtration efficiency of 0.5 μm particle diameter as a test flow rate of 85L / min, N90, N95 and N100 protection efficiency are 90%, 95% and 99.97% or more.