"In the U.S., respirators are approved by the United States National Institute for Occupational Safety and Health (NIOSH). NIOSH classifies particulate respirators into one of three main classes -- N (not resistant to oil), R (somewhat resistant to oil), and P (oil proof). NIOSH ratings are applied with particulate filtration efficiencies of 95%, 99%, and 99.97%; N95 respirators are commonly used to help reduce exposure from non-oily particulates, such as air pollution particulates."
"In the Chinese standard, particulate respirators are divided into two classes: KN and KP classes. KN class respirators only filter non-oily particles, such as dust, mist and microorganisms. Particulate air pollution is typically considered a non-oily particulate. KP class filter respirators can be used for both oily and non-oily particulates. China-approved respirators are also available with several filtration efficiencies: 90%, 95% and 99.97% efficiency. KN90 and KN95 respirators are commonly used to help reduce exposures to non-oily particulates such as air pollution particulates."
Please refer to the description from 3M: