Pre-filters of air purifiers and respirators use physical and or chemical processes with fibrous pleated paper, foam, cotton, ionizers, activated charcoal, absorbents, chemicals, catalysts, etc. and clean the air to the designed level before it enters other filters for further purifications. Air-purifying equipment with pre-filters is used in buildings, transports, public areas, and industries. There are wide varieties of technologies and user-defined requirements for air pre-filters and therefore, there are no standardized regulations about the performance and effectiveness. Many commercial options for air pre-filters are available for the use of air filtration units at homes, workplaces, hospitals, hotels, transports, etc., and in the respirators used by individuals.