The invention is a filter for gaseous media in which nano alumina fibers and second fibers are arranged in a matrix to create asymmetrical pores. The filter is a high efficiency, high capacity particulate filter that intercepts pathogens and other particulate matter from gaseous media, including vapor-suspended particles. The new filter has an improved retention of water-aerosolized particles as compared to conventional HEPA filters and may be used as a pre-filter that extends the life of HEPA filters by about five to ten times. The invention is also a method of manufacturing and using the filter.