Meltblown technology has recently gained a lot of attention in the production of submicrometer fiber webs with a fiber size less than 1 mu m. Single layer polypropylene meltblown webs with fiber diameters ranging from 520 to 2100 nm were produced using nano and micro dies. To our best knowledge, there are no substantial data in the public domain on the filtration characteristics of single layer stand alone submicrometer meltblown webs and their comparison with micrometer sized webs. This paper focuses on the influence of fiber diameter on the filtration characteristics of standalone single layer submicrometer and micrometer sized meltblown webs. Submicrometer single layer webs showed higher filtration efficiency and a higher quality factor, whereas webs with fiber diameters more than a micrometer showed lower filtration efficiency and a lower quality factor.