A thermoplastic core-sheath fiber comprises: a polymer fiber core having a coextensive sheath layer disposed thereon, and an electrostatic charge enhancing additive. The sheath layer may comprise poly(4-methyl-1-pentene) and the fiber core and the sheath layer have different compositions. At least one of the fiber core or the sheath layer comprises an electret charge. A nonwoven fibrous web comprising the core-sheath fibers and a respirator including the nonwoven fibrous web are also disclosed.