This study evaluates the potential of polymer aerogel monoliths in removing airborne nanoparticles. Macroporous monolithic aerogels of 8-form syndiotactic polystyrene (sPS) are synthesized for this purpose via thermoreversible gelation of a solution of sPS in a good solvent followed by supercritical drying. The air permeability and airborne nanoparticle removal efficiency are determined as function of the bulk density of aerogels. The data reveal a power-law dependence of particle removal efficiency and air permeability on bulk density. The data also reveal that efficiency greater than 99.95% can be achieved if the bulk density is kept at 0.042 g/cm(3) or higher. These materials show air permeability of the order of 10(-10) m(2), The gradient density aerogels produced via sequential injections of sPS solutions show improvements in filtration efficiency attributed to additional skin layers. This idea is exploited in designing gradient density aerogel filters that offer higher efficiency and higher air permeability at a much lower bulk density than the single density monoliths of the same thickness. (C) 2015 Elsevier B.V. All rights reserved.