We studied primary emissions and secondary organic aerosol (SOA) from gasoline direct injection (GDI) vehicles including GDIs retrofitted with gasoline particle filters (GPF). GPF retrofitting significantly decreased the primary particulate matter, particularly through removal of refractory black carbon and, to a lesser extent, of non-refractory organic particulates. SOA experiments were conducted in a batch and flow reactor. GPF retrofitting did not significantly affect precursors or yields.