Low temperature combustion (LTC) has been shown to yield higher brake thermal efficiencies with lower NOx and soot emissions, relative to conventional diesel combustion (CDC). However, while demonstrating low soot carbon emissions it has been shown that LTC operation does produce particulate matter whose composition appears to be much different than CDC. The particulate matter emissions from dual-fuel reactivity controlled compression ignition (RCCI) using gasoline and diesel fuel were investigated in this study. A four cylinder General Motors 1.9L ZDTH engine was modified with a port-fuel injection system while maintaining the stock direct injection fuel system. The pistons were modified for highly premixed operation and feature an open shallow bowl design. RCCI operation was carried out using a certification grade 97 research octane gasoline and a certification grade diesel fuel. To study the particulate matter emissions from RCCI operation, particle size distributions were measured with a Scanning Mobility Particle Sizer (SMPS) and total particulate concentration in the exhaust was determined using membrane filters. The gas phase emissions were measured using both conventional emissions analyzers and an MKS FTIR analyzer. Emissions results are presented for engine out operation as well as catalyst out from a diesel oxidation catalyst. It was found that while RCCI yields a near zero smoke number (i.e., black carbon soot), there is a significant amount of particle mass being produced. These particles appear to be partially composed of volatiles because they are reduced by a second-stage of heating and dilution.