Despite a number of smog chamber studies of the α-pinene/O3 system, the effect of temperature on α-pinene secondary organic aerosol (SOA) mass fractions (or yields) remains poorly understood. In this study, the temperature dependence of secondary organic aerosol mass fractions (AMF) during ozonolysis of α-pinene is investigated in a temperature controlled smog chamber. Experiments were performed with and without ammonium sulfate aerosol seeds at RH < 10% and at 0¿C, 15¿C, 20¿C, 30¿C and 40¿C. The initial α-pinene concentration varied from 3.5 to 50 ppb, and an excess of ozone was used. High time resolution secondary organic AMFs were obtained combining continuous gas-phase concentration measurements (using proton transfer reaction mass spectrometry, PTR-MS) with continuous aerosol concentration measurements (using a scanning mobility particle sizer, SMPS). The presence of inert aerosol seeds is often necessary to minimize experimental errors due to loss of semivolatile vapors to the walls of the chamber. The α-pinene secondary organic AMFs show a weak dependence on temperature in the 15¿ to 40¿C range and stronger temperature dependence in the 0¿ and 15¿C range.