A new generation of portable standalone air cleaners relies on photocatalytic oxidation, plasma generation and microbial thermal inactivation. These technologies can generate potentially harmful byproducts, including volatile organic compounds (VOCs), ozone, ultrafine particles (UFP) and/or reactive oxygen species. Emissions originating from six portable air cleaners were investigated using a 20-m3 room-sized environmental chamber under realistic conditions. Pollutant concentrations were determined with the air cleaners operating in clean air and in the presence of a challenge VOC mixture. Four devices removed between 8% and 29% of VOCs at rates between 600 and 1700 ?g h-1, while the other two emitted VOCs at rates of 300 Ã¢â‚¬â€œ 1400 ?g h-1. Two devices showed good particle removal efficiency, reducing the UFP number concentration by 35% to 90%. Primary emissions (e.g., 85 ?g h-1 toluene) and secondary oxidation byproducts (e.g., 16 ?g h-1 formaldehyde) were observed. One device emitted very high ozone levels (up to 6 mg h-1), which also produced UFP in the presence of VOCs, reaching concentrations of 3 x 103 particles per cm3. Modeling results using chamber-derived emissions rates suggested that ozone emitted by one device can exceed regulatory levels. Formaldehyde emissions were predicted to exceed California reference exposure levels for three devices, and benzene emissions were predicted for two devices to exceed Proposition 65 risk levels.