Chemical storage rooms located near engineered nanomaterials (ENMs) workplaces can be a significant source of unintentional nanoaerosol generation. A new incidental nanoparticle source was identified and characterized in a chemical storage room located at an ENMs workplace. Stationary and mobile measurements using on-line instruments and chemical analysis of volatile organic compounds (VOCs) were carried out to identify the source. The number of nanoaerosols emitted from the chemical storage room was found to be several orders of magnitude higher than that existing in the ENMs workplace. VOC analysis showed that the accumulated precursors and oxygenated VOCs in the chemical storage room could be attributed to incidental particle formation via gas-to-particle conversion. We stress the importance of identification of the incidental nanoaerosols to allow characterization of the nanoaerosols at ENMs workplaces, and to estimate additional nanoaerosols exposure, which was previously unknown. Hazardous chemical substances in the workplace have been regulated in many countries; however, most of the regulations are focused on gas-phase or liquid-phase substances. The present study emphasizes the importance of secondary pollutants in particulate form that can be generated from the gas or liquid phase of hazardous chemical substances. (C) 2015 Elsevier B.V. All rights reserved.