Atmospheric dust, especially air-conditioner dust in urban-industrial environments, can act as a significant sink for both black carbon and nanoparticles posing allied health risks to the air conditioner repairman as well as to local inhabitants. However, the chemical composition of black carbon/nanoparticles in air-conditioner dust and their association with potentially toxic elements remain uncertain. The present study investigate the black carbon and nanoparticles compositions of air-conditioner dust and their associated potentially toxic elements, as an indicator of indoor air-pollution. The black carbon and nanoparticles in air-conditioner dust, were comprehensively characterized using array-based techniques including inductively Coupled Plasma-Mass Spectrometry, particle size distribution, Scanning Electron Microscopy, Transmission electron microscopy along with Energy-dispersive X-ray spectroscopy and selected area-(electron) diffraction, from metropolitan area of Hefei, China. Geo-accumulation index values of air-conditioner dust reveal Lead, Tin, Arsenic and Cadmium are under Geo-accumulation Classes V-VI level of contamination. The majority of the particles were found to be in the ultrafine nanoparticles range (<100 nm). A strong correlation was found between black carbon and total potential toxic elements content (R-2 = 0.79). The metallic nanoparticles (Iron, Copper and Lead) and black carbon were identified using Scanning Electron Microscopy/Transmission electron microscopy along with Energy-dispersive X-ray spectroscopy/selected area (electron) diffraction mode. Using array-based techniques seems to be a useful tool to study the black carbon and nanoparticles in air-conditioner dust. It is the first demonstration presenting evidence for the concept of air-conditioner dust as a sink for black carbon/nanoparticles bound potentially toxic elements in the urban-industrial environments, as an ultimate source of environmental pollutants. (C) 2018 Elsevier Ltd. All rights reserved.