Engineered nanoparticles (ENPs) released into the environment have a high probability of interacting with other pollutants before human exposure. These interactions can modify the physicochemical characteristics of ENPs' surface functionality. The toxicity of ENPs can thus largely depend on the coatings picked up in the environment rather than particle core alone. We built a dynamic system to simulate this barely-studied scenario and open up a novel and convenient way to form hydrophobic coatings directly on airborne ENPs. We coated airborne ENPs with low-volatile organic compounds (LVOCs)—common pollutants that exhibit a high affinity for surfaces. Measurement of airborne particle size distribution showed an increase in particle size after coating. The coating thickness was adjustable by controlling the parameters of LVOC generator, namely the reaction temperature and the flow rate through LVOC reservoir, to create 5–90 nm coatings. Transmission electron microscopy images and nanotracking analyses of ENPs suspended in liquid were used to further characterize the coating thickness. Both methods suggested that the system yielded stable, replicable, and well controlled surface coatings. ROS generation of the coated ENPs significantly depended on the type and thickness of LVOC coating. Chemically nonreactive coatings led to significantly reduced ROS generation of silver-ENPs with a 20 nm inert coating quenching close to 100% of ROS generation; this was attributed to the blocked reactive zones on the ENP surfaces. Chemically reactive anthracene coatings, in contrast, first passivated the surface but then contributed
to the redox cycle, leading to an increased generation of ROS, which was at a 90 nm coating thickness comparable to that of bare ENPs. Our results add to the understanding of ENP surface functionality—an important aspect of nanotoxicity. Furthermore, the high controllability of our ENP coating system makes it useful for other applications in inducing hydrophobic coating on airborne ENPs.