Holographic Urban Environments (HUE) is a mixed reality visualization of real-time data from weather stations that displays the air quality levels and flow in urban spaces. The spatio-temporal data is mapped onto 3D printed physical models of three case-study cities (Beijing, London and New York City). We employed a combination of 3D printed models, Unity game engine and HoloLens headset for the workflow. The collapse of digital particle flow information onto physical models in a mixed reality environment suggests potentiality of intermixing information and visualizations of systematic flows that we are not able to see with our naked eyes.