We present Mobile Observatory, a mobile air quality monitoring application that provides evaluation of air quality of the city of Zurich, Switzerland. As Mobile Observatory utilizes air quality data gathered by sensors mounted on around 10 trams in Zurich, it is able to provide neighborhood-level air quality information within the city. In this paper, we introduce a mobile air quality monitoring application Mobile Observatory. Also, we describe a user study with 10 participants and show our preliminary results in hopes of yielding insights toward improving civic and urban engagement on air quality.