Worldwide deterioration of air quality has raised people's concerns on what they inhale on a daily basis. This work exploits inexpensive pollution sensors deployed in the Macao Polytechnic Institute service fleet as a mean to monitor air quality at city scale. We propose web-based geo-spatial exploration tool to provide air-quality information for users and insights on the causes to the city hall. We are able to identify strong connections between the territory orography and the air quality level. Specifically, it is possible by analyzing various areas to discover that places with traffic congestion and confined space, or poor natural ventilation which exhibits a sudden change in air quality readings.