This paper presents an outdoor IoT-based air quality monitoring testbed deployed in the city of Uppsala, Sweden. Our IoT sensing unit is designed and developed using low-cost hardware components and open source software, which makes it easy to replicate. We demonstrate that it can serve as an affordable solution for real-time measurements and has potential to complement traditional monitoring to cover larger areas. We use low-power communication based on IEEE 802.15.4, RPL, and MQTT, and achieve high end-to-end delivery ratio (>98%) in an outdoor setting. Moreover, we carry out network analysis of our testbed and provide detailed insights into its characteristics.