Exploiting several key characteristics of quantum cascade (QC) lasers, including wide tunability and room-temperature operation, the Quantum Cascade Laser Open-Path System (QCLOPS) was designed for the detection of a range of trace gases and for field deployment in urban environments. Tunability over a wavelength range from 9.3 to 9.8 µm potentially provides the capability for monitoring ozone, ammonia, and carbon dioxide, a suite of trace gases important for air quality and regional climate applications in urban environments. The 2008 Olympic Games in Beijing, China drew attention to air quality problems in urban environments. Prior to and during the Olympic games, regional air quality modifications through factory shutdowns, car restrictions, and construction halts in Beijing and its surrounding areas created a unique test bed for new sensor technologies such as the QCLOPS sensor. We report the design of this novel, open-path air quality sensor and the results of both laboratory tests and field trials during the 2008 Olympic Games in Beijing, China.