The concentration of gases in the atmosphere are constantly changing. Many gases exhibit diurnal and seasonal cycles with larger fluctuations over geological time scales. Due to anthropogenic activities since the industrial revolution, the concentrations of greenhouse gases in our atmosphere have reached record levels that have never been seen before. Quantification of gases in the atmosphere and from emissions sources is essential for understanding the role humans play on global climate change. Ground-based in situ and total-column measurements can record large time scale data sets from fixed locations around the world. More recently, satellite observations have allowed for measurements of the variation in gas concentration at remote locations and over larger geographic regions. Experimentally collected atmospheric profiles are essential for validating retrievals from total-column measurements. In situ measurements on stratospheric balloons are one way that this can be achieved.

The CALASET project is a joint research endeavour between University of Toronto and University of Alberta to construct a laser spectrometer for stratospheric balloon measurements of atmospheric gases. The infrared spectrometer uses a quantum cascade laser and a multi-pass Herriott cell to measure CO2 and N2O concentrations in situ, creating atmospheric profiles from the ground up to altitudes close to the edges of space.

Constructing a robust instrument that can operate over a wide range of ambient temperatures and atmospheric pressures can present extra challenges. The CALASET instrument was designed to operate in ambient conditions down to temperatures of -60°C and pressures of less than 10 mbar at the extremes during the flight. The first flight occurred in Timmins, Ontario on August 23, 2018 at 3:00 UTC lasting 11 hours and reached an altitude of 33 km. A detailed discussion of the development of our instrument and the flight campaign will be presented.