To collect O3 profiles (i.e. vertical distribution), an O3 sensor is coupled to a radiosonde which measures pressure, temperature, humidity and wind. Using the Station's aerology facilities, ozonesondes were sent aloft once a day. O3 is present in the upper troposphere as a result of convective lofting of surface O3, and in situ production dominated by anthropogenic NOx, lightning NOx, and formaldehyde produced from surface isoprene emissions. The stratosphere is also a source region for tropospheric O3. During the 1997 program, a parachute (orange) was provided for each instrument. While parachutes are still in use for launches in human-populated areas, they have not since been used at Sable.