Open-path ozone measurements performed by mid-IR differential absorption spectroscopy are reported. Ozone spectrum was taken by fast repetitive sweeping of a quantum-cascade laser wavelength over a spectral feature from the ν3 absorption band of ozone, centered at 1031.2cm-1. Short (100ns) sweeping times were essential to prevent line-distortions caused by atmospheric turbulence. For fast wavelength sweeping, a technique that employed the thermal chirp during 140ns excitation pulses was used. The lowest detection limit of 0.3ppm.m was estimated from the minimum detectable differential absorption. We present the results from cell and open-path measurements over 440 and 5800m, together with experimental data regarding the tuning range, the tuning rate and the tuning linearity of the QCL while operated with 140ns excitation pulse
