A fast and precise chemiluminescence ozone detector for eddy flux and airborne application

Abstract

A commercially available dry chemiluminescence (CI) instrument for fast and precise measurement of ozone (O₃) is specified. The sensitivity is ~9000 counts s⁻¹ per ppbv of ozone. Its precision is entirely determined by the number of photons reaching the detector (being a photomultiplier), i.e. is quantum-noise limited. The relative precision (ΔO₃/O₃ in %) thus follows Poisson statistics and scales with the square root of the measurement frequency <i>f </i>and with the inverse O₃ mixing ratio: ΔO₃/O₃ &prop; <i>f</i>^0.5 · O₃^&minus;0.5. At typical O₃ mixing ratios between 10 and 100 ppbv (and 1 bar), the precision is 0.3–1.0% at <i>f</i> = 10 Hz. The maximum measurement frequency is 50 Hz. The mechanical and electronic set-up as well as the instrument performance is described. Recommendations on the adequate inlet tube configuration (inlet tube length, sampling flow) and on the way of calibration at stationary ground-based platforms and onboard aircraft are given.