Peroxy radical detection for airborne atmospheric measurements using cavity enhanced absorption spectroscopy of NO2.

Development of an airborne instrument for the determination of peroxy radicals (PeRCEAS - Peroxy Radical Cavity Enhanced Absorption Spectroscopy) is reported. Ambient peroxy radicals (HO₂ and RO₂, R being an organic chain) are converted to NO₂ by adding NO, and are recycled through subsequent reaction with CO and O₂, thus forming a chain reaction with an amplification factor called chain length. The concentration of NO₂ is measured by continuous-wave cavity ring-down spectroscopy (CRDS) using an extended cavity diode laser at 409nm. Optical feedback from a Vshaped cavity optimizes resonator transmission and allows for a simple detector set up. CRDS directly yields absorption coefficients, thus providing NO₂ concentrations without additional calibration. The optimum 1δ detection limit is 0.3ppbv at an averaging time of 40s and an inlet pressure of 300mbar, corresponding to a concentration of 2 × 10⁹ molecules cm^-3. The calibration of the PeRCEAS chain length at an inlet pressure of 300mbar yields a value of 120 ± 7. The peroxy radical 1δ detection limit for an averaging time of 120s and a chain length of 120 is ~ 3pptv. [ABSTRACT FROM AUTHOR]