Abstract
Abstract. Development of an airborne instrument for the determination of peroxy radicals (PeRCEAS – peroxy radical chemical enhancement and absorption spectroscopy) is reported. Ambient peroxy radicals (HO2 and RO2, R being an organic chain) are converted to NO2 in a reactor using a chain reaction involving NO and CO. Provided that the amplification factor, called effective chain length (eCL), is known, the concentration of NO2 can be used as a proxy for the peroxy radical concentration in the sampled air. The eCL depends on radical surface losses and must thus be determined experimentally for each individual setup. NO2 is detected by continuous-wave cavity ring-down spectroscopy (cw-CRDS) using an extended cavity diode laser (ECDL) at 408.9 nm. Optical feedback from a V-shaped resonator maximizes transmission and allows for a simple detector setup. CRDS directly yields absorption coefficients, thus providing NO2 concentrations without additional calibration. The optimum 1σ detection limit is 0.3 ppbv at an averaging time of 40 s and an inlet pressure of 300 hPa. Effective chain lengths were determined for HO2 and CH3O2 at different inlet pressures. The 1σ detection limit at an inlet pressure of 300 hPa for HO2 is 3 pptv for an averaging time of 120 s.
Highlights
The hydroperoxy radical (HO2) and organic peroxy radicals (RO2, R being an organic chain), hereafter referred to as peroxy radicals, are known for their importance in photochemical reaction cycles both in the stratosphere (Thrush et al, 1998) and troposphere (Monks, 2005)
NO2 is detected by continuous-wave cavity ring-down spectroscopy using an extended cavity diode laser (ECDL) at 408.9 nm
Accurate calculation of peroxy radical mixing ratios demands the knowledge of both the effective chain length (eCL) and the NO2 mixing ratio difference xNO2 introduced by the peroxy radical conversion
Summary
The hydroperoxy radical (HO2) and organic peroxy radicals (RO2, R being an organic chain), hereafter referred to as peroxy radicals, are known for their importance in photochemical reaction cycles both in the stratosphere (Thrush et al, 1998) and troposphere (Monks, 2005). A highly sensitive chemical method using chemiluminescence detection is the reaction of NO2 with a luminol (3-aminophthalhydrazide: C8H7N3O2) solution (Maeda et al, 1980) This yields excellent (3σ ) detection limits for the total sum of peroxy radicals of 3 ± 2 pptv (eCL = 45 ± 7, pressure 200 hPa, averaging time 20 s, Kartal et al, 2010) and it has been used in numerous measurement campaigns, both ground-based (Cantrell et al, 1993; Clemitshaw et al, 1997; Burkert et al, 2001b; Andrés Hernández et al, 2001; Fleming et al, 2006; AndrésHernández et al, 2013) and airborne (Green et al, 2002; Andrés Hernández et al, 2010; Kartal et al, 2010). Ring-down measurements taken during the background yield τ0 and those taken during the amplification mode yield τα in Eq (4)
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