Abstract
Abstract. An incoherent broadband cavity-enhanced absorption spectroscopy (IBBCEAS) technique has been developed for the in situ monitoring of NO3 radicals at the parts per trillion level in the CSA simulation chamber (at LISA). The technique couples an incoherent broadband light source centered at 662 nm with a high-finesse optical cavity made of two highly reflecting mirrors. The optical cavity which has an effective length of 82 cm allows for up to 3 km of effective absorption and a high sensitivity for NO3 detection (up to 6 ppt for an integration time of 10 s). This technique also allows for NO2 monitoring (up to 9 ppb for an integration time of 10 s). Here, we present the experimental setup as well as tests for its characterization and validation. The validation tests include an intercomparison with another independent technique (Fourier-transform infrared, FTIR) and the absolute rate determination for the reaction trans-2-butene + NO3, which is already well documented in the literature. The value of (4.13 ± 0.45) × 10−13 cm3 molecule−1 s−1 has been found, which is in good agreement with previous determinations. From these experiments, optimal operation conditions are proposed. The technique is now fully operational and can be used to determine rate constants for fast reactions involving complex volatile organic compounds (VOCs; with rate constants up to 10−10 cm3 molecule−1 s−1).
Highlights
25 The night time chemistry in polluted urban or sub-urban areas has been proved to be governed by NO3 radicals since its discovery in the 1980s (Naudet et al, 1981; Noxon et al, 1978, 1980; Platt et al, 1980)
NO3 radical has been shown to be an efficient oxidant for some organic compounds, or in some cases even the dominant one, impacting the budget of these species and their degradation products
Due to the high reactivity of some unsaturated VOCs with NO3, absolute rate determination for these reactions appears to be difficult as it requires the use of a highly sensitive method for NO3 monitoring
Summary
25 The night time chemistry in polluted urban or sub-urban areas has been proved to be governed by NO3 radicals since its discovery in the 1980s (Naudet et al, 1981; Noxon et al, 1978, 1980; Platt et al, 1980). Among the various experimental tools which are currently used to measure rate constants, atmospheric simulation chambers represent suitable tools for performing experiments under very realistic atmospheric conditions This implies low concentrations of reactants in order to minimize possible secondary reactions. Even though significant progresses have been made in the last decades for NO3 radicals measurement at low concentrations with the arising of cavity enhanced and cavity ring down spectroscopic techniques (Ball et al, 2004; Bitter et al, 2005; Kennedy et al, 2011; Langridge et al, 2008) as well as laser induced fluorescence techniques (Matsumoto et al, 2005b, 2005c, 2005a; Wood et al, 2003), it is 50 observed only few were coupled to simulation chambers (Dorn et al, 2013; Venables et al, 2006; Wu et al, 2014).In addition, to our knowledge, none of these techniques have been used for kinetic applications involving NO3 radical in simulation chambers.
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