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).
Sensing atmospheric reactive species using light emitting diode by incoherent broadband cavity enhanced absorption spectroscopy
