Portable broadband cavity-enhanced spectrometer utilizing Kalman filtering: application to real-time, in situ monitoring of glyoxal and nitrogen dioxide

Abstract

This article describes the development and field application of a portable broadband cavity enhanced spectrometer (BBCES) operating in the spectral range of 440-480 nm for sensitive, real-time, in situ measurement of ambient glyoxal (CHOCHO) and nitrogen dioxide (NO). The instrument utilized a custom cage system in which the same SMA collimators were used in the transmitter and receiver units for coupling the LED light into the cavity and collecting the light transmitted through the cavity. This configuration realised a compact and stable optical system that could be easily aligned. The dimensions and mass of the optical layer were 676 × 74 × 86 mm and 4.5 kg, respectively. The cavity base length was about 42 cm. The mirror reflectivity at λ = 460 nm was determined to be 0.9998, giving an effective absorption pathlength of 2.26 km. The demonstrated measurement precisions (1σ) over 60 s were 28 and 50 pptv for CHOCHO and NO and the respective accuracies were 5% and 4%. By applying a Kalman adaptive filter to the retrieved concentrations, the measurement precisions of CHOCHO and NO were improved to 8 pptv and 40 pptv in 21 s.

Three-wavelength cavity-enhanced albedometer for measuring wavelength-dependent optical properties and single-scattering albedo of aerosols

“…The mirror reflectivity R(λ) was determined from the Rayleigh scattering of N 2 and CO 2 and the scaling factor (K') were determined from He, N 2 , CO 2 and SF 6 . More details about the procedure and reference cross sections can be found in [24] and [32] and references therein. R(λ) was determined to be 0.99960, 0.99970 and 0.99982 at 365, 532 and 660 nm, respectively.…”

“…The stability and precision of the CES-albedometer was investigated using an Allan variance analysis [32], as shown in Fig. 3.…”

“…The corresponding measurement precisions over 12 s (and 60 s) averaging times were 0.53 (0.28), 0.83 (0.44), and 0.93 (0.47) Mm −1 . The 3σ detection limit (LOD expected, 3σ ) of each parameter was determined from the Gaussian fitted frequency distribution of the time series measurement [32].…”

Development of an incoherent broadband cavity-enhanced absorption spectrometer for measurements of ambient glyoxal and NO<sub>2</sub> in a polluted urban environment

“…The limit of detection (LOD) can be defined as Eq. (5) from analytical chemistry and this method was also commonly used in cavityenhanced systems to evaluate instrument performance (Thalman et al, 2015;Fang et al, 2017).…”

Development of an incoherent broadband cavity-enhanced absorption spectrometer for measurements of ambient glyoxal and NO<sub>2</sub> in a polluted urban environment

“…It features high sensitivity, small chemical interference and simultaneous measurement of multiple components. IBBCEAS has been rapidly developed since Fiedler et al (2003) first described it in 2003. More recently, the technology has been successfully applied to measure a variety of trace gases (Min et al, 2016;Wang et al, 2017;Yi et al, 2016;Volkamer et al, 2015), weakly absorbed cross sections of different trace gases (Chen and Venables, 2011;Kahan et al, 2012) and aerosol extinction (Washenfelder et al, 2013).…”