Photonic Sensing of Reactive Atmospheric Species

Abstract

Chemically reactive short‐lived atmospheric species play a crucial role in tropospheric processes that affect regional air quality and global climate change. Contrary to long‐lived species (such as greenhouse gases), fast, interference‐free, accurate, and precise in situ monitoring of such strongly reactive species represents a real challenge owing to their very high reactivity resulting in short lifetimes (∼1–100 s) and ultralow concentrations (∼pptv). In this article, we give an overview of the recent progress in the development of absorption spectroscopy‐based photonic instruments involving modern photonic light sources (quantum cascade laser, distributed feedback diode laser, and light‐emitting diode) combined with high‐sensitivity spectroscopic measurement techniques such as incoherent broadband cavity‐enhanced absorption spectroscopy, Faraday rotation spectroscopy, wavelength‐modulation‐enhanced off‐axis integrated cavity output spectroscopy, tuning fork‐ or microphone‐based photoacoustic spectroscopy, and open‐path multipass absorption spectroscopy. Illustrative examples of monitoring some key atmospheric reactive species (such as HONO, OH, NO 3 , N 2 O 5 , and NO 2 ) will be presented for applications in intensive field campaigns, instrumented atmospheric simulation chamber, or laboratory investigation.

Laser gegen Luftverschmutzung

“…4. herrschte Smog. Die Nachweisgrenze des PA‐Systems beträgt 0,4 ppbv bei 1 min Zeitauflösung und 370 mW Laserleistung (aus ).…”

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

“…The accuracy of a measurement system reflects the closeness of a measured value to a true value, while the precision describes the degree to which repeated measurements under unchanged conditions show the same results (sometimes referred to as reproducibility or repeatability) [31]. In this work, the stability and precision of the BBCES instrument for CHOCHO and NO 2 were investigated using an Allan variance analysis.…”

“…To further improve the detection sensitivity and precision of the measured data, Kalman adaptive filtering [31,32,35] was applied in this work. As described in Refs [31] and [32], the 'true value' of the measurement at time k (ˆk δ ) can be predicted from the combination of the measured value at time k (z k ) and the previously determined 'true value' at time k-1 (ˆk δ − ) by using a recursive procedure, as expressed by following equation:…”

“…Signal averaging can improve the detection precision up to an optimum averaging time (as defined in Allan variance analysis [29]) but is ultimately limited by electrical and optical noise and short-term gas concentration variations. The Kalman filtering algorithm, developed by Kalman in 1960 [30], is one of the successful post-processing techniques that allows efficient on-line filtering of concentration measurements [31,32]. This technique was first applied in tunable diode laser absorption spectroscopy (TDLAS) by Werle et al [33]; it has since been extended to TDLAS based gas sensors [32,34] and real-time measurement of water isotopic ratios [35,36].…”

“…This technique was first applied in tunable diode laser absorption spectroscopy (TDLAS) by Werle et al [33]; it has since been extended to TDLAS based gas sensors [32,34] and real-time measurement of water isotopic ratios [35,36]. The Kalman filtering is computationally efficient, adaptive, and can adjust to changes in dynamic range during measurement without slowing the temporal response of the system [31,32]. This work presents the first time (to our knowledge) that Kalman filtering was applied in BBCES, for real-time optimization of the detection sensitivity and precision.…”