Abstract
Abstract. An incoherent broadband cavity-enhanced absorption spectroscopy (IBBCEAS) instrument for quantification of atmospheric trace gases that absorb in the cyan region of the electromagnetic spectrum (470 to 540 nm), including NO2 and I2, is described. The instrument uses a light-emitting diode coupled to a 1 m optical cavity consisting of a pair of mirrors in stable resonator configuration. Transmitted light is monitored using a grating spectrometer and charge-coupled device array detector. The average mirror reflectivity was determined from the N2∕He and Ar∕He ratios of scattering coefficients and was ∼99.98 % at its maximum, yielding an effective optical path length of 6.3 km. Cross sections of N2, O2, air, Ar, CO2, and CH4 scattering and of O4 absorption were measured and agree with literature values within the measurement uncertainty. Trace gas mixing ratios were retrieved using the spectral fitting software DOASIS (DOAS intelligent system) from 480 to 535 nm. Under laboratory conditions, the 60 s, 1σ measurement precisions were ±124 and ±44 pptv for NO2 and I2, respectively. The IBBCEAS instrument sampled ambient air in Ucluelet, BC, Canada, in July 2015. IBBCEAS retrievals agreed with independent measurements of NO2 by blue diode laser cavity ring-down spectroscopy (r2=0.975), but ambient I2 concentrations were below the detection limit.
Highlights
We describe an LED-powered incoherent broadband cavity-enhanced absorption spectroscopy (IBBCEAS) instrument operated in the cyan region of the electromagnetic spectrum
The IBBCEAS instrument consists of an LED light source, collimating optics, a high finesse optical cavity, focusing optics, specialized fibre bundle, and a spectrograph equipped with a charge-coupled device (CCD) camera (Fig. 2)
The IBBCEAS instrument was operated alongside the CRDS during a 4-week-long field intensive conducted at the Amphitrite Point Observatory (APO) on the west coast of Vancouver Island, British Columbia, Canada (Tokarek et al, 2017)
Summary
Cavity-enhanced absorption spectroscopy (CEAS) has emerged in recent years as a sensitive technique for direct measurement of atmospheric trace gases (Fiedler et al, 2003; Gherman et al, 2008; Vaughan et al, 2008; Washenfelder et al, 2008; Schuster et al, 2009; Thalman and Volkamer, 2010; Hoch et al, 2014) and of aerosol optical extinction (Thalman and Volkamer, 2010; Bluvshtein et al, 2012; Washenfelder et al, 2013). Prior laboratory measurements by Vaughan et al For this and other reasons (such as compactness and heat generation), light-emitting diodes (LEDs) are commonly used to generate broadband radiation (Washenfelder et al, 2008; Min et al, 2016). The potential of the instrument for quantification of iodine species in laboratory and field experiments is assessed
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