Broadband cavity-enhanced absorption spectroscopy in the ultraviolet spectral region for measurements of nitrogen dioxide and formaldehyde

Abstract

Abstract. Formaldehyde (CH 2 O) is the most abundant aldehyde in the atmosphere, and it strongly affects photochemistry through its photolysis. We describe simultaneous measurements of CH 2 O and nitrogen dioxide (NO 2 ) using broadband cavity-enhanced absorption spectroscopy in the ultraviolet spectral region. The light source consists of a continuous-wave diode laser focused into a Xenon bulb to produce a plasma that emits high-intensity, broadband light. The plasma discharge is optically filtered and coupled into a 1 m optical cavity. The reflectivity of the cavity mirrors is 0.99930 ± 0.00003 (1− reflectivity = 700 ppm loss) at 338 nm, as determined from the known Rayleigh scattering of He and zero air. This mirror reflectivity corresponds to an effective path length of 1.43 km within the 1 m cell. We measure the cavity output over the 315-350 nm spectral region using a grating monochromator and charge-coupled device array detector. We use published reference spectra with spectral fitting software to simultaneously retrieve CH 2 O and NO 2 concentrations. Independent measurements of NO 2 standard additions by broadband cavity-enhanced absorption spectroscopy and cavity ring-down spectroscopy agree within 2 % (slope for linear fit = 1.02 ± 0.03 with r 2 = 0.998). Standard additions of CH 2 O measured by broadband cavity-enhanced absorption spectroscopy and calculated based on flow dilution are also well correlated, with r 2 = 0.9998. During constant mixed additions of NO 2 and CH 2 O, the 30 s measurement precisions (1σ ) of the current configuration were 140 and 210 pptv, respectively. The current 1 min detection limit for extinction measurements at 315-350 nm provides sufficient sensitivity for measurement of trace gases in laboratory experiments and groundbased field experiments. Additionally, the instrument provides highly accurate, spectroscopically based trace gas detection that may complement higher precision techniques based on non-absolute detection methods. In addition to trace gases, this approach will be appropriate for measurements of aerosol extinction in ambient air, and this spectral region is important for characterizing the strong ultraviolet absorption by brown carbon aerosol.

Broadband optical properties of biomass‐burning aerosol and identification of brown carbon chromophores

“…The broadband cavity-enhanced spectrometer (BBCES) used in this study consists of two channels, one measured the aerosol optical extinction between 315 and 345 nm [Washenfelder et al, 2016] and the other between 390 and 420 nm [Washenfelder et al, 2013] (at 0.5 nm resolution). The same system was used and described in Bluvshtein et al [2016] The α ext (λ) of aerosol in BBCES is determined from the change in light intensity of the filled cavity relative to a particle-free cavity, taking into account the mirror reflectivity and the Rayleigh scattering of the carrier gas [Fiedler et al, 2003;Washenfelder et al, 2008].…”

Development of a portable cavity-enhanced absorption spectrometer for the measurement of ambient NO<sub>3</sub> and N<sub>2</sub>O<sub>5</sub>: experimental setup, lab characterizations, and field applications in a polluted urban environment

“…In previous work, R(λ) had been determined through four different methods, including the detection of a stable trace gas compound with known concentrations (Venables et al, 2006), the differentiation of pure gases with distinct Rayleigh scattering cross sections (Chen and Venables, 2011;Washenfelder et al, 2016;Min et al, 2016), the usage of low-loss optics (Varma et al, 2009), and the determination of the phase shift or ring down time (Langridge et al, 2008;Schuster et al, 2009;Kennedy et al, 2011). In this study, R(λ) is determined through the differentiation of pure gases (N 2 and He) in the cavity (Eq.…”

“…CRDS has high temporal and spatial resolution with high sensitivity and accuracy. Cavity-enhanced absorption spectroscopy (CEAS) was proposed later by Fiedler et al (2003) and has been successfully deployed to measure a number of atmospheric trace gas compounds like HONO, H 2 O, IO, O 3 , O 4 , I 2 , IO, OIO, SO 2 , NO 3 , N 2 O 5 , glyoxal (CHOCHO), and methylgloxal (CH 3 COCHO; Washenfelder et al, 2008Washenfelder et al, , 2013Washenfelder et al, , 2016Thalman and Volkamer, 2010;Gherman et al, 2008;Axson et al, 2011;Kahan et al, 2012;Min et al, 2016). The measurement of NO 3 was shown to be successful in simulation chamber conditions with an open-path incoherent broadband CEAS setup (Venables et al, 2006;Varma et al, 2009), and shortly afterwards, the closed cavity type of IBBCEAS was successfully deployed on the ground (Langridge et al, 2008;Benton et al, 2010) and airborne (Kennedy et al, 2011) for measurements of both NO 3 and N 2 O 5 .…”

A new non-resonant laser-induced fluorescence instrument for the airborne in situ measurement of formaldehyde

“…Atmospheric HCHO is measured using a variety of airborne instrumental methods, including mass spectrometry (Warneke et al, 2011), wet chemistry (Aiello and McLaren, J. M. St. Clair et al: A new non-resonant laser-induced fluorescence instrument 2009; Junkermann and Burger, 2006;Lazrus et al, 1988), absorption spectroscopy (Baidar et al, 2013;Catoire et al, 2012;Richter et al, 2015;Washenfelder et al, 2016;Weibring et al, 2006;Yokelson et al, 1999), and laser-induced fluorescence (LIF) (Cazorla et al, 2015;Hottle et al, 2009;Mohlmann, 1985). In addition to airborne observations, total column HCHO is measured by satellite (Chance et al, 2000;Steck et al, 2008), making HCHO one of the few VOCs observable from space.…”