Ultra-sensitive measurement of peroxy radicals by chemical amplification broadband cavity-enhanced spectroscopy

Abstract

The PERCA (PEroxy Radical Chemical Amplification) technique, which is based on the catalytic conversion of ambient peroxy radicals (HO and RO, where R stands for any organic chain) to a larger amount of nitrogen dioxide (NO) amplified by chain reactions by adding high concentrations of NO and CO in the flow reactor, has been widely used for total peroxy radical RO* (RO* = HO + ΣRO) measurements. High-sensitivity and accurate measurement of the NO concentration plays a key role in accurate measurement of the RO* concentration. In this paper, we report on the development of a dual-channel chemical amplification instrument, which combined the PERCA method with the incoherent broadband cavity-enhanced absorption spectroscopy (IBBCEAS), for peroxy radical measurements. The IBBCEAS method is capable of simultaneously measuring multiple species with high spectral identification, and can directly measure NO concentrations with high sensitivity and high accuracy and without interference from other absorbers. The detection sensitivity of the developed PERCA-IBBCEAS instrument for HO radicals was estimated to be about 0.9 pptv (1σ, 60 s) at a relative humidity (RH) of 10%. Considering the error sources of NO detection, CL determination, and the radical partitioning in the air sample, the total uncertainty of RO* measurements was about 16-20%.

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

“…Detection precisions for CHOCHO by BBCES instruments and other methods are compared in Table 1. A similar comparison of NO 2 measurement performance is given in Ref [27] for cavity-based instruments. The state-of-the-art performances of CHOCHO detection were achieved by Thalman and Volkamer [19] in 2010 and by Min et al [22] in 2016.…”

“…The reported 3σ detection precisions were 0.03 ppbv (60 s) with an L eff of 13 km and 0.045 ppbv (5 s) with an L eff of 17.8 km, respectively. The achievable sensitivity of BBCES depends on the number of photons injected into the cavity (which depends on the source brightness and beam imaging efficiency), L eff (which depends on the cavity mirror quality and mirror separation), and how efficiently the various noise components are suppressed [27,51]. In this work, the light injection efficiency was improved with the cage-based configuration.…”

“…These measurements are needed to investigate VOC degradation mechanisms and their impact on air quality through the production of O 3 and fine particles. While similar in some respects to our previously described BBCES instruments [24,26,27], the new BBCES instrument has been significantly improved by using a custom cage system and symmetrical transmitter and receiver units. These changes have improved both the instrument's physical specifications (reduced size and mass) and its performance characteristics (superior sensitivity and stability).…”

“…Compared to DOAS, which has a very long physical pathlength through the atmosphere, BBCES achieves comparable or superior sensitivity in a compact and robust system that is suited to mobile, high spatial resolution observations [17]. BBCES is also widely used for the measurement of other trace gases and atmospheric aerosol extinction [25][26][27][28], and references therein].…”

A new method for atmospheric detection of the CH<sub>3</sub>O<sub>2</sub> radical

“…One of the methods uses chemical ionisation mass spectrometry to determine the sum [HO 2 ] + i [RO 2,i ] or separately [HO 2 ], depending on the control of the flows of the NO and SO 2 reagents (Hanke et al, 2002;Edwards et al, 2003). The sum [HO 2 ] + i [RO 2,i ] has also been determined for many years by the peroxy radical chemical amplifier (PERCA) method, which uses NO and CO to generate NO 2 amplified by a chain reaction, and subsequently measured by a variety of methods, for example luminol fluorescence, laser-induced fluorescence (LIF) or cavity absorption methods (Cantrell and Stedman, 1982;Cantrell et al, 1984;Miyazaki et al, 2010;Hernandez et al, 2001;Green et al, 2006;Chen et al, 2016). A modification of PERCA, using a denuder to remove HO 2 has been used to estimate the sum of RO 2 (Miyazaki et al, 2010).…”