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A sensitive, compact detector for the simultaneous measurement of O3 and NO2 is presented in this work. There are two channels in the detector, namely the Ox channel and the NO2 channel. In the presence of excess NO, ambient O3 is converted to NO2 in the Ox measurement channel. In both channels, NO2 is directly detected via cavity ring-down spectroscopy (CRDS) at 409 nm. At a 10 s integration time, the Ox and NO2 channels have a 1σ precision of 14.5 and 13.5 pptv, respectively. The Allan deviation plot shows that the optimal sensitivity of O3 and NO2 occurs at an integration time of ~60 s, with values of 10.2 and 8.5 pptv, respectively. The accuracy is 6% for the O3 channel and 5% for the NO2 channel, and the largest uncertainty comes from the effective NO2 absorption cross-section. Intercomparison of the NO2 detection between the NO2 and Ox channels shows good agreement within their uncertainties, with an absolute shift of 0.31 ppbv, a correlation coefficient of R2 = 0.99 and a slope of 0.98. Further intercomparison for ambient O3 measurement between the O3/NO2-CRDS developed in this work and a commercial UV O3 monitor also shows excellent agreement, with linear regression slopes close to unity and an R2 value of 0.99 for 1 min averaged data. The system was deployed to measure O3 and NO2 concentrations in Hefei, China, and the observation results show obvious diurnal variation characteristics. The successful deployment of the system has demonstrated that the instrument can provide a new method for retrieving fast variations in ambient O3 and NO2. [ABSTRACT FROM AUTHOR]

A newly constructed thermal dissociation cavity ring-down spectrometer (TD-CRDS) for the simultaneous measurement of ambient total peroxy nitrates (ΣPNs, RO 2 NO 2), total alkyl nitrates (ΣANs, RONO 2), and NO 2 was presented in this work. ΣPNs and ΣANs were detected as NO 2 with the CRDS instrument after thermal dissociation. PNs and ANs completely dissociated at 180 °C and 360 °C, with conversion efficiencies of 96 % and 99 %, respectively. The effects of NO 2 and NO on measurement in different temperatures and two types of thermal dissociation inlet (TDI) were further explored. The influence of ambient NO 2 and NO on PNs and ANs in the improved TDI (TDI-2) was significantly improved. To further enhance the measurement accuracy, the consistency of the observed NO 2 in the three channels was tested, which achieved good agreement. The detection limits of the TD-CRDS instrument for NO 2 , ΣPNs, and ΣANs were determined as 6.5, 6.8, and 8.6 pptv (10 s, 1σ), respectively. Observations of PNs and ANs were conducted in a suburban site in Hefei, China, from September 2–30, 2021, using the TD-CRDS instrument, and the consecutive time series of PNs and ANs were derived, verifying the capability of the TD-CRDS instrument for continuous field observations of ΣPNs and ΣANs. [Display omitted] • A newly developed three-channel TD-CRDS instrument could simultaneously quantify ΣPNs, ΣANs, and NO 2. • The effects of NO 2 and NO on the measurements of PNs and ANs greatly ameliorated in the improved TDI. • The dissociation of PNs at 360 °C essentially did not affect the measurement of ANs. [ABSTRACT FROM AUTHOR]

Nitric oxide (NO) and nitrogen dioxide (NO2) are relevant to air quality due to their roles in tropospheric ozone (O3) production. In China, NOx emissions are very high and NOx emissions exhausted from on-road vehicles make up 20 % of total NOx emissions. In order to detect the NO and NO2 emissions on road, a dual-channel cavity ring-down spectroscopy (CRDS) system for NO2 and NO detection has been developed. In the system, NO is converted to NO2 by its reaction with excess O3 in the NOx channel, such that NO can be determined through the difference between two channels. The detection limits of NO2 and NOx for the system are estimated to be about 0.030 (1σ , 1 s) and 0.040 ppb (1 σ , 1 s), respectively. Considering the error sources of NO2 absorption cross section and RL determination, the total uncertainty of NO2 measurements is about 5%. The performance of the system was validated against a chemiluminescence (CL) analyser (42i, Thermo Scientific, Inc.) by measuring the NO2 standard mixtures. The measurement results of NO2 showed a linear correction factor (R2) of 0.99 in a slope of 1.031±0.006 , with an offset of (-0.940±0.323) ppb. An intercomparison between the system and a cavity-enhanced absorption spectroscopy (CEAS) instrument was also conducted separately for NO2 measurement in an ambient environment. Least-squares analysis showed that the slope and intercept of the regression line are 1.042±0.002 and (-0.393±0.040) ppb, respectively, with a linear correlation factor of R2=0.99. Another intercomparison conducted between the system and the CL analyser for NO detection also showed a good agreement within their uncertainties, with an absolute shift of (0.352±0.013) ppb, a slope of 0.957±0.007 and a correlation coefficient of R2=0.99. The system was deployed on the measurements of on-road vehicle emission plumes in Hefei, and the different emission characteristics were observed in the different areas of the city. The successful deployment of the system has demonstrated that the instrument can provide a new method for retrieving fast variations in NO and NO2 plumes. [ABSTRACT FROM AUTHOR]