Development of an instrument for direct ozone production rate measurements: measurement reliability and current limitations

Abstract

Abstract. Ground-level ozone (O 3 ) is an important pollutant that affects both global climate change and regional air quality, with the latter linked to detrimental effects on both human health and ecosystems. Ozone is not directly emitted in the atmosphere but is formed from chemical reactions involving volatile organic compounds (VOCs), nitrogen oxides (NO x = NO + NO 2 ) and sunlight. The photochemical nature of ozone makes the implementation of reduction strategies challenging and a good understanding of its formation chemistry is fundamental in order to develop efficient strategies of ozone reduction from mitigation measures of primary VOCs and NO x emissions.An instrument for direct measurements of ozone production rates (OPRs) was developed and deployed in the field as part of the IRRONIC (Indiana Radical, Reactivity and Ozone Production Intercomparison) field campaign. The OPR instrument is based on the principle of the previously published MOPS instrument (Measurement of Ozone Production Sensor) but using a different sampling design made of quartz flow tubes and a different O x (O 3 and NO 2 ) conversiondetection scheme composed of an O 3 -to-NO 2 conversion unit and a cavity attenuated phase shift spectroscopy (CAPS) NO 2 monitor. Tests performed in the laboratory and in the field, together with model simulations of the radical chemistry occurring inside the flow tubes, were used to assess (i) the reliability of the measurement principle and (ii) potential biases associated with OPR measurements. This publication reports the first field measurements made using this instrument to illustrate its performance. The results showed that a photo-enhanced loss of ozone inside the sampling flow tubes disturbs the measurements. This issue needs to be solved to be able to perform accurate ambient measurements of ozone production rates with the instrument described in this study. However, an attempt was made to investigate the OPR sensitivity to NO x by adding NO inside the instrument. This type of investigations allows checking whether our understanding of the turnover point between NO x -limited and NO x -saturated regimes of ozone production is well understood and does not require measuring ambient OPR but instead only probing the change in ozone production when NO is added. During IRRONIC, changes in ozone production rates ranging from the limit of detection (3σ ) of 6.2 ppbv h −1 up to 20 ppbv h −1 were observed when 6 ppbv of NO was added into the flow tubes.

OH and HO<sub>2</sub> radical chemistry in a midlatitude forest: measurements and model comparisons

“…OH radicals are excited and detected using the A 2 + υ = 0 ← X 2 υ = 0 transition near 308 nm (Stevens et al, 1994). The net signal is measured by spectral modulation by tuning the wavelength on and off resonance in successive modulation cycles.…”

“…For example, RO 2 radicals produced from the OH-initiated oxidation of small alkanes were found to produce a negligible yield of HO 2 (Stevens et al, 1994;Kanaya et al, 2001;Tan, et al, 2001;Creasey et al, 2002;Holland et al, 2003). However, recent laboratory studies have shown that there are interferences associated with measurements of HO 2 from the conversion of RO 2 radicals derived from the OH-initiated oxidation of alkenes and aromatics to HO 2 (and subsequently OH) through the reaction with NO.…”

Mutual Information Input Selector and Probabilistic Machine Learning Utilisation for Air Pollution Proxies

“…As a result, the operational cost can be reduced and the number of monitoring stations can be scaled up. Finally, human involvement is typically required to operate some instruments, including "Ozone Analyzer" [57]. The O 3 proxy acts as a virtual sensor where the number of operators can be reduced.…”

OH and HO<sub>2</sub> radical chemistry in a midlatitude forest: Measurements and model comparisons

“…The IRRONIC campaign site was located within a mixed deciduous forest (sugar maple, sycamore, tulip polar, ash and hickory trees) at the Indiana University Research and Teaching Preserve (IU-RTP) field lab (39.1908º N, 86.502º W) located approximately 2.5 km northeast of the center of the Indiana University campus, and 1 km from the IN 45/46 bypass at the northern perimeter. The goals of the campaign included an informal intercomparison of peroxy radical measurements by two different techniques (Kundu et al, 2019), an analysis of ozone production sensitivity at this site (Sklaveniti et al, 2018), a https://doi.org/10.5194/acp-2019-726 Preprint. Discussion started: 21 August 2019 c Author(s) 2019.…”

“…Measurements were conducted on top of two scaffolding platforms adjacent to the field lab, approximately 1.8 m from the ground. Additional information regarding the field site and the IRRONIC campaign can be found in Sklaveniti et al (2018) and Kundu et al (2019). Table 1 summarizes the major instrumentation employed during the campaign.…”