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1. Simultaneous detection of ozone and nitrogen dioxide by oxygen anion chemical ionization mass spectrometry: a fast-time-response sensor suitable for eddy covariance measurements

   https://doi.org/10.5194/amt-13-1887-2020  

   Novak, Gordon A.; Vermeuel, Michael P.; Bertram, Timothy H. (January 2020, Atmospheric Measurement Techniques)

   Abstract. We report on the development, characterization, and fielddeployment of a fast-time-response sensor for measuring ozone (O3) andnitrogen dioxide (NO2) concentrations utilizing chemical ionizationtime-of-flight mass spectrometry (CI-ToFMS) with oxygen anion(O2-) reagent ion chemistry. Wedemonstrate that the oxygen anion chemical ionization mass spectrometer(Ox-CIMS) is highly sensitive to both O3 (180 counts s−1 pptv−1) and NO2 (97 counts s−1 pptv−1), corresponding todetection limits (3σ, 1 s averages) of 13 and 9.9 pptv,respectively. In both cases, the detection threshold is limited by themagnitude and variability in the background determination. The short-termprecision (1 s averages) is better than 0.3 % at 10 ppbv O3 and 4 %at 10 pptv NO2. We demonstrate that the sensitivity of the O3measurement to fluctuations in ambient water vapor and carbon dioxide isnegligible for typical conditions encountered in the troposphere. Theapplication of the Ox-CIMS to the measurement of O3 vertical fluxesover the coastal ocean, via eddy covariance (EC), was tested during the summer of2018 at Scripps Pier, La Jolla, CA. The observed mean ozone depositionvelocity (vd(O3)) was 0.013 cm s−1 with a campaign ensemblelimit of detection (LOD) of 0.0027 cm s−1 at the 95 % confidencelevel, from each 27 min sampling period LOD. The campaign mean and 1standard deviation range of O3 mixing ratios was 41.2±10.1 ppbv. Several fast ozone titration events from local NO emissions weresampled where unit conversion of O3 to NO2 was observed,highlighting instrument utility as a total odd-oxygen (Ox=O3+NO2) sensor. The demonstrated precision, sensitivity, and timeresolution of this instrument highlight its potential for directmeasurements of O3 ocean–atmosphere and biosphere–atmosphere exchangefrom both stationary and mobile sampling platforms. 

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2. Ozone deposition to a coastal sea: comparison of eddy covariance observations with reactive air–sea exchange models

   https://doi.org/10.5194/amt-13-6915-2020  

   Loades, David C.; Yang, Mingxi; Bell, Thomas G.; Vaughan, Adam R.; Pound, Ryan J.; Metzger, Stefan; Lee, James D.; Carpenter, Lucy J. (January 2020, Atmospheric Measurement Techniques)

   null (Ed.)

   Abstract. A fast-response (10 Hz) chemiluminescence detector forozone (O3) was used to determine O3 fluxes using the eddy covariancetechnique at the Penlee Point Atmospheric Observatory (PPAO) on the southcoast of the UK during April and May 2018. The median O3 flux was −0.132 mg m−2 h−1 (0.018 ppbv m s−1),corresponding to a deposition velocity of 0.037 cm s−1(interquartile range 0.017–0.065 cm s−1) – similar to thehigher values previously reported for open-ocean flux measurements but notas high as some other coastal results. We demonstrate that a typical singleflux observation was above the 2σ limit of detection but hadconsiderable uncertainty. The median 2σ uncertainty of depositionvelocity was 0.031 cm s−1 for each 20 min period, whichreduces with the square root of the sample size. Eddy covariance footprintanalysis of the site indicates that the flux footprint was predominantlyover water (> 96 %), varying with atmospheric stability and, toa lesser extent, with the tide. At very low wind speeds when the atmospherewas typically unstable, the observed ozone deposition velocity was elevated,most likely because the footprint contracted to include a greater landcontribution in these conditions. At moderate to high wind speeds whenatmospheric stability was near-neutral, the ozone deposition velocityincreased with wind speed and showed a linear dependence with frictionvelocity. This observed dependence on friction velocity (and therefore alsowind speed) is consistent with the predictions from the one-layer model ofFairall et al. (2007), which parameterisesthe oceanic deposition of ozone from the fundamental conservation equation,accounting for both ocean turbulence and near-surface chemical destruction,while assuming that chemical O3 destruction by iodide is distributed overdepth. In contrast to our observations, the deposition velocity predicted bythe recently developed two-layer model of Luhar et al. (2018) (whichconsiders iodide reactivity in both layers but with molecular diffusivitydominating over turbulent diffusivity in the first layer) shows no majordependence of deposition velocity on wind speed and underestimates themeasured deposition velocities. These results call for further investigationinto the mechanisms and control of oceanic O3 deposition. 

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3. Ozone depletion due to dust release of iodine in the free troposphere

   https://doi.org/10.1126/sciadv.abj6544  

   Koenig, Theodore K.; Volkamer, Rainer; Apel, Eric C.; Bresch, James F.; Cuevas, Carlos A.; Dix, Barbara; Eloranta, Edwin W.; Fernandez, Rafael P.; Hall, Samuel R.; Hornbrook, Rebecca S.; et al (December 2021, Science Advances)

   Iodine is an atmospheric trace element emitted from oceans that efficiently destroys ozone (O 3 ). Low O 3 in airborne dust layers is frequently observed but poorly understood. We show that dust is a source of gas-phase iodine, indicated by aircraft observations of iodine monoxide (IO) radicals inside lofted dust layers from the Atacama and Sechura Deserts that are up to a factor of 10 enhanced over background. Gas-phase iodine photochemistry, commensurate with observed IO, is needed to explain the low O 3 inside these dust layers (below 15 ppbv; up to 75% depleted). The added dust iodine can explain decreases in O 3 of 8% regionally and affects surface air quality. Our data suggest that iodate reduction to form volatile iodine species is a missing process in the geochemical iodine cycle and presents an unrecognized aeolian source of iodine. Atmospheric iodine has tripled since 1950 and affects ozone layer recovery and particle formation. 

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4. Iodine chemistry in the chemistry–climate model SOCOL-AERv2-I

   https://doi.org/10.5194/gmd-14-6623-2021  

   Karagodin-Doyennel, Arseniy; Rozanov, Eugene; Sukhodolov, Timofei; Egorova, Tatiana; Saiz-Lopez, Alfonso; Cuevas, Carlos A.; Fernandez, Rafael P.; Sherwen, Tomás; Volkamer, Rainer; Koenig, Theodore K.; et al (January 2021, Geoscientific Model Development)

   Abstract. In this paper, we present a new version of the chemistry–climate model SOCOL-AERv2 supplemented by an iodine chemistry module. We perform three 20-year ensemble experiments to assess the validity of the modeled iodine and to quantify the effects of iodine on ozone. The iodine distributions obtained with SOCOL-AERv2-I agree well with AMAX-DOAS observations and with CAM-chem model simulations. For the present-day atmosphere, the model suggests that the iodine-induced chemistry leads to a 3 %–4 % reduction in the ozone column, which is greatest at high latitudes. The model indicates the strongest influence of iodine in the lower stratosphere with 30 ppbv less ozone at low latitudes and up to 100 ppbv less at high latitudes. In the troposphere, the account of the iodine chemistry reduces the tropospheric ozone concentration by 5 %–10 % depending on geographical location. In the lower troposphere, 75 % of the modeled ozone reduction originates from inorganic sources of iodine, 25 % from organic sources of iodine. At 50 hPa, the results show that the impacts of iodine from both sources are comparable. Finally, we determine the sensitivity of ozone to iodine by applying a 2-fold increase in iodine emissions, as it might be representative for iodine by the end of this century. This reduces the ozone column globally by an additional 1.5 %–2.5 %. Our results demonstrate the sensitivity of atmospheric ozone to iodine chemistry for present and future conditions, but uncertainties remain high due to the paucity of observational data of iodine species. 

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5. Impacts of meteorology and emissions on summertime surface ozone increases over central eastern China between 2003 and 2015

   https://doi.org/10.5194/acp-19-1455-2019  

   Sun, Lei; Xue, Likun; Wang, Yuhang; Li, Longlei; Lin, Jintai; Ni, Ruijing; Yan, Yingying; Chen, Lulu; Li, Juan; Zhang, Qingzhu; et al (January 2019, Atmospheric Chemistry and Physics)

   Abstract. Recent studies have shown that surface ozone (O3)concentrations over central eastern China (CEC) have increased significantlyduring the past decade. We quantified the effects of changes inmeteorological conditions and O3 precursor emissions on surface O3levels over CEC between July 2003 and July 2015 using the GEOS-Chem model.The simulated monthly mean maximum daily 8 h average O3 concentration(MDA8 O3) in July increased by approximately 13.6 %, from 65.5±7.9 ppbv (2003) to 74.4±8.7 ppbv (2015), comparable to the observedresults. The change in meteorology led to an increase in MDA8 O3 of5.8±3.9 ppbv over the central part of CEC, in contrast to a decreaseof about -0.8±3.5 ppbv over the eastern part of the region. Incomparison, the MDA8 O3 over the central and eastern parts of CECincreased by 3.5±1.4 and 5.6±1.8 ppbv due to the increasedemissions. The increase in averaged O3 in the CEC region resulting fromthe emission increase (4.0±1.9 ppbv) was higher than that caused bymeteorological changes (3.1±4.9 ppbv) relative to the 2003 standardsimulation, while the regions with larger O3 increases showed a highersensitivity to meteorological conditions than to emission changes.Sensitivity tests indicate that increased levels of anthropogenic non-methanevolatile organic compounds (NMVOCs) dominate the O3 increase over theeastern part of CEC, and anthropogenic nitrogen oxides (NOx) mainly increaseMDA8 O3 over the central and western parts and decrease O3 in afew urban areas in the eastern part. Budget analysis showed that netphotochemical production and meteorological conditions (transport inparticular) are two important factors that influence O3 levels over theCEC. The results of this study suggest a need to further assess theeffectiveness of control strategies for O3 pollution in the context ofregional meteorology and anthropogenic emission changes. 

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