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Gaseous hydrochloric (HCl) and hydrobromic acid (HBr) are vital halogen species that play essential roles in tropospheric physicochemical processes. Yet, the majority of the current studies on these halogen species were conducted in marine or coastal areas. Detection and source identification of HCl and HBr in inland urban areas remain scarce, thus limiting the full understanding of halogen chemistry and potential atmospheric impacts in the environments with limited influence from the marine sources. Here, both gaseous HCl and HBr were concurrently measured in urban Beijing, China, during winter and early spring of 2019. We observed significant HCl and HBr concentrations ranging from a minimum value at 1 × 108 molecules cm−3 (4 ppt) and 4 × 107 molecules cm−3 (1 ppt) up to 6 × 109 molecules cm−3 (222 ppt) and 1 × 109 molecules cm−3 (37 ppt), respectively. The HCl and HBr concentrations are enhanced along with the increase of atmospheric temperature, UVB and levels of gaseous HNO3. Based on the air mass analysis and high correlations of HCl and HBr with the burning indicators (HCN and HCNO), gaseous HCl and HBr are found to be related to anthropogenic burning aerosols. The gas–particle partitioning may also play a dominant role in the elevated daytime HCl and HBr. During the daytime, the reactions of HCl and HBr with OH radicals lead to significant production of atomic Cl and Br, up to 2 × 104 molecules cm−3 s−1 and 8 × 104 molecules cm−3 s−1, respectively. The production rate of atomic Br (via HBr + OH) is 2–3 times higher than that of atomic Cl (via HCl + OH), highlighting the potential importance of bromine chemistry in the urban area. On polluted days, the production rates of atomic Cl and Br are faster than those on clean days. Furthermore, our observations of elevated HCl and HBr may suggest an important recycling pathway of halogen species in inland megacities and may provide a plausible explanation for the widespread halogen chemistry, which could affect the atmospheric oxidation in China.

Measuring concentrations of trace species that may have a significant impact on health, climate or the stability of the ozone layer, is a serious challenge. Future space missions, planned at high sensitivity, will bring progress if and only if the necessary spectral parameters are available. For some species of atmospheric interest such as nitryl chloride (ClNO₂), phosgene (Cl₂CO) and chlorine nitrate (ClONO₂), spectroscopic data are incomplete or almost non-existent. The challenge in this thesis is to get spectroscopic parameters (line positions and intensities or absorption cross sections) for these species in support of atmospheric applications. However, apart from Cl₂CO, spectroscopy of ClNO₂ and ClONO₂ is made difficult by their very complicated chemical synthesis, their reactivity with metals and organic materials, and their instability in the presence of light and heat. Moreover, these molecules are quite heavy (presence of chlorine with its two isotopomers) and exhibit dense spectra that are quite complicated by numerous perturbations affecting vibration-rotation levels.In the case of ClNO₂, spectra were recorded in the range 300 – 900 cm-1 with much improved experimental conditions (high resolution, low temperature, long path, low pressure) using the synchrotron radiation of the AILES beamline at SOLEIL. Precise modelling of the 370 and 790 cm-1 regions has been performed. These regions could be used for a future atmospheric remote sensing by FTIR spectroscopy respectively by FORUM and IASI-NG instruments. The low energy vibrations of ClONO₂ that have been never observed at high resolution before this work were also measured. A first modelling of the torsional region around 120 cm-1 is presented in this thesis. The analysis of these vibrations will be useful for the modelling of hot bands in the atmospheric windows where ClONO₂ is currently detected, and in fine will lead to a much more precise retrieval of the ClONO₂ concentration profile. Regarding Cl₂CO, cross sections have been measured at LISA, on one hand, at room temperature to compare data with previous works and, on the other, in stratospheric conditions to support satellite remote sensing applications., La mesure des concentrations d’espèces à l’état de trace, susceptibles d’avoir un impact notable sur la santé, le climat ou la stabilité de la couche d’ozone constitue un véritable défi. Les prochaines missions spatiales, prévues à haute sensibilité, apporteront un progrès si et seulement si les paramètres spectraux nécessaires sont disponibles. Pour certaines espèces d’intérêt atmosphérique telles que le chlorure de nitryle (ClNO₂), le phosgène (Cl₂CO) et le nitrate de chlore (ClONO₂), les données spectroscopiques sont incomplètes ou quasiment inexistantes. Le défi dans cette thèse consiste à obtenir des paramètres spectroscopiques (positions et intensités de raies ou sections efficaces d’absorption) pour ces espèces, en vue des applications atmosphériques. Cependant, hormis Cl₂CO, la spectroscopie de ClNO₂₂ et ClONO₂ est rendue difficile par leur synthèse chimique très complexe, leur réactivité avec les métaux et les matériaux organiques et leur instabilité en présence de lumière et chaleur. De plus, ces molécules sont assez lourdes (présence du chlore avec ses deux isotopomères) et présentent des spectres denses et assez compliqués par de nombreuses perturbations qui affectent les niveaux de vibration-rotation.Dans le cas de ClNO₂, des spectres ont été enregistrés dans la gamme 300 – 900 cm-1 avec de meilleures conditions expérimentales (haute résolution, basse température, long parcours, faible pression) en utilisant le rayonnement synchrotron de la ligne AILES à SOLEIL. Des modélisations précises des régions à 370 et 790 cm-1 ont été effectuées. Ces régions pourront être exploitées pour une future télédétection atmosphérique par spectroscopie IRTF respectivement par les instruments FORUM et IASI-NG. Les vibrations de basse énergie de ClONO₂ jamais observées à haute résolution avant ce travail ont également été mesurées. Une première modélisation de la région de la torsion vers 120 cm-1 est présentée dans cette thèse. L’analyse de ces vibrations sera utile pour modéliser les bandes chaudes dans les fenêtres atmosphériques où ClONO₂ est actuellement détecté, et in fine permettra d’aboutir à une restitution bien plus précise du profil de concentration de ClONO₂. Concernant Cl₂CO, des sections efficaces ont été mesurées au LISA, d’une part, à température ambiante pour clarifier les données des travaux antérieurs et, d’autre part, dans les conditions stratosphériques en soutien à la télédétection satellitaire.

Production of hydroxyl (OH) radicals is frequently dominated by the photolysis of tropospheric ozone (O3). However, photolysis of nocturnal radical reservoirs, such as nitrous acid (HONO) and nitryl chloride (ClNO2), also produces radicals (OH and Cl atoms) that contribute to the oxidising capacity of the local atmosphere, and initiate many radical-chain reactions that lead to the formation of harmful secondary pollutants. Photolysis of nitric acid (HNO3) is also a minor radical production mechanism. In this paper, locally representative photolysis rate constants (j-values) for these molecules are shown to be critical for quantifying and understanding the rate of radical production in a local atmosphere. The first long-term 4-π filter radiometer dataset in the UK (21 November 2018–20 November 2019) available for direct atmospheric model validation is reported. Measurements were made at Auchencorth Moss, a Scottish rural background site, and j(NO2) is used to generate a measurement-driven adjustment factor (MDAF) for calculated j-values that accounts for local changes in meteorological variables without significantly increasing computational cost. Modelled clear-sky j-values and actinic flux for Auchencorth Moss were generated using the Tropospheric Ultraviolet and Visible radiation model (TUV; v.5.3.1). Applying the MDAF metric resulted in the calculated photolytic production rate of OH radicals, from all sources considered, being ~40 % lower over the year. Photolysis of HONO resulted in an increased rate of OH production compared to that from O3 in low-light conditions, such as sunrise and sunset (Solar Zenith Angle > 80°). Hydroxyl radical production from HONO photolysis exceeded that from O3 consistently throughout the day during the winter and autumn (by a factor of 5 and 2.1, respectively). Radical production rates from HONO and ClNO2 reached maximum values during the early morning hours of summer (06:00–09:00 UTC), with OH produced at a rate of 1.06 × 106 OH radicals cm−3 s−1, and Cl radicals at 3.20 × 104 Cl radicals cm−3 s−1, with the MDAF metric applied. This first application of the MDAF j-values demonstrates an efficient measurement and computational approach to improve modelling of the local atmospheric photochemistry that drives NO2, O3 and PM pollution levels. The incorporation of local radiation measurements in measurement networks, and the consequent greater spatial resolution of locally-relevant photolysis coefficients in model photolysis parameterisations, will improve the accuracy of assessment of air pollution and policy-intervention impacts.

Measuring concentrations of trace species that may have a significant impact on health, climate or the stability of the ozone layer, is a serious challenge. Future space missions, planned at high sensitivity, will bring progress if and only if the necessary spectral parameters are available. For some species of atmospheric interest such as nitryl chloride (ClNO2), phosgene (Cl2CO) and chlorine nitrate (ClONO2), spectroscopic data are incomplete or almost non-existent. The challenge in this thesis is to get spectroscopic parameters (line positions and intensities or absorption cross sections) for these species in support of atmospheric applications. However, apart from Cl2CO, spectroscopy of ClNO2 and ClONO2 is made difficult by their very complicated chemical synthesis, their reactivity with metals and organic materials, and their instability in the presence of light and heat. Moreover, these molecules are quite heavy (presence of chlorine with its two isotopomers) and exhibit dense spectra that are quite complicated by numerous perturbations affecting vibration-rotation levels.In the case of ClNO2, spectra were recorded in the range 300 – 900 cm-1 with much improved experimental conditions (high resolution, low temperature, long path, low pressure) using the synchrotron radiation of the AILES beamline at SOLEIL. Precise modelling of the 370 and 790 cm-1 regions has been performed. These regions could be used for a future atmospheric remote sensing by FTIR spectroscopy respectively by FORUM and IASI-NG instruments. The low energy vibrations of ClONO2 that have been never observed at high resolution before this work were also measured. A first modelling of the torsional region around 120 cm-1 is presented in this thesis. The analysis of these vibrations will be useful for the modelling of hot bands in the atmospheric windows where ClONO2 is currently detected, and in fine will lead to a much more precise retrieval of the ClONO2 concentration profile. Regarding Cl2CO, cross sections have been measured at LISA, on one hand, at room temperature to compare data with previous works and, on the other, in stratospheric conditions to support satellite remote sensing applications., La mesure des concentrations d’espèces à l’état de trace, susceptibles d’avoir un impact notable sur la santé, le climat ou la stabilité de la couche d’ozone constitue un véritable défi. Les prochaines missions spatiales, prévues à haute sensibilité, apporteront un progrès si et seulement si les paramètres spectraux nécessaires sont disponibles. Pour certaines espèces d’intérêt atmosphérique telles que le chlorure de nitryle (ClNO2), le phosgène (Cl2CO) et le nitrate de chlore (ClONO2), les données spectroscopiques sont incomplètes ou quasiment inexistantes. Le défi dans cette thèse consiste à obtenir des paramètres spectroscopiques (positions et intensités de raies ou sections efficaces d’absorption) pour ces espèces, en vue des applications atmosphériques. Cependant, hormis Cl2CO, la spectroscopie de ClNO2 et ClONO2 est rendue difficile par leur synthèse chimique très complexe, leur réactivité avec les métaux et les matériaux organiques et leur instabilité en présence de lumière et chaleur. De plus, ces molécules sont assez lourdes (présence du chlore avec ses deux isotopomères) et présentent des spectres denses et assez compliqués par de nombreuses perturbations qui affectent les niveaux de vibration-rotation.Dans le cas de ClNO2, des spectres ont été enregistrés dans la gamme 300 – 900 cm-1 avec de meilleures conditions expérimentales (haute résolution, basse température, long parcours, faible pression) en utilisant le rayonnement synchrotron de la ligne AILES à SOLEIL. Des modélisations précises des régions à 370 et 790 cm-1 ont été effectuées. Ces régions pourront être exploitées pour une future télédétection atmosphérique par spectroscopie IRTF respectivement par les instruments FORUM et IASI-NG. Les vibrations de basse énergie de ClONO2 jamais observées à haute résolution avant ce travail ont également été mesurées. Une première modélisation de la région de la torsion vers 120 cm-1 est présentée dans cette thèse. L’analyse de ces vibrations sera utile pour modéliser les bandes chaudes dans les fenêtres atmosphériques où ClONO2 est actuellement détecté, et in fine permettra d’aboutir à une restitution bien plus précise du profil de concentration de ClONO2. Concernant Cl2CO, des sections efficaces ont été mesurées au LISA, d’une part, à température ambiante pour clarifier les données des travaux antérieurs et, d’autre part, dans les conditions stratosphériques en soutien à la télédétection satellitaire.

Nitrate radical (NO3) and dinitrogen pentoxide (N2O5) play crucial roles in the nocturnal atmosphere. To quantify their impacts, we deployed a thermal-dissociation chemical ionization mass spectrometry (TD-CIMS), to measure their concentration, as well as ClNO2 at a coastal background site in the southern of China during the late autumn of 2012. Moderate levels of NO3, N2O5 and high concentration of ClNO2 were observed during the study period, indicating active NOx-O-3 chemistry in the region. Distinct features of NO3, N2O5 and ClNO2 mixing ratios were observed in different airmasses. Further analysis revealed that the N2O5 heterogeneous reaction was the dominant loss of N2O5 and NO3, which showed higher loss rate compared to that in other coastal sites. Especially, the N2O5 loss rates could reach up to 0.0139 s(-1) when airmasses went across the sea. The fast heterogeneous loss of N2O5 led to rapid NOx loss which could be comparable to the daytime process through NO2 oxidization by OH, and on the other hand, to rapid nitrate aerosol formation. In summary, our results revealed that the N2O5 hydrolysis could play significant roles in regulating the air quality by reducing NOx but forming nitrate aerosols. (C) 2019 Published by Elsevier B.V.

International audience; A new investigation of the ν3 bands of 35ClNO2 and 37 ClNO2, located around 370 cm−1 has been performed using a high resolution (0.00102 cm−1) Fourier transform spectrum recorded at SOLEIL with highly improved experimental conditions as compared to previous work [Orphal J, Morillon-Chapey M, Klee S, Mellau GC, Winnewisser M. J Mol Spectrosc 1998;190:101–6]: (i) the use of synchrotron radiation which resulted in a better signal-to-noise ratio; (ii) a resolution twice better; (iii) a low temperature (221 K) with an optical path length of 8.16 m, allowing low pressure (0.025 hPa) in the sample leading to a well resolved spectrum. As a consequence, significantly better results than previously were obtained. Thanks to the new experimental conditions, the line assignments were pursued up to higher J and Ka quantum number values, J = 83 and Ka = 44. For both isotopomers, a total of 6331 transitions were reproduced with a root-mean-square deviation of 2 × 10−4 cm−1 using a Watson-type A-reduced Hamiltonian. Improved rotational and centrifugal distortion constants for the ν3 fundamental bands of 35ClNO2 and 37 ClNO2 have been determined. The band centers are 370.1510773(92) cm−1 for the ν3 fundamental band of 35ClNO2 and 364.5218094(96) cm−1 for the ν3 fundamental band of 37ClNO2. The synthetic line list obtained in this study could be interesting for future measurements of ClNO2 in the atmosphere, e.g. using the new space mission FORUM which is one of the concepts chosen by ESA to be developed further and which opens up a new window (150–1400 cm−1 ) for understanding and quantifying the radiative processes, as well as air quality and pollution effects

The oxidation of primary emitted species such as volatile organic compounds (VOCs) acts as a source of ozone and therefore has detrimental effects on air quality and climate. In order to understand at what rate oxidation is occurring in the troposphere, i.e. the oxidation capacity, an understanding of the contributors to oxidation and possible markers of oxidation are imperative. Formic acid, a ubiquitous trace gas, which contributes significantly to the acidity of precipitation, could, because of its dominant source being suggested to be the ozonolysis of alkenes, be used as a marker for oxidation. A chemical ionisation mass spectrometer (CIMS) with a quadruple mass analyser utilising the I ionisation scheme was therefore deployed in London during both the summer and winter Clean Air for London (ClearfLO) Campaign to measure formic acid in order to asses this possibility. Simultaneous formic and nitric acid measurements with the CIMS, as well as supplementary gas phase data, in the winter ClearfLO campaign indicated the dominance of direct anthropogenic emissions of formic acid at this time and location. Global modelling simulations including a direct anthropogenic emission of formic acid suggested that this source is responsible for up to 30% of total formic acid in certain regions of the northern hemisphere, an area where this acid is most significantly underestimated. This ruled out the possibility of using formic acid as a marker for oxidation as a result of its vast range of sources. The mirrored summer campaign, also simultaneously detecting formic acid and nitric acid, showed that secondary photochemical production was, however, a dominant source in this time and location. The first UK measurements of ClNO2 are reported here – which is a region where modelling studies predict significant ClNO2 production all year round. Concentrations of ClNO2 up to 724 ppt and a mean of 207 ppt were measured in London during the summer ClearfLO campaign. Cl atoms from ClNO2 photolysis were shown to contribute up to 15%, 3% and 26% of the oxidation of alkanes, alkenes and alkynes, respectively over the full day. This will increase the tropospheric ozone forming potential at this time, particularly in the early morning.As well as very limited ClNO2 measurements in Europe, measurements from low NOx sites and airborne measurements are also highly understudied. Measurements of ClNO2 in the rural coastal site of Weybourne and an altitude profile from the FAAM Bae-146 Research aircraft were therefore undertaken. Concentrations of ClNO2 were significantly lower in Weybourne in comparison to the London study with peaks of 80 ppt with night-time average of 15 ppt being observed. The importance of Cl atoms to VOC oxidation at this site was much reduced in comparison to London owing to the higher OH concentrations and lower production of ClNO2 at this site.

The first nitryl chloride (ClNO2) measurements in the UK were made during the summer 2012 ClearfLo campaign with a chemical ionization mass spectrometer, utilizing an I− ionization scheme. Concentrations of ClNO2 exceeded detectable limits (11 ppt) every night with a maximum concentration of 724 ppt. A diurnal profile of ClNO2 peaking between 4 and 5 A.M., decreasing directly after sunrise, was observed. Concentrations of ClNO2 above the detection limit are generally observed between 8 P.M. and 11 A.M. Different ratios of the production of ClNO2:N2O5 were observed throughout with both positive and negative correlations between the two species being reported. The photolysis of ClNO2 and a box model utilizing the Master Chemical Mechanism modified to include chlorine chemistry was used to calculate Cl atom concentrations. Simultaneous measurements of hydroxyl radicals (OH) using low pressure laser-induced fluorescence and ozone enabled the relative importance of the oxidation of three groups of measured VOCs (alkanes, alkenes, and alkynes) by OH radicals, Cl atoms, and O3 to be compared. For the day with the maximum calculated Cl atom concentration, Cl atoms in the early morning were the dominant oxidant for alkanes and, over the entire day, contributed 15%, 3%, and 26% toward the oxidation of alkanes, alkenes, and alkynes, respectively.

WOS:000324032900041 Nitryl chloride (ClNO2) is a chlorine atom source and reactive nitrogen reservoir formed during the night by heterogeneous reactions of dinitrogen pentoxide on chloride-containing aerosol particles. The main factors that influence ClNO2 production include nitrogen oxides, ozone, aerosol surface area, soluble chloride, and ambient relative humidity. Regions with strong anthropogenic activity therefore have large ClNO2 formation potential even inland of coastal regions due to transport or local emissions of soluble chloride. As part of the Nitrogen, Aerosol Composition, and Halogens on a Tall Tower field study, we report wintertime vertically resolved ClNO2 and molecular chlorine (Cl-2) measurements taken on a 300 m tall tower located at NOAA's Boulder Atmospheric Observatory in Weld County, CO, during February and March of 2011. Gas and particle phase measurements aboard the tower carriage allowed for a detailed description of the chemical state of the nocturnal atmosphere as a function of height. These observations show significant vertical structure in ClNO2 and Cl-2 mixing ratios that undergo dynamic changes over the course of a night. Using these measurements, we focus on two distinct combustion plume events where ClNO2 mixing ratios reached 600 and 1300 parts per trillion by volume, respectively, aloft of the nocturnal surface layer. We infer ClNO2 yields from N2O5-aerosol reactions using both observational constraints and box modeling. The derived yields in these plumes suggest efficient ClNO2 production compared to the campaign average, where in-plume yields range from 0.3 to 1; the campaign average yield in the boundary layer is 0.05 +/- 0.15, with substantial night-to-night and within night variability similar to previous measurements in this region.

A comparative study of isomers and conformers of halogen nitrites, XONO (X = Cl, Br, I), with particular emphasis on the I derivatives, has been carried out using high levels of electronic structure theory. All isomeric and conformeric structures and cis- to trans-conformational barriers were determined for each family. The nitryl halide isomers, XNO2, were calculated to be the lowest energy compounds. Interesting variations in the structural parameters, harmonic vibrational frequencies and stabilization energies were obtained on halogen substitution, that are particularly pronounced in the iodine family. Molecular Physics

The reaction IO + NO -> I + NO2 has been studied theoretically using DFT and ab initio methods. Six transition state configurations have been characterized in total. Four of them correspond to the conformational and isomerization barriers among the reaction intermediates, namely between cis-and trans-iodine nitrites, IONOc, IONOt and nitryl iodide, INO2. Interesting features identified in the potential energy surface are the two distinct iodine abstraction transition states that lead to I + NO2 through each nitrite conformer. The heats of formation for the three bound intermediates are evaluated based on the calculated dissociation energies and are compared to the corresponding properties of the Cl and Br derivatives. (c) 2006 Elsevier B.V. All rights reserved. Chemical Physics Letters