AS3.12

Iodine chemistry is a driver of new particle formation in the marine and polar boundary layer, with potential influence on cloud formation and properties. There are however conflicting views about how iodine gas-to-particle conversion proceeds. Laboratory studies indicate that iodine photooxidation yields iodine oxides, which are well-known particle precursors¹. By contrast, nitrate ion chemical ionization mass spectrometry (CIMS) field and environmental chamber observations have been interpreted as evidence of nucleation of iodine oxoacids^2,3. Here, we report flow tube laboratory experiments showing that iodine oxides react with nitrate core ions to generate the same ions observed by CIMS instruments. Therefore, we conclude that molecules unlikely to form in the atmosphere in the gas-phase such as iodic acid are not necessary to explain CIMS field measurements, but rather obscure their meaning, whereas iodine oxides explain the field observations and provide a thermochemically feasible mechanism to model the climatic impact of iodine-containing particles. In addition, we propose that a key iodine reservoir species such as iodine nitrate, which we observe as a product of the reaction between iodine oxides and the nitrate anion, can be also detected by CIMS in the atmosphere and has been potentially overlooked in previous field observations⁴.

References

¹ Gómez Martín, J.C., et al. A gas-to-particle conversion mechanism helps to explain atmospheric particle formation through clustering of iodine oxides. Nat. Commun., 11, 4521, https://doi.org/10.1038/s41467-020-18252-8, 2020

² Sipilä, M., et al. Molecular-scale evidence of aerosol particle formation via sequential addition of HIO₃. Nature 537, 532–534, https://doi.org/10.1038/nature19314, 2016.

³ He et al., Role of iodine oxoacids in atmospheric aerosol nucleation, Science, 371, 589–595, https://doi.org/10.1126/science.abe0298, 2021.

⁴ Baccarini et al. Frequent new particle formation over the high Arctic pack ice by enhanced iodine emissions, Nat. Commun., 11, 4924, https://doi.org/10.1038/s41467-020-18551-0, 2020.

How to cite: Gomez Martin, J. C., Lewis, T. R., James, A. D., Plane, J. M. C., and Saiz-Lopez, A.: Ion-molecule reaction laboratory experiments show that iodine oxides explain CIMS atmospheric observations attributed to iodine oxoacids, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-1452, https://doi.org/10.5194/egusphere-egu22-1452, 2022.

Aerosols and clouds are complex systems containing organic and inorganic species, which play central roles in atmospheric chemistry and physics, climate, air pollution and public health. Particularly chemical reactions which occur in the aqueous phase can change the composition and oxidizing capacity of the troposphere via the production and release of trace gas species. Iron(III)-carboxylate complexes impact the chemistry of the atmospheric aqueous phase due to their photochemistry which can trigger free radical chemistry generating reactive oxygen species (ROS), such as HO₂ and H₂O₂. Several studies have highlighted the importance of iodine chemistry due to its capability to influence both oxidative capacity and radiative balance of the atmosphere. A previous work of this group demonstrated a direct link between carbonyl compounds, ROS and iodine chemistry [1]. Furthermore, observed ratios of iodide to iodate in aerosol particles and cloud droplets of the troposphere are much higher than expected [2, 3]. This is indicative of active chemical recycling of iodine between the gas and particle phases, which may be driven by not well understood reductive processes involving iodate, which is thermodynamically the most favored iodine form in the aqueous phase under oxidizing conditions.

We performed coated wall flow tube experiments (CWFT) with aqueous films containing iodate and Iron(III)-citrate (fe-cit) using citric acid (CA) as a matrix since it is an established proxy for oxygenated atmospheric organic matter and with well characterized microphysical properties. The CWFT was coupled with a CE-DOAS instrument in order to detect I₂ [4] resulting from iodate reduction. The results suggest that  photochemistry promotes efficient iodate reduction, linked to the photochemical turnover of the iron(III)-carboxylate complex and to the depletion of the iodine reservoir. We speculate that reduction of iodate is driven by H₂O₂ according to the Bray-Liebhafsky mechanism, where H₂O₂ is provided by fe-cit photochemistry. 

1. P. Corral Arroyo, et al., Atmospheric Chemistry and Physics, (2019)

2. A.R. Baker and C. Yodle, Atmos. Chem. Phys. Discuss., 2021, 1 (2021)

3. T.K. Koenig, et al., Sci Adv, 7, eabj6544 (2021)

4. R. Thalman, et al., Journal of Quantitative Spectroscopy and Radiative Transfer, 147, 171 (2014)

How to cite: Iezzi, L., Reza, M., Finkenzeller, H., Roose, A., Bartels-Rausch, T., Volkamer, R., and Ammann, M.: Iron(III)-carboxylate photochemistry induces iodate reduction, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-1922, https://doi.org/10.5194/egusphere-egu22-1922, 2022.

Recently, Koenig et al. [1] measured both gas phase iodine species and particulate iodine (iodate and iodide) in the lower stratosphere indicating that tropospheric multiphase redox reactions prevent poorly soluble gaseous iodine species from removal by wet deposition leading to injections of inorganic iodine into the lower stratosphere. This may influence stratospheric ozone depletion both indirectly through activation of iodide (I^-) to molecular halogens and directly through the aqueous phase reaction of ozone (O₃) with iodide.  Also in the troposphere, measurements indicate higher than expected iodide to iodate ratios in the aerosol phase [2], suggesting the reaction of O₃ with I^- to be part of iodine cycling throughout the troposphere. The reaction of O₃ with I^- in the aqueous phase, leading to IO^- and to I₂ through the secondary reaction of IO^- with I^-, is rather well established and one of the main iodine source from oceans [3]. However, for the reaction in the aerosol phase, uncertainties exist with respect to the temperature dependence, effects of pH and ionic strength, and also the extent of a surface reaction pathway [4,5].  In addition, Sakamoto et al. [4] have suggested that from this reaction IO(g) may be released. The objectives of this work has been to determine the temperature dependence of the oxidation of I^- by O₃ as well as to have a better understanding of the parameters that lead to IO radical and I₂ formation. We used a trough reactor [5] coupled to Cavity Enhanced – Differential Optical Absorption Spectroscopy (CE-DOAS) [6] to study the reactivity in dilute aqueous solution (273 – 291 K) and in concentrated ammonium sulfate solutions (255 – 291 K). Measurements at varying O₃ mixing ratios indicate a substantial surface reaction component, especially at lower temperature. The IO/I₂ ratio is in the range of 10^-3 – 10^-2. IO formation seems to result predominantly from a surface process. The experiments are also compared with results from theory.

References

[1]        T. K. Koenig et al., PNAS, 117, 4 (2020).

[2]        Baker, A. R., and Yodle, C.: Atmos. Chem. Phys., 21, 13067-13076, 2021.

[3]        L. J. Carpenter et al., Nat. Geosci., 6 (2013).

[4]        Y. Sakamoto et al., J. Phys. Chem. A, 113, 27 (2009).

[5]        C. Moreno et al., Phys. Chem. Chem. Phys., 22 (2020)

[6]        L. Artiglia et al., Nat. Commun., 8 (2017).

[7]        M. Wang et al., Atmos. Meas. Tech., 14, (2021).

How to cite: Ammann, M., Roose, A., Finkenzeller, H., Real, F., Vallet, V., Toubin, C., Gysin, S., Iezzi, L., and Volkamer, R.: IO radical yield from iodide oxidation by ozone on aqueous aerosol proxy surfaces, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-5484, https://doi.org/10.5194/egusphere-egu22-5484, 2022.

Halogen radicals can drastically alter the atmospheric chemistry. In the polar regions, this is made evident by the ozone depletion in the stratosphere (ozone hole) but also by localized destruction of boundary layer ozone during polar springs. These recurrent episodes of catalytic ozone depletion, better known as “ozone depletion events” (ODEs) are caused by enhanced concentrations of reactive bromine compounds. The proposed mechanism by which these compounds are released into the troposphere is called “bromine explosion” - reactive bromine is formed autocatalytically from the condensed phase.

In comparison to previous satellite missions, the TROPOspheric Monitoring Instrument (TROPOMI) onboard ESA’s S5-P satellite allows for an improved localization and a more precise specification of these events due to its superior spatial resolution of up to 3.5 x 5.5 km². Together with the better than daily coverage over the polar regions, this allows for investigations of the spatiotemporal variability of enhanced BrO levels and their relation to different possible bromine sources and release mechanisms.

We present tropospheric BrO column densities retrieved from TROPOMI measurements using Differential Optical Absorption Spectroscopy (DOAS). The advantage of our retrieval is its independence from any external input data. We used a modified k-means clustering and methods from statistical data analysis to separate tropospheric and stratospheric partial columns, thereby relying only on NO₂ and O₃ columns measured by the same instrument. This ensures in particular that the derived tropospheric BrO data set keeps the same spatial resolution as the TROPOMI instrument, because no model data with coarse resolution is used. In a second step, the BrO slant column densities (SCDs) are converted into vertical column densities (VCDs) by using an air mass factor (AMF). These AMFs are derived using a look-up table (LUT) generated by the McArtim radiative transfer model. From this LUT the AMF is calculated for each pixel using measured O₄ SCDs and reflectance data. In a last step, satellite pixels are differentiated by their sensitivity to the lower troposphere using the determined AMF. This allows the exclusion of measurements deemed not sensitive to the troposphere from the dataset and gives a high confidence in the remaining retrieved values.

Our retrieval algorithm avoids systematic biases from external data sets and climatologies and is therefore particularly well suited to compare the retrieved VCDs to additional environmental parameters suspected to alter the release and distribution of BrO during Arctic spring. We examine tropospheric BrO enhancements through case studies, with particular emphasis on the interconnection of ODEs and meteorology. We focus here on the relation of tropospheric BrO to mean sea level pressure, surface air temperature, sea ice age and wind speed and direction. In addition, the spatiotemporal extent of events is studied and compared to WRF-Chem simulations.

How to cite: Schöne, M., Warnach, S., Borger, C., Herrmann, M., Gutheil, E., Beirle, S., Platt, U., and Wagner, T.: Analysis of environmental influences on tropospheric BrO in the Arctic using S5-P/TROPOMI measurements, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-5449, https://doi.org/10.5194/egusphere-egu22-5449, 2022.

Bromine Explosion Events (BEEs) have been observed since the late 1990s in the Arctic and Antarctic during polar spring and play an important role in tropospheric chemistry. In a heterogeneous, autocatalytic, chemical chain reaction cycle, inorganic bromine is released from the cryosphere into the troposphere and depletes ozone often to below detection limit. Ozone is a source of the most important tropospheric oxidizing agent OH and the oxidizing capacity and radiative forcing of the troposphere are thus being impacted. Bromine also reacts with gaseous mercury, thereby facilitating the deposition of toxic mercury, which has adverse environmental impacts. Cold saline surfaces, such as young sea ice, frost flowers, and snow are likely bromine sources during BEEs. Different meteorological conditions seem to favor the development of these events: on the one hand, low wind speeds and a stable boundary layer, where bromine can accumulate and deplete ozone, and on the other hand, high wind speeds above approximately 10 m/s with blowing snow and a higher unstable boundary layer. In high wind speed conditions – occurring for example along fronts of polar cyclones – recycling of bromine on snow and aerosol surfaces may take place aloft.

To improve the understanding of weather conditions and bromine sources leading to the development of BEEs, case studies using high resolution S5P TROPOMI retrievals of tropospheric BrO together with meteorological simulations by the WRF model and Lagrangian transport simulations of BrO by FLEXPART-WRF are carried out. WRF simulations show, that high tropospheric BrO columns observed by TROPOMI often coincide with areas of high wind speeds. This probably points to release of bromine from blowing snow with cold temperatures favoring the bromine explosion reactions. However, some BrO plumes are observed over areas with very low wind speed and a stable low boundary layer.

In addition, BEEs over Ny-Ålesund and the prevailing weather conditions are examined. To monitor the amount of ozone depleted during BEEs, ozone sonde measurements from Ny-Ålesund were used. First evaluations show a drastic decrease in ozone, partly below the detection limit, while measuring enhanced BrO values at the same time. In order to analyze the origin of the BrO plumes observed in Ny-Ålesund, and to investigate transportation routes, FLEXPART-WRF runs are executed for the times of observed ozone depletion.

This work was supported by the DFG funded Transregio-project TR 172 “Arctic Amplification (AC)³“.

How to cite: Zilker, B., Blechschmidt, A.-M., Seo, S., Bougoudis, I., Bösch, T., Richter, A., and Burrows, J. P.: Investigation of weather conditions and tropospheric BrO transport during Bromine Explosion Events in the Arctic and ozone depletion in Ny-Ålesund observed by satellite and ground-based remote sensing, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-9667, https://doi.org/10.5194/egusphere-egu22-9667, 2022.

Polar halogen chemistry has long been known to be active, especially in spring, and has an important influence on the lifetime of some volatile organics, ozone, and mercury. Reactive chlorine and bromine species, produced from snow and aerosols, can have significant impacts on the oxidative capacity of the polar boundary layer. However, halogen production mechanisms from snow remain highly uncertain, making it challenging to include descriptions of halogen snow emissions in models and to understand the impact on atmospheric chemistry. In this work, we investigate the role of Arctic chlorine and bromine emissions from snow on boundary layer oxidation processes using a one-dimensional atmospheric chemistry and transport model (PACT-1D). We explore the impact of halogen snow emissions and boundary layer dynamics on atmospheric chemistry by modelling primary emissions of Cl₂ and Br₂ from snow, and heterogeneous recycling reactions on snow and aerosols. We present a two-day case study from the 2009 Ocean-Atmosphere-Sea Ice-Snowpack (OASIS) campaign at Utqiagvik, Alaska. 

The model reproduces both the diurnal cycle and high quantity of Cl₂ measured, along with the observed concentrations of Br₂, BrO, and HOBr. Due to a combination of chemical emissions, recycling, vertical mixing, and atmospheric chemistry, reactive chlorine is confined to the lowest 15 m of the atmosphere, whilst bromine impacts chemistry up to the boundary layer height. Following the inclusion of halogen emissions and recycling, HO_x concentrations (HO_x = OH+HO₂) increase by as much as a factor of 30 at the surface at mid-day. Consequently, volatile organic compound (VOC) lifetimes are significantly reduced within a shallow layer near the surface, due to chlorine atoms from Cl₂ snow emissions and increased HO_x attributable to halogen chemistry.

How to cite: Ahmed, S., Thomas, J. L., Tuite, K., Stutz, J., Flocke, F., Orlando, J. J., Hornbrook, R. S., Apel, E. C., Emmons, L. K., Helmig, D., Boylan, P., Huey, L. G., Hall, S. R., Ullmann, K., Cantrell, C. A., and Fried, A.: Reactive halogen chemistry in the Arctic boundary layer over snow during spring: A 1D modelling case study, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7516, https://doi.org/10.5194/egusphere-egu22-7516, 2022.

The tropospheric Ozone Depletion Event (ODE), first observed at Barrow, Alaska (now known as Utqiagvik), is a phenomenon that occurs during the springtime of Arctic. During ODEs, the surface ozone declines rapidly from a background level of 40-60 ppbv to a few ppbv, within a couple of days or even hours. In the present study, we made a three-dimensional simulation of ODEs occurring during March 28 to April 5, 2019 at Barrow and its surrounding areas, using a 3-D multi-scale air quality model, CMAQ.

Three ODEs observed at Barrow were accurately captured in the model and analyzed thoroughly using the tool of process analysis. It was found that the first ODE occurred on March 29 was mostly caused by a transport of a low-ozone air to the west of the Chukchi Sea. In contrast, the occurrence of another ODE between March 30 and 31 is attributed to a horizontal transport of the ozone-lacking air from the Beaufort sea. This ozone-lacking air ascribes to a release of abundant sea-salt aerosols from the Bering Strait under a strong wind condition, resulted from a cyclone formed at the Chukotka Peninsula. Afterwards, bromine is activated from the sea-salt aerosols, consuming ozone over the sea. It was found that over the sea, the consumption of the surface ozone due to chemical processes reaches as large as 10 ppb. During this ODE, ozone drops to a level lower than 5 ppb. In contrast, BrO attains a maximum of approximately 100 ppt. This ozone-lacking air over the sea thus leads to the partial ODE occurring at Barrow through the horizontal transport. The third ODE occurring on April 2 was also found to be mainly caused by the horizontal advection from the sea. Later on, on April 3, ozone in the boundary layer is replenished by the strong vertical diffusion of ozone-rich air from the free troposphere, leading to the termination of this ODE. 

Our 3-D simulations also indicate that the vertical properties of the atmosphere exert a remarkable impact on the vertical distribution of chemical species. Under strong uplifting and warm underlying surfaces, the ozone-lacking air can break through the top of the boundary layer, affecting the free atmosphere. 

How to cite: Li, S. and Cao, L.: A three-dimensional simulation and process analysis of tropospheric Ozone Depletion Events (ODEs) during the springtime of Arctic using CMAQ, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-132, https://doi.org/10.5194/egusphere-egu22-132, 2022.