Events

Laboratory experiments show the transition between iodine precursor gas phase molecules and molecular clusters of growing size.

New atmospheric particle formation is one is the largest uncertainties in climate simulations. Although it is known for the last two decades that iodine oxides form new particles in the lower atmosphere, its inclusion in atmospheric models is hindered by a lack of understanding of the first steps of the photochemical gas-to-particle conversion mechanism.

In this study, we combine laboratory experiments, theory and modelling to reveal the mechanism that connects oceanic iodine emissions and atmospheric particle formation. The results show that the gas to particle conversion proceed primarily via clustering of iodine oxides and that the composition of nanometric particles (iodic acid) is due to the processing of these clusters in the presence of atmospheric humidity. This study highlights the remarkable capacity that iodine oxides have to form new particles.

This new mechanism is climatically relevant since the global iodine emissions have tripled in the last 70 years following the increase in anthropogenic ozone pollution, and it is expected that this increase will continue in the future, thereby pointing to a more prominent role of iodine particle formation in the future atmosphere.

Juan Carlos Gómez Martín, Thomas R. Lewis, Mark A. Blitz, John M.C. Plane, Manoj Kumar, Joseph S. Francisco and Alfonso Saiz-Lopez. A gas-to-particle conversion mechanism helps to explain atmospheric particle formation through clustering of iodine oxides, Nature Communications.  DOI: 10.1038/s41467-020-18252-8

(Photograph by Alfons Puertas / Observatorio Fabra)

Natural halogens are estimated to destroy 10–20 % of tropospheric O3. This study uses an Earth system model to project varying natural halogen emissions and investigate their impact on tropospheric O3 over the 21st century.

New research, led by CSIC, CONICET, NCAR and Lancaster University, shows that emissions of natural halogens (chlorine, bromine and iodine) buffer the increase in global tropospheric ozone (O3), an air pollutant and greenhouse gas, as climate changes during the 21st century.  At present, natural halogens (dominated by ocean emissions) are estimated to destroy 10–20 % of global tropospheric O3 burden.

The findings in a new Nature Climate Change paper reveal a strong buffering capacity of natural halogens controlling tropospheric O3, as the climate warms. In this century, the atmosphere and its composition will experience profound disturbances associated with socio-economic developments, such as changes in greenhouse gas and pollutant emissions. Notably, halogen-driven tropospheric O3 destruction is projected to remain unchanged.

In this study, researchers explored long-term simulations using a state-of-the-art Earth system model to project varying natural halogen emissions and investigate their impact on tropospheric O3 abundances over the 21st century. The role that different drivers play on the future atmosphere results in highly heterogeneous tropospheric O3 destruction with marked hemispheric, regional, and vertical asymmetries. Moreover, the largest O3 losses due to natural halogens (up to 70 % compared to present) are predicted over polluted coastal regions, with important benefits for air quality.

The authors of the study hope that these findings will open a “new” focus of research on natural halogen chemistry –as a key component of the troposphere– in coming years, which destroys a large fraction of O3 at the present and will determine its future abundance and distribution in an ever-changing atmosphere.

Fernando Iglesias-Suarez, Alba Badia, Rafael P. Fernandez, Carlos A. Cuevas, Douglas E. Kinnison, Simone Tilmes, Jean-François Lamarque, Ryan Hossaini and Alfonso Saiz-Lopez. Natural halogens buffer tropospheric ozone in a changing climate. Nature Climate Change. DOI: 10.1038/s41558-019-0675-6

Simulations at the air-water interface shows that IONO2 does not react directly with iodine acids, but forms a halogen bond, for the first time proposed to occur on an atmospheric aqueous surface.

The atmospheric chemistry of iodine is important because of its role in catalytic ozone loss and new particle formation, which have an influence in the energy balance of the atmosphere. Iodine nitrate (IONO2) is one of the main reservoir species in the atmospheric iodine cycle. It is formed via the reaction of iodine oxide and nitrogen dioxide. The primary fate of IONO2 is believed to be, besides photolysis, uptake by aerosol surfaces, leading to particulate iodine activation.

In this study, we have conducted simulations on the interaction of IONO2 with the iodine acids (HIO3 and HIO2) that compose atmospheric ultrafine iodine particles. The results indicate that IONO2 does not react directly with these iodine acids, but forms an unusual kind of interaction with them within a few picoseconds, which is characterized as halogen bonding. The halogen bond-driven HIO3−IONO2 complex at the air−water interface undergoes deprotonation and exists as IO3 −−IONO2 anion, whereas the HIO2−IONO2 complex does not exhibit any proton loss to the interfacial water molecules. The gas-phase quantum chemical calculations suggest that the HIO3−IONO2 and HIO2−IONO2 complexes have appreciable stabilization energies, which are significantly enhanced upon deprotonation of iodine acids, indicating that these halogen bonds are fairly stable. These IONO2- induced halogen bonds explain the rapid loss of IONO2 to background aerosol. Moreover, they appear to work against iodide formation. Thus, they may play an important role in enhancing the amount of atmospherically nonrecyclable iodine (iodate) in marine aerosol.

Manoj Kumar, Tarek Trabelsi, Juan Carlos Gómez Martín, Alfonso Saiz-Lopez and Joseph S. Francisco. HIOx-IONO2 dynamics at the air-water interface: Revealing the existence of a halogen bond at the atmospheric aerosol surface. Journal of the American Chemical Society. DOI: 10.1021/jacs.0c05232

This study presents the first observation of an important intermediate in the oxidation of DMS, a compound naturally emitted from the oceans that produces sulfate aerosols, which in turn affect cloud formation and climate.

Dimethyl sulfide (DMS, (CH3)2S), emitted by the oceans, is the most abundant biological source of sulfur in the marine atmosphere. Atmospheric DMS is oxidized to condensable products that form secondary aerosols that affect the Earth's radiative balance by scattering solar radiation and serving as cloud condensation nuclei.

An international study with the participation of the IQFR, presents the first detection in the atmosphere of hydroperoxymethyl thioformate (HPMTF, HOOCH2SCHO), an intermediate product in the oxidation scheme of DMS. This product, identified through global-scale airborne observations during the ATom campaign from the Gulfstream-V research aircraft of the NCAR (National Center for Atmospheric Research in the US), is therefore an important marine sulfur reservoir. These observations have been made using the chemical ionization mass spectrometry (TOF-CIMS) technique.

Observationally constrained theoretical calculations of gas phase kinetics show that more than 30% of oceanic DMS emitted to the atmosphere forms HPMTF. Coincident particle measurements suggest a strong link between HPMTF concentration and new particle formation and growth.

Details of the oxidation mechanisms of DMS are critical in defining the interactions of its atmospheric chemistry with the climate. Studies of DMS oxidation have focused on the terminal  products, sulfur dioxide (SO2) and methanesulfonic acid (MSA, CH3SO3H). Most of the intermediates in this complex oxidation scheme have not even been detected. Therefore, there is a great uncertainty about the DMS products branching and oxidation timescales. The introduction of this new oxidation mechanism in global atmospheric models shows the implications of these observations, with reductions of up to 50% and 30% in sulfur dioxide and sulfate levels respectively. Hence the importance of including this mechanism in atmospheric models, to improve representation of key linkages between the biogeochemistry of the ocean, marine aerosol formation and growth, and their combined effects on climate.

Patrick R. Veres, J. Andrew Neuman, Timothy H. Bertram, Emmanuel Assaf, Glenn M. Wolfe, Christina J. Williamson, Bernadett Weinzierl, Simone Tilmes, Chelsea Thompson, Alexander B. Thames, Jason C. Schroder, Alfonso Saiz-Lopez, Andrew W. Rollins, James M. Roberts, Derek Price, Jeff Peischl, Benjamin A. Nault, Kristian H. Møller, David O. Miller, Simone Meinardi, Qinyi Li, Jean-François Lamarque, Agnieszka Kupc, Henrik G. Kjaergaard, Douglas Kinnison, Jose L. Jimenez, Christopher M. Jernigan, Rebecca S. Hornbrook, Alan Hills, Maximilian Dollner, Douglas A. Day, Carlos A. Cuevas, Pedro Campuzano-Jost, James Burkholder, T. Paul Bui, William H. Brune, Steven S. Brown, Charles A. Brock, Ilann Bourgeois, Donald R. Blake, Eric C. Apel and Thomas B. Ryerson . Global airborne sampling reveals a new dimethyl sulfide oxidation mechanism in the marine atmosphere. Proceedings of the National Academy of Sciences (PNAS). DOI: https://doi.org/10.1073/pnas.1919344117