Events

The atmosphere of Venus has abundant SO₂ and sulfuric acid particles. The ultraviolet destruction of SO₂ is expected to produce sulfur particles, built up from atomic S to S₂, then S₄ and finally S₈.

Here we explore how this process is initiated, how S₂ is formed. One possibility is to form S₂ from two sulfur atoms, that is, reaction of S and S. Molecules of S₂ and S₂ can then combine to form S₄, and so on. Sulfur particles can form either by condensation of S₈ or by condensation of S₂, S₄ and other allotropes which then rearrange to form condensed S₈. This paper explores the initial S₂ formation by an alternative pathway by using computational chemistry.

The results suggest a new pathway for S₂ formation, the SO and S₂O, which is much faster than combining two S atoms to make S₂, thereby providing a faster route to sulfur particle formation and…

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Methane (CH₄) is a greenhouse gas with the second-largest contribution to global warming after CO₂. Unlike the inert gas CO₂, CH₄ actively participates in atmospheric chemistry. A better understanding of the global CH₄ budget (i.e., sources and sinks) is vital to constrain its atmospheric levels and radiative forcing in the 21^st century, as well as to guide climate mitigation efforts, e.g., policies to fulfil the Paris agreement. Previous studies focus on CH₄ sources with less attention on its losses, which have been reported to be the direct reactions with the OH radical (the dominant sink) and Chlorine atoms (Cl). Current chemistry-climate models tend to underestimate the lifetime of CH₄, suggesting uncertainties in its sources and sinks.

Over the past decades, a large and growing body of observational evidence has demonstrated the ubiquitous existence of…

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Atmospheric SO3 is an important intermediate in the formation of sulfuric acid, which is a critical component of acid rain, the stratospheric aerosol layer, new particle formation and secondary aerosol. The formation of gaseous H2SO4 proceeds through the reaction of SO3 + 2H2O. While this reaction has been subject of several laboratory studies, additional removal mechanisms of SO3 are largely unknown and are the motivation of this work.
The new SO3 + HONO2 reaction can potentially compete well with the SO3 + 2H2O reaction between 25 and 35 kms in the atmosphere, as well as the OH + HONO2 reaction. We also suggest the potential for SO3 reactions with organic acids to generate organosulfates without the need for heterogeneous chemistry.
 

Bo Long, Yu Xia, Javier Carmona-García, Juan Carlos Gómez Martín, John M. C. Plane, Alfonso Saiz-Lopez, Daniel…

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These observations provide evidence of autocatalytic iodine release from atmospheric aerosol

Atmospheric iodine, dominated by ocean emissions, is important in atmospheric chemistry for two main reasons, a) its remarkable capacity to form new particles that can grow to cloud condensation nuclei (CCN) sizes, thereby establishing a direct link between iodine emissions and CCN in remote regions; b) iodine is a very efficient ozone depleting substance in the troposphere. The changing evolution of these two processes is particularly relevant since global iodine emissions have tripled in the last 70 years.

Key to the abovementioned atmospheric implications is the recycling of reactive iodine from heterogeneous reactions on seasalt aerosols. This process was hypothesized over two decades ago to proceed via aerosol uptake of gaseous hypoiodous acid (HOI) and its…

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Iodine chemistry is an important driver of new particle formation in the marine and polar boundary layers. There are, however, conflicting views about how iodine gas-to-particle conversion proceeds. Laboratory studies indicate that the photooxidation of iodine produces iodine oxides (IxOy), which are well-known particle precursors. By contrast, nitrate anion chemical ionization mass spectrometry (CIMS) observations in field and environmental chamber studies have been interpreted as evidence of a dominant role of iodic acid (HIO3) in iodine-driven particle formation.
These experimental results, aided by theoretical calculations, solve these discrepancies by showing that both IxOy and HIO3 are involved in atmospheric new particle formation. I2Oy molecules (y = 2, 3, and 4) react with nitrate core ions to generate mass spectra similar to those obtained…

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(Photograph by Andrea Baccarini)

Measurements in the Arctic show that iodine forms particles that grow to cloud condensation nuclei.

New atmospheric particle formation is one is the largest uncertainties in climate simulations. The source of new particles in the central Arctic has remained elusive since the first aerosol measurements in the Arctic in 1991.

In this study, we report observation that show iodine to be the main source of new particles in the central Arctic. The observations were made during an expedition to the central Arctic in 2018 (Microbiology-Ocean-Cloud-Coupling in the High Arctic, MOCCHA) onboard the Swedish icebreaker Oden. The results not only highlight the remarkable capacity that iodine oxides have to form new particles but also show that these new particles grow to cloud condensation nuclei (CCN) sizes, thereby establishing a direct…

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