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Laboratory studies of atmospheric chemistry characterize the nature of atmospherically relevant processes down to the molecular level, providing fundamental information used to assess how human activities drive environmental phenomena such as climate change, urban air pollution, ecosystem health, indoor air quality, and stratospheric ozone depletion. Laboratory studies have a central role in addressing the incomplete fundamental knowledge of atmospheric chemistry. This article highlights the evolving science needs for this community and emphasizes how our knowledge is far from complete, hindering our ability to predict the future state of our atmosphere and to respond to emerging global environmental change issues. Laboratory studies provide rich opportunities to expand our understanding of the atmosphere via collaborative research with the modeling and field measurement communities, and with neighboring disciplines.

Iodine at the ocean's surface impacts climate and health by removing ozone (O 3) from the troposphere both directly via ozone deposition to seawater and indirectly via the formation of iodine gases that are released into the atmosphere. Here we present a new box model of the ocean surface microlayer that couples oceanic O 3 dry deposition to inorganic chemistry to predict inorganic iodine emissions. This model builds on the previous work of , improving both chemical and physical processes. This new box model predicts iodide depletion in the top few micrometres of the ocean surface due to rapid chemical loss to ozone competing with replenishment from underlying water. From this box model, we produce parameterized equations for HOI and I 2 emissions, which are implemented into the global chemical transport model GEOS-Chem along with an updated sea surface iodide climatology. Compared to the previous model, inorganic iodine emissions from some tropical waters decrease by as much as half, while higher-latitude emissions increase by a factor of ≫10. With these large local changes, global total inorganic iodine emissions increased by ∼49 % (2.99 to 4.48 Tg) compared to the previous parameterization. This results in a negligible change in average tropospheric OH (<0.2 %) and tropospheric methane lifetime (<0.2 %). The annual mean tropospheric O 3 burden decreases (-1.5 % to 325 Tg); however, higher-latitude surface O 3 concentrations decrease by as much as 20 %. [ABSTRACT FROM AUTHOR]

Non-methane volatile organic compounds (NMVOCs) generate ozone (O 3) when they are oxidised in the presence of oxides of nitrogen, modulate the oxidative capacity of the atmosphere and can lead to the formation of aerosol. Here, we assess the capability of a chemical transport model (GEOS-Chem) to simulate NMVOC concentrations by comparing ethane, propane and higher-alkane observations in remote regions from the NOAA flask Network and the World Meteorological Organization's Global Atmosphere Watch (GAW) network. Using the Community Emissions Data System (CEDS) inventory, we find a significant underestimate in the simulated concentration of both ethane (35 %) and propane (64 %), consistent with previous studies. We run a new simulation in which the total mass of anthropogenic NMVOC emitted in a grid box is the same as that used in CEDS but with the NMVOC speciation derived from regional inventories. For US emissions, we use the National Emissions Inventory (NEI); for Europe, we use the UK National Atmospheric Emissions Inventory (NAEI); and for China, we use the Multi-resolution Emission Inventory model for Climate and air pollution research (MEIC). These changes lead to a large increase in the modelled concentrations of ethane, improving the mean model bias from - 35 % to - 4 %. Simulated propane also improves (from - 64 % to - 48 % mean model bias), but there remains a substantial model underestimate. There were relatively minor changes to other NMVOCs. The low bias in simulated global ethane concentration is essentially removed, resolving one long-term issue in global simulations. Propane concentrations are improved but remain significantly underestimated, suggesting the potential for a missing global propane source. The change in the NMVOC emission speciation results in only minor changes in tropospheric O 3 and OH concentrations. [ABSTRACT FROM AUTHOR]

The reaction between ozone and iodide is one of the main drivers of tropospheric ozone deposition to the ocean due to the ubiquitous presence of iodide in the ocean surface and its rapid reaction with ozone. Despite the importance of this sea surface reaction for tropospheric ozone deposition and also as the major source of atmospheric iodine, there is uncertainty in its rate and dependence on aqueous-phase temperature. In this work, the kinetics of the heterogeneous second-order reaction between ozone and iodide are investigated using conditions applicable to coupled ocean–atmosphere systems (1 × 10 -7 –1 × 10 -5 M iodide; 40 ppb ozone; 288–303 K ; 15.0 psi). The determined Arrhenius parameters of A = 5.4 ± 23.0 × 10 10 M-1s-1 and Ea = 7.0 ± 10.5 kJmol-1 show that the reaction has a negligible positive temperature dependence, which could be weakly negative within errors. This is in contrast to a previous study that found a strong positive activation energy and a pre-exponential factor many orders of magnitude greater than determined here. The re-measured kinetics of ozone and iodide were used to constrain a state-of-the-art sea surface microlayer (SML) model. The model replicated results from a previous laboratory study of the temperature dependence of hypoiodous acid (HOI) and molecular iodine (I2) emissions from an ozone-oxidised iodide solution. This work has significance for the global modelling of the dry deposition of ozone to the ocean and the subsequent emissions of iodine-containing species, thus improving the understanding of the feedback between natural halogens, air quality and climate change. [ABSTRACT FROM AUTHOR]

The North Atlantic Climate System: Integrated Study (ACSIS) was a large multidisciplinary research programme funded by the United Kingdom's Natural Environment Research Council (NERC). ACSIS ran from 2016-22 and brought together around 80 scientists from seven leading UK-based environmental research institutes to deliver major advances in understanding North Atlantic climate variability and extremes. Here we present an overview of the data generated by the ACSIS programme. The datasets cover the full North Atlantic System comprising: the North Atlantic Ocean, the atmosphere above it including its composition, Arctic Sea Ice and the Greenland Ice Sheet. Atmospheric composition datasets include measurements from 7 aircraft campaigns (between 3 and 10 flights each, 0-10 km altitude range) in the north eastern Atlantic (~40° W-5° E,~15° N-55° N) made at intervals of from 6 months to 2 years between February 2017 and may 2022. The flights measured chemical species (including greenhouse gases, ozone precursors and VOCs) and aerosols (organic, SO4, NH4, NO3, and nss-Cl) (https://dx.doi.org/10.5285/6285564c34a246fc9ba5ce053d85e5e7 (FAAM et al. (2024)). Ground based stations at the Cape Verde Atmospheric Observatory (CVAO), Penlee Point Atmospheric Observatory (PPAO) and Plymouth Marine Laboratory (PML) recorded ozone, ozone precursors, halocarbons, as well as greenhouse gases (CO2, methane), SO2 and photolysis rates. (CVAO, http://catalogue.ceda.ac.uk/uuid/81693aad69409100b1b9a247b9ae75d5, National Centre for Atmospheric Science et al. (2014)), O3 and CH4 (PPAO, https://catalogue.ceda.ac.uk/uuid/8f1ff8ea77534e08b03983685990a9b0 (Plymouth Marine Laboratory and Yang (2024)) and aerosols (PML, https://dx.doi.org/10.5285/e74491c96ef24df29a9342a3d57b5939, Smyth (2024)). Complementary model simulations of atmospheric composition were performed with the UK Earth System Model, UKESM1, for the period 1982 to 2020 using CMIP6 historical forcing up to 2014 and SSP3-7.0 scenario from 2015-2020. Model temperature and winds were relaxed towards ERA reanalysis. Monthly mean model data for ozone, NO, NO2, CO, methane, stratospheric ozone tracers and 30 regionally emitted tracers are available to download (https://data.ceda.ac.uk/badc/acsis/UKESM1-hindcasts, Abraham (2024)). ACSIS also generated new ocean heat content diagnostics https://doi.org/10/g6wm, https://doi.org/10/g8g2, Moat et al. (2021a-b) and gridded temperature and salinity based on objectively mapped Argo measurements https://doi.org/10.5285/fe8e524d-7f04-41f3-e053-6c86abc04d51 (King (2023). An ensemble of atmosphere-forced global ocean-sea ice simulations using the NEMO-CICE model was performed with horizontal resolutions of 1/4° and 1/12° covering the period 1958-2020 using several different atmosphere reanalysis based surface forcing datasets, supplemented by additional global simulations and standalone sea ice model simulations with advanced sea ice physics using the CICE model (http://catalogue.ceda.ac.uk/uuid/770a885a8bc34d51ad71e87ef346d6a8, Megann et al. (2021e). Output is stored as monthly averages and includes 3D potential temperature, salinity, zonal, meridional and vertical velocity; 2D sea surface height, mixed layer depth, surface heat and freshwater fluxes, ice concentration and thickness and a wide variety of other variables. In addition to the data presented here we provide a brief overview of several other datasets that were generated during ACSIS which have been described previously in the literature. [ABSTRACT FROM AUTHOR]

Iodine at the ocean's surface impacts climate and health by removing ozone (O3) from the troposphere both directly, via ozone deposition to seawater, and indirectly via the formation of iodine gases which are released into the atmosphere. Here we present a new box model of the ocean surface microlayer that couples oceanic O3 dry deposition to inorganic chemistry to predict inorganic iodine emissions. This model builds on the previous work of Carpenter et al. (2013), improving both chemical and physical processes. This new box model predicts iodide depletion in the top few micrometres of the ocean surface, due to rapid chemical loss to ozone competing with replenishment from underlying water. From this box model, we produce parameterised equations for HOI and I2 emissions which are implemented into the global chemical transport model GEOS-Chem. Compared to the previous model, inorganic iodine emissions from tropical waters decrease by as much as half, while higher latitude emissions increase by a factor of ~ 10. Despite these large local changes, global total inorganic iodine emissions increased by only ~ 4% (2.83 Tg to 2.95 Tg) compared to the previous parameterization. This results in a negligible change in average tropospheric OH (<0.1%) and tropospheric methane lifetime (<0.1%). The annual mean tropospheric O3 burden changes negligibly (an increase of 0.2% to 330 Tg), however, higher latitude surface O3 concentrations decrease by as much as 15% with equatorial O3 concentrations increasing by up to 10%. [ABSTRACT FROM AUTHOR]

The reaction between ozone and iodide is one of the main drivers of tropospheric ozone deposition to the ocean, due to the ubiquitous presence of iodide in the ocean surface and its rapid reaction with ozone. Despite the importance of this sea surface reaction for tropospheric ozone deposition, and also as the major source of atmospheric iodine, there is uncertainty in its rate and dependence on aqueous phase temperature. In this work, the kinetics of the heterogeneous second order reaction between ozone and iodide were investigated using conditions applicable to coupled ocean-atmosphere systems (1×10-7 - 1×10-5 M [iodide], 40 ppb ozone, 288 - 303 K, 15.0 psi). The Arrhenius parameters determined of A = 1.0 ± 4.6 ×1011 M-1 s-1 and Ea = 8.5 ± 10.9 kJ mol-1 show that the reaction has a negligible positive temperature dependence, which could be weakly negative within errors. This is in contrast to a previous study that found a strong positive activation energy and a pre-exponential factor many orders of magnitude greater than determined here. The re-measured kinetics of ozone and iodide were used to constrain a state-of-the-art sea surface microlayer (SML) model. The model replicated results from a previous laboratory study of the temperature dependence of hypoiodous acid (HOI) and molecular iodine (I2) emissions from an ozoneoxidised iodide solution. This work has significance for global modelling of dry deposition of ozone to the ocean and the subsequent emissions of iodine-containing species, thus improving understanding of the feedbacks between natural halogens, air quality, and climate change. [ABSTRACT FROM AUTHOR]

Non-Methane Volatile Organic Compounds (NMVOCs) generate ozone (O3) when they are oxidized in the presence of oxides of nitrogen, modulate the oxidative capacity of the atmosphere and can lead to the formation of aerosol. Here, we assess the capability of a chemical transport model (GEOS-Chem) to simulate NMVOC concentrations by comparing ethane, propane and higher alkane observations in remote regions from the NOAA Flask Network and the World Meteorological Organization's 5 Global Atmosphere Watch (GAW) network. Using the Community Emissions Data System (CEDS) inventory we find a significant underestimate in the simulated concentration of both ethane (35%) and propane (64%), consistent with previous studies. We run a new simulation where the total mass of anthropogenic NMVOC emitted in a grid box is the same as that used in CEDS, but with the NMVOC speciation derived from regional inventories. For US emissions we use the National Emissions Inventory (NEI), for Europe we use the UK National Atmospheric Emissions Inventory (NAEI), and for China, the Multi-resolution Emission Inventory for China (MEIC). These changes lead to a large increase in the modelled concentrations of ethane, improving the mean model bias from -35% to -3.8%. Simulated propane also improves (from -64% to -48.0% mean model bias), but there remains a substantial model underestimate. There were relatively minor changes to other NMVOCs. The low bias in simulated global ethane concentration is essentially removed, resolving one long-term issue in global simulations. Propane concentrations are improved but remain significantly underestimated, suggesting the potential for a missing global propane source. The change in the NMVOC emission speciation results in only minor changes in tropospheric O3 and OH concentrations. [ABSTRACT FROM AUTHOR]