Hydrofluoroolefins (HFOs) are replacing high-GWP hydrofluorocarbons (HFCs) across multiple applications including foam blowing, refrigeration, and aerosols, but their atmospheric degradation and climate consequences remain uncertain. We use the GEOS-Chem 3-D chemical transport model, supported by AtChem2 box-model simulations, to develop a complete representation of the atmospheric chemistry and fate of HFO-1234ze(E) and its key intermediate product, trifluoroacetaldehyde (CF3CHO). We focus on HFO-1234ze(E) as it is the dominant isomer in commercial use. The model includes newly measured CF3CHO photolysis quantum yields to form fluoroform (HFC-23), the recently identified chemical pathways of HFO-1234ze(E) ozonolysis and CF3CHO reversible reaction with HO2, and explicit wet and dry deposition parameterisations. Using observationally constrained global HFO-1234ze(E) emissions of 15 Gg year-1, simulated HFO-1234ze(E) surface mixing ratios agree well with 2020-2024 observations at 8 Advanced Global Atmospheric Gases Experiment (AGAGE) network sites. We find that 99.6% of HFO-1234ze(E) is removed by reaction with OH, with the remaining 0.4% lost to ozonolysis. Sensitivity tests for effective Henry's law constants spanning 10-106 M atm-1 show sensitivity of CF3CHO fate to up to 104 M atm-1 and saturation at higher . Using an upper bound of 105 M atm-1, deposition accounts for approximate to 51% of total CF3CHO loss in GEOS-Chem (20% dry, 31% wet), with photolysis contributing approximate to 33% and OH reaction approximate to 15%. The reversible reaction with HO2 contributes around 1% to net CF3CHO loss due to rapid conversion of the reaction products back to reactants. We calculate a total (direct + indirect) GWP100 for HFO-1234ze(E) of 11.4+3.1-1.9, with CF3CHO photolysis to HFC-23 contributing 8.2+3.1-1.9. We also estimate a maximum potential formation of 4.5 Gg year-1 of trifluoroacetic acid (TFA) under current emissions assuming complete conversion of wet-deposited CF3CHO from HFO-1234ze(E), suggesting a potential unrecognised TFA source from all CF3CHO sources.

Alaska has one of the world's largest glaciated areas and is highly sensitive to climate change. Alaskan glaciers currently contribute about a third of the global sea level rise, with tidewater glaciers playing a significant role through rapid retreat. Meteorological observations in this region are insufficient to assess climatic influences on the tidewater glacier cycle, and existing model datasets are either too coarse or cover too short a period. This study reconstructs the regional climate of southern Alaska by downscaling the NOAA-CIRES-DOE 20th Century Reanalysis (20CRv3) from 1836–2015 using the Weather Research and Forecasting model (WRF) to produce a high-resolution 4-km dataset. The new downscaled dataset (20CRv3-WRF) was validated for 1981–2015 against observational records (GSOD) and the Parameter-elevation Regression on Independent Slopes Model (PRISM) datasets and compared to European Centre for Medium-Range Weather Forecasts (ECMWF) Reanalysis v5 (ERA5). Compared to the observational records, 20CRV3-WRF performed well for annual mean temperature (0.61 ≤ r ≤ 0.96) and moderately for annual precipitation (0.16 ≤ r ≤ 0.76). For temperature, 20CRv3 downscaling output was more consistent with PRISM than with the coarser resolution ERA5, suggesting a more accurate representation of temperature than the reanalysis. Precipitation was mostly overestimated in comparison to observations. The spatial variability of precipitation was better represented in 20CRv3-WRF than ERA5. The results demonstrate that 20CRv3-WRF provides a reliable high-resolution dataset to assess the influence of climate on southern Alaskan tidewater glaciers, enabling future studies requiring long-term atmospheric data.

Bromine radicals released from sea ice, snow, and marine sources play a critical role in the atmospheric chemistry of polar regions. The Chemical and Mesoscale Mechanisms of Polar Cell Aerosol Nucleation (CAMMPCAN) ship campaign conducted in coastal East Antarctica over two 6-month periods in 2017-18 and 2018-19 provides a unique dataset to identify the environmental drivers of bromine variability in Antarctic spring and summer. In this study, we used CAMMPCAN chemical and meteorological observations combined with reanalysis data from the Modern Era Retrospective Analysis for Research and Applications version 2 (MERRA-2) and satellite-based sea ice data from the National Snow and Ice Data Center to select variables that showed statistically significant correlation with bromine monoxide (BrO) partial columns measured during CAMMPCAN. We then used those variables in principal component analysis and subsequent principal component regression to identify dominant modes of Antarctic environmental variability and their impacts on lower tropospheric BrO. Comparing our three dominant Antarctic principal components to those from a similar analysis conducted previously for the Arctic (Swanson et al., 2020), we found only one mode with clear overlap, representing a vertical mixing mode in which low-pressure systems mix BrO and its precursors into the lower troposphere. We also identified an Antarctic mode describing conditions favourable for blowing snow, similar to the combined effect of two modes from the Arctic analysis but more clearly disambiguated here due to the inclusion of sea ice data in our analysis. The third Antarctic mode, attributed to an ocean source (biological activity and/or sea salt aerosol), was particularly important in summer. The principal component regression model developed from these modes showed moderate skill in predicting BrO partial columns in the lowest 2 km of the troposphere (R = 0.51), a significant improvement over the Arctic-based regression model (R = 0.08). Neither model could reproduce the observed variability in BrO in the lowest 200 m. Finally, we applied the same analysis to coincident CAMMPCAN observations of gaseous elemental mercury and found regression of our three dominant modes could explain nearly 50% of observed mercury variability (R = 0.69). Our results reinforce the importance of sea ice and ocean processes in bromine cycling in coastal East Antarctica and highlight the need to consider Antarctic-specific processes in mechanistic models of atmospheric bromine chemistry.

Aromatics are an important class of volatile organic compounds with impacts on human health. The impacts of aromatics and their oxidation products vary. While the chemistry and major pathways of the precursor aromatics are relatively well understood, the same is not true for their phenolic oxidation products. Here, we use new observations of aromatic oxidation products collected during the Korea-United States Air Quality aircraft campaign to evaluate the aromatic chemical mechanism in the GEOS-Chem v13.4.0 chemical transport model. Based on these results, we implement changes to emissions, add ethylbenzene chemistry, and introduce phenol production from ethylbenzene and toluene oxidation. These changes improve simulation of benzene (reducing normalized mean bias from 24% to -9%) and phenol (-71% to -42%). Model biases increase for toluene, xylene, and cresol, but simulated mixing ratios remain within measurement uncertainties and observed interquartile ranges. We identify potential toluene emission overestimates from petrochemical complexes in Ulsan and Daesan and underestimates from the Daegu dyeing industrial complex, and underestimates of benzene emissions from China. Using the updated model, we find benzene and toluene contribute equally to phenol production in the boundary layer (accounting for 40% of phenol production each), and that toluene and ethylbenzene are atmospherically relevant precursors of phenol. Phenol and cresol loss is found to be dominated by OH oxidation (73% for both phenol and cresol). We find that benzaldehyde is the dominant source of nitrophenol production (67%), although phenol dominates nitrophenol production at night.

In Pérez-Peña et al. (DOI: https://doi.org/10.1039/d3ea00120b), we used a suite of box model simulations to determine how trifluoroacetaldehyde (CF3CHO) produced from HFO-1234ze is lost in the atmosphere and how much fluoroform (CHF3 or HFC-23) could potentially be produced as a result. For the first time in any modelling study, our simulations included both a minor CF3CHO photolytic loss channel leading to CHF3 production and physical removal of CF3CHO via wet and dry deposition. In their comment, Sulbaek Andersen, Nielsen, and Franklin query the assumptions used to simulate these processes. Here, we show that the importance of the photolytic loss pathway remains a matter of community debate and that our results are relatively insensitive to assumptions underlying simulation of deposition. We reiterate the need for measurements of CF3CHO physical properties to reduce the uncertainties in these processes and pave the way for more sophisticated models.

The natural cycles of the surface-to-atmosphere fluxes of carbon dioxide (CO$_2$) and other important greenhouse gases are changing in response to human influences. These changes need to be quantified to understand climate change and its impacts, but this is difficult to do because natural fluxes occur over large spatial and temporal scales. To infer trends in fluxes and identify phase shifts and amplitude changes in flux seasonal cycles, we construct a flux-inversion system that uses a novel spatially varying time-series decomposition of the fluxes, while also accommodating physical constraints on the fluxes. We incorporate these features into the Wollongong Methodology for Bayesian Assimilation of Trace-gases (WOMBAT, Zammit-Mangion et al., Geosci. Model Dev., 15, 2022), a hierarchical flux-inversion framework that yields posterior distributions for all unknowns in the underlying model. We apply the new method, which we call WOMBAT v2.0, to a mix of satellite observations of CO$_2$ mole fraction from the Orbiting Carbon Observatory-2 (OCO-2) satellite and direct measurements of CO$_2$ mole fraction from a variety of sources. We estimate the changes to CO$_2$ fluxes that occurred from January 2015 to December 2020, and compare our posterior estimates to those from an alternative method based on a bottom-up understanding of the physical processes involved. We find substantial trends in the fluxes, including that tropical ecosystems trended from being a net source to a net sink of CO$_2$ over the study period. We also find that the amplitude of the global seasonal cycle of ecosystem CO$_2$ fluxes increased over the study period by 0.11 PgC/month (an increase of 8%), and that the seasonal cycle of ecosystem CO$_2$ fluxes in the northern temperate and northern boreal regions shifted earlier in the year by 0.4-0.7 and 0.4-0.9 days, respectively (2.5th to 97.5th posterior percentiles).

Hydrofluoroolefins (HFOs) and hydrochlorofluoroolefins (HCFOs) are the leading synthetic replacements for compounds successively banned by the Montreal Protocol and amendments. HFOs and HCFOs readily decompose in the atmosphere to form fluorinated carbonyls, including CF3CHO in yields of up to 100%, which are then photolyzed. A long-standing issue, critical for the transition to safe industrial gases, is whether atmospheric decomposition of CF3CHO yields any quantity of CHF3 (HFC-23), which is one of the most environmentally hazardous greenhouse gases. This comprehensive experimental investigation employs purpose-built photoionization mass spectrometry, Fourier-transform infrared, and microwave spectroscopy techniques and confirms production of CHF3 following excitation at a tropospherically relevant wavelength (lambda = 308 nm) and under atmospheric pressure conditions. Pressure-dependent CHF3 quantum (Phi) and molar (Y) yields are reported from Phi = Y = 0.16 +/- 0.03 under collision-free conditions to Phi = (2.3 +/- 0.3) x 10-4, Y = (1.17 +/- 0.27) x 10-3 at 1 bar N2.

Wildfires can have a significant impact on air quality in Australia during severe burning seasons, but incomplete knowledge of the injection heights of smoke plumes poses a challenge for quantifying smoke exposure. In this study, we use two approaches to quantify the fractions of fire emissions injected above the planetary boundary layer (PBL), and we further investigate the impact of plume injection fractions on daily mean surface concentrations of fine particulate matter (PM2.5) from wildfire smoke in key cities over northern and southeastern Australia from 2009 to 2020. For the first method, we rely on climatological, monthly mean vertical profiles of smoke emissions from the Integrated Monitoring and Modelling System for wildland fires (IS4FIRES) together with assimilated PBL heights from NASA Modern-Era Retrospective Analysis for Research and Application (MERRA) version 2. For the second method, we develop a novel approach based on the Multi-angle Imaging SpectroRadiometer (MISR) observations and a random forest, machine learning model that allows us to directly predict the daily plume injection fractions above the PBL in each grid cell. We apply the resulting plume injection fractions quantified by the two methods to smoke PM2.5 concentrations simulated by the Stochastic Time-Inverted Lagrangian Transport (STILT) model in target cities. We find that characterization of the plume injection heights greatly affects estimates of surface daily smoke PM2.5, especially during severe wildfire seasons, when intense heat from fires can loft smoke high in the troposphere. However, using climatological injection profiles cannot capture well the spatiotemporal variability in plume injection fractions, resulting in a 63 % underestimation of daily fire emission fluxes injected above the PBL in comparison with those fluxes derived from MISR injection fractions. Our random forest model successfully reproduces the daily injected fire emission fluxes against MISR observations (R2=0.88, normalized mean bias = 10 %) and predicts that 27 % and 45 % of total fire emissions rise above the PBL in northern and southeastern Australia, respectively, from 2009 to 2020. Using the plume behavior predicted by the random forest method also leads to better model agreement with observed surface PM2.5 in several key cities near the wildfire source regions, with smoke PM2.5 accounting for 5 %–52 % of total PM2.5 during fire seasons from 2009 to 2020.

The success of chancellery diversity leads is dependent upon how their roles are designed and resourced. This article will provide insights into the design and support of an Equity, Diversity, and Inclusion (EDI) role within the university's chancellery. 66 interviews were conducted with key stakeholders, including chancellery members, EDI officers, and advisory groups, representing diverse Australian and international universities. Thematic analysis identified four crucial themes: achievement measurement, appropriate support and design, lived experience, and warnings. Findings emphasize the significance of appointing a dedicated Deputy Vice-Chancellor (DVC) or senior executive to address EDI matters within the chancellery. Clear Key Performance Indicators and well-defined responsibilities were highlighted for effective governance. Lived experience emerged as a critical factor, promoting normalization and representation of diverse backgrounds. The study cautions against tokenism and stresses collective responsibility for EDI. Recommendations include prioritizing EDI on the strategic agenda, fostering inclusivity, and learning from Indigenous leadership experiences. Embracing these measures can create a more equitable and diverse university environment.

Environmental mercury (Hg) contamination is a global concern requiring action at national scales. Scientific understanding and regulatory policies are underpinned by global extrapolation of Northern Hemisphere Hg data, despite historical, political, and socioeconomic differences between the hemispheres that impact Hg sources and sinks. In this paper, we explore the primary anthropogenic perturbations to Hg emission and mobilization processes that differ between hemispheres and synthesize current understanding of the implications for Hg cycling. In the Southern Hemisphere (SH), lower historical production of Hg and other metals implies lower present-day legacy emissions, but the extent of the difference remains uncertain. More use of fire and higher deforestation rates drive re-mobilization of terrestrial Hg, while also removing vegetation that would otherwise provide a sink for atmospheric Hg. Prevalent Hg use in artisanal and small-scale gold mining is a dominant source of Hg inputs to the environment in tropical regions. Meanwhile, coal-fired power stations continue to be a significant Hg emission source and industrial production of non-ferrous metals is a large and growing contributor. Major uncertainties remain, hindering scientific understanding and effective policy formulation, and we argue for an urgent need to prioritize research activities in under-sampled regions of the SH.

Understanding greenhouse gas–climate processes and feedbacks is a fundamental step in understanding climate variability and its links to greenhouse gas fluxes. Chemical transport models are the primary tool for linking greenhouse gas fluxes to their atmospheric abundances. Hence, accurate simulations of greenhouse gases are essential. Here, we present a new simulation in the GEOS-Chem chemical transport model that couples the two main greenhouse gases—carbon dioxide (CO2) and methane (CH4)—along with the indirect greenhouse gas carbon monoxide (CO) based on their chemistry. Our updates include the online calculation of the chemical production of CO from CH4 and the online production of CO2 from CO, both of which were handled offline in the previous versions of these simulations. In the newly developed coupled (online) simulation, we used consistent hydroxyl radical (OH) fields for all aspects of the simulation, resolving biases introduced by inconsistent OH fields in the currently available uncoupled (offline) CH4, CO and CO2 simulations. We compare our coupled simulation with the existing v12.1.1 GEOS-Chem uncoupled simulations run the way they are currently being used by the community. We discuss differences between the uncoupled and coupled calculation of the chemical terms and compare our results with surface measurements from the NOAA Global Greenhouse Gas Reference Network (NOAA GGGRN), total column measurements from the Total Carbon Column Observing Network (TCCON) and aircraft measurements from the Atmospheric Tomography Mission (ATom). Relative to the standard uncoupled simulations, our coupled results suggest a stronger CO chemical production from CH4, weaker production of CO2 from CO and biases in the OH fields. However, we found a significantly stronger chemical production of CO2 in tropical land regions, especially in the Amazon. The model–measurement differences point to underestimated biomass burning emissions and secondary production for CO. The new self-consistent coupled simulation opens new possibilities when identifying biases in CH4, CO and CO2 source and sink fields, as well as a better understanding of their interannual variability and co-variation.

The use of human-made refrigerants and blowing agents have a long record of restrictions because of the impacts their emissions have had on the atmospheric composition and climate. One of...

Global warming has raised mean surface temperatures by 0.99 ± 0.15 °C from 1850-1900 to 2011-2020. The temperature rise has been greatest in the high latitudes. Alaska has one of the largest temperate and subarctic glaciated areas in the world, which is highly sensitive to climate change. Currently, the mass loss from these glaciers contributes to about a third of the global sea-level rise. For example, the tidewater glacier Columbia Glacier located within Prince William Sound is the largest single contributor to sea level rise through its rapid retreat, which started in the early 1980s. Although internal controls strongly influence the tidewater glacier cycle, the ubiquitous retreat of Alaskan tidewater glaciers indicates climatic forcing is involved. However, it is unlikely climate controls the rate of retreat. There are insufficient meteorological observations from this region to assess the role of climate across a whole tidewater cycle. This project reconstructs the regional climate of southern Alaska from 1836–2015 using dynamical downscaling of the NOAA-CIRES-DOE 20th Century Reanalysis (20CRv3). To do this, the Weather Research and Forecasting model (WRF) has been used to spatially downscale the reanalysis data to produce high-resolution 4 km (convection permitting) output for southcentral/southeastern Alaska. Five different physics parametrisations have been tested for the year 2010. The model output of these five configurations were evaluated using observational records from the Global Surface Summary of the Day (GSOD). The physics scheme that performed most realistically was identified using root mean square error, R squared and normalized mean error for temperature and precipitation. The study shows that 20CRv3 can successfully be downscaled for the study region. As a result, the leading parametrisation was used for a long-term simulation (179 years) to reconstruct local climate and weather over southern Alaska over a significant part of a tidewater glacier cycle. The results will be used to evaluate the influence of climate on these glaciers for the downscaling period from 1836 to 2015.

Model simulations of the fate of trifluoroacetaldehyde, a degradation product of hydrofluoroolefin gases, show that photolysis is the dominant removal pathway, with OH reaction and deposition being relatively minor.

Recent studies demonstrate a short 3–6-month atmospheric lifetime for mercury (Hg). This implies Hg emissions are predominantly deposited within the same hemisphere in which they are emitted, thus placing increasing importance on considering Hg sources, sinks and impacts from a hemispheric perspective. In the absence of comprehensive Hg data from the Southern Hemisphere (SH), estimates and inventories for the SH have been drawn from data collected in the NH, with the assumption that the NH data are broadly applicable. In this paper, we centre the uniqueness of the SH in the context of natural biogeochemical Hg cycling, with focus on the midlatitudes and tropics. Due to its uniqueness, Antarctica warrants an exclusive review of its contribution to the biogeochemical cycling of Hg and is therefore excluded from this review. We identify and describe five key natural differences between the hemispheres that affect the biogeochemical cycling of Hg: biome heterogeneity, vegetation type, ocean area, methylation hotspot zones and occurence of volcanic activities. We review the current state of knowledge of SH Hg cycling within the context of each difference, as well as the key gaps that impede our understanding of natural Hg cycling in the SH. The differences demonstrate the limitations in using NH data to infer Hg processes and emissions in the SH.

WOMBAT (the WOllongong Methodology for Bayesian Assimilation of Trace-gases) is a fully Bayesian hierarchical statistical framework for flux inversion of trace gases from flask, in situ, and remotely sensed data. WOMBAT extends the conventional Bayesian synthesis framework through the consideration of a correlated error term, the capacity for online bias correction, and the provision of uncertainty quantification on all unknowns that appear in the Bayesian statistical model. We show, in an observing system simulation experiment (OSSE), that these extensions are crucial when the data are indeed biased and have errors that are spatio-temporally correlated. Using the GEOS-Chem atmospheric transport model, we show that WOMBAT is able to obtain posterior means and variances on non-fossil-fuel CO2 fluxes from Orbiting Carbon Observatory-2 (OCO-2) data that are comparable to those from the Model Intercomparison Project (MIP) reported in Crowell et al. (2019). We also find that WOMBAT's predictions of out-of-sample retrievals obtained from the Total Column Carbon Observing Network (TCCON) are, for the most part, more accurate than those made by the MIP participants.

Australian fires are a primary driver of variability in Australian atmospheric composition and contribute significantly to regional and global carbon budgets. However, biomass burning emissions from Australia remain highly uncertain. In this work, we use surface in situ, ground‐based total column and satellite total column observations to evaluate the ability of two global models (GEOS‐Chem and ACCESS‐UKCA) and three global biomass burning emission inventories (FINN1.5, GFED4s, and QFED2.4) to simulate carbon monoxide (CO) in the Australian atmosphere. We find that emissions from northern Australia savanna fires are substantially lower in FINN1.5 than in the other inventories. Model simulations driven by FINN1.5 are unable to reproduce either the magnitude or the variability of observed CO in northern Australia. The remaining two inventories perform similarly in reproducing the observed variability, although the larger emissions in QFED2.4 combined with an existing high bias in the southern hemisphere background lead to large CO biases. We therefore recommend GFED4s as the best option of the three for global modeling studies with focus on Australia or the Southern Hemisphere. Near fresh fire emissions, the higher resolution ACCESS‐UKCA model is better able to simulate surface CO than GEOS‐Chem, while GEOS‐Chem captures more of the observed variability in the total column and remote surface air measurements. We also show that existing observations in Australia can only partially constrain global model estimates of biomass burning. Continuous measurements in fire‐prone parts of Australia are needed, along with updates to global biomass burning inventories that are validated with Australian data.

For a vertical profile comparison of the molecular hydrogen (H 2 ) we used the records from the Aircraft (AIA) flask s ampling d ata f rom K rummel e t a l., 2 021r m easured o ver T asmania.T he s easonal a verage r atios o f the H 2 measured at varying heights with respect to the ground values (from 1991 to 2000) were plotted against the average model estimates from 2015 and 2016 (see Figure S7).SON and DJF were the seasons for which GEOS-Chem represented best the evolution of H 2 with altitude.On the other hand, for MAM and JJA, the model was unable to capture the vertical gradient of the observations attributing more H 2 in height than the reported in the average nine year trend.This might be caused by enhanced modelled vertical transport of H 2 .

This commentary paper from the recently formed International Global Atmospheric Chemistry (IGAC) Southern Hemisphere Working Group outlines key issues in atmospheric composition research that particularly impact the Southern Hemisphere. In this article, we present a broad overview of many of the challenges for understanding atmospheric chemistry in the Southern Hemisphere, before focusing in on the most significant factors that differentiate it from the Northern Hemisphere. We present sections on the importance of biogenic emissions and fires in the Southern Hemisphere, showing that these emissions often dominate over anthropogenic emissions in many regions. We then describe how these and other factors influence air quality in different parts of the Southern Hemisphere. Finally, we describe the key role of the Southern Ocean in influencing atmospheric chemistry and conclude with a description of the aims and scope of the newly formed IGAC Southern Hemisphere Working Group.