Chelsea R. Thompson

Most global atmospheric chemistry models represent ≥C₄ alkanes using lumped surrogates, limiting both detailed simulation of their oxygenated products and evaluation against comprehensive observational datasets. We present MOZART-T3, which replaces the lumped BIGALK representation with a more explicit treatment of individual C₄−C₆ alkane species and resolves propane peroxy radical isomers, enabling more mechanistically consistent alkane chemistry in the Community Atmosphere Model with chemistry (CAM-chem). Global simulations demonstrate that T3 maintains similar total alkane burdens compared to previous mechanisms, while substantially altering oxygenated product budgets and distributions. Relative to MOZART-T1, T3 significantly reduces the global burden of methyl ethyl ketone (MEK) primarily through incorporation of more comprehensive n-butane oxidation chemistry, with additional contributions from increased photolysis rates and updated emission speciation. T3 introduces six additional C₅−C₆ ketone species that contribute ∼40% to global ketone sources but only ∼2% to the total burden due to their short lifetimes. The acetaldehyde burden decreases by 8−14% through compound-specific yields that replace the fixed yield in previous mechanisms. The choice of anthropogenic emission inventory drives larger variations in alkane burdens (∼24%) than does mechanism complexity (∼4%), but mechanism choice dominates for oxidation products. T3 enables evaluation of previously unrepresented species including individual alkanes, propanal, and peroxypropionyl nitrate, with generally improved simulation of oxygenated compounds, although the evaluation results vary temporally and spatially. While lumped approaches sufficiently represent global-scale major pollutant concentrations, T3’s detailed treatment enables more comprehensive evaluation and is expected to be more important for urban air quality applications using higher-resolution regional simulations.

Most global atmospheric chemistry models represent ≥C₄ alkanes using lumped surrogates, limiting both detailed simulation of their oxygenated products and evaluation against comprehensive observational datasets. We present MOZART-T3, which replaces the lumped BIGALK representation with a more explicit treatment of individual C₄−C₆ alkane species and resolves propane peroxy radical isomers, enabling more mechanistically consistent alkane chemistry in the Community Atmosphere Model with chemistry (CAM-chem). Global simulations demonstrate that T3 maintains similar total alkane burdens compared to previous mechanisms, while substantially altering oxygenated product budgets and distributions. Relative to MOZART-T1, T3 significantly reduces the global burden of methyl ethyl ketone (MEK) primarily through incorporation of more comprehensive n-butane oxidation chemistry, with additional contributions from increased photolysis rates and updated emission speciation. T3 introduces six additional C₅−C₆ ketone species that contribute ∼40% to global ketone sources but only ∼2% to the total burden due to their short lifetimes. The acetaldehyde burden decreases by 8−14% through compound-specific yields that replace the fixed yield in previous mechanisms. The choice of anthropogenic emission inventory drives larger variations in alkane burdens (∼24%) than does mechanism complexity (∼4%), but mechanism choice dominates for oxidation products. T3 enables evaluation of previously unrepresented species including individual alkanes, propanal, and peroxypropionyl nitrate, with generally improved simulation of oxygenated compounds, although the evaluation results vary temporally and spatially. While lumped approaches sufficiently represent global-scale major pollutant concentrations, T3’s detailed treatment enables more comprehensive evaluation and is expected to be more important for urban air quality applications using higher-resolution regional simulations.

Biomass burning (BB) is a major global sources of ozone (O ₃ ) precursors, including nitrogen oxides (NO _x ), carbon monoxide (CO), and volatile organic compounds (VOCs). Here, we combine Community Earth System Model 1 with airborne measurements from the NASA Atmospheric Tomography mission conducted during 2016–2018 to assess the global impact of aged BB emissions on O ₃ from the surface to the lower stratosphere. The model captures the broad spatial distribution of BB‐related tracers and O ₃ in the Atlantic, but it significantly underestimates BB‐related aerosol concentrations by an order of magnitude above 3 km in the tropical and Northern Hemispheric Pacific, leading to an underestimation of BB‐induced O ₃ concentrations. In the upper troposphere and lower stratosphere over the tropical Atlantic, BB‐induced O ₃ enhancements are most pronounced during August to November, with peak values reaching up to 30 ppbv in October. These enhancements are primarily driven by the oxidation of BB‐emitted VOCs and CO, followed by the photolysis of the NO ₂ . The Asian summer monsoon circulation plays a crucial role in lofting these precursors into higher altitudes, where NO _x is converted into its reservoir form, peroxyacetyl nitrate. These findings demonstrate BB's extensive vertical and horizontal influence on atmospheric O ₃ , underscoring the importance of accurately representing BB processes in climate and air quality models to better assess their impacts on global air pollution and climate change.

Most global atmospheric chemistry models represent ≥C₄ alkanes using lumped surrogates, limiting both detailed simulation of their oxygenated products and evaluation against comprehensive observational datasets. We present MOZART-T3, which replaces the lumped BIGALK representation with a more explicit treatment of individual C₄−C₆ alkane species and resolves propane peroxy radical isomers, enabling more mechanistically consistent alkane chemistry in the Community Atmosphere Model with chemistry (CAM-chem). Global simulations demonstrate that T3 maintains similar total alkane burdens compared to previous mechanisms, while substantially altering oxygenated product budgets and distributions. Relative to MOZART-T1, T3 significantly reduces the global burden of methyl ethyl ketone (MEK) primarily through incorporation of more comprehensive n-butane oxidation chemistry, with additional contributions from increased photolysis rates and updated emission speciation. T3 introduces six additional C₅−C₆ ketone species that contribute ∼40% to global ketone sources but only ∼2% to the total burden due to their short lifetimes. The acetaldehyde burden decreases by 8−14% through compound-specific yields that replace the fixed yield in previous mechanisms. The choice of anthropogenic emission inventory drives larger variations in alkane burdens (∼24%) than does mechanism complexity (∼4%), but mechanism choice dominates for oxidation products. T3 enables evaluation of previously unrepresented species including individual alkanes, propanal, and peroxypropionyl nitrate, with generally improved simulation of oxygenated compounds, although the evaluation results vary temporally and spatially. While lumped approaches sufficiently represent global-scale major pollutant concentrations, T3’s detailed treatment enables more comprehensive evaluation and is expected to be more important for urban air quality applications using higher-resolution regional simulations.

Tropospheric ozone over the South and Tropical Atlantic plays an important role in the photochemistry and energy budget of the atmosphere. In this remote region, tropospheric ozone estimates from reanalysis datasets show the largest discrepancies. The present study characterises the vertical and horizontal distribution of tropospheric ozone over the South and Tropical Atlantic during February and October 2017 using a multispectral synergism called IASI + GOME2, two global chemistry reanalysis products – the Copernicus Atmosphere Monitoring Service reanalysis (CAMS reanalysis) and the Tropospheric Chemistry Reanalysis version 2 (TCR-2) – and in situ airborne measurements from the Atmospheric Tomography Mission (ATom). In February, biomass burning in West and Central Africa and deep convection over the Gulf of Guinea strongly influence the region. IASI + GOME2 captures enhanced ozone abundances in the Southern Hemisphere and low ozone concentrations in the Northern Hemisphere, exhibiting excellent agreement with ATom-2 profiles. In contrast, both reanalyses underestimate lower-tropospheric ozone influenced by biomass-burning outflow and overestimate ozone in the Northern Hemisphere due to excessive contributions from stratospheric intrusion and North American anthropogenic emissions. In October, tropospheric ozone enhancement associated with biomass-burning outflow from Austral Africa is consistently depicted by observations and reanalyses. These results emphasize the need to evaluate the seasonal variability of each of the multiple sources of ozone precursors within atmospheric chemistry reanalyses.

The Montreal Protocol on Substances that Deplete the Ozone Layer requires that the production of long-lived ozone-depleting substances (ODSs) that are intended for use in emissive applications be phased out. The Protocol does not, however, limit the release to the atmosphere of ODSs already existing in such applications and equipment. Accounting for emissions from these “banked” ODSs (e.g., in insulating foams) is important for monitoring the success of and compliance with the Protocol, for understanding where further mitigation of ODS emissions might be effective, and for estimating future ozone depletion. Here, we present a new bottom-up model that incorporates existing use and life-cycle information to calculate emissions and banks as well as uncertainties in the quantities. To demonstrate the model, we apply it to 1,1-dichloro-1-fluoroethane (HCFC-141b), a chemical used primarily in foam insulation and whose production is currently being phased out. We calculate global emission trends that are qualitatively similar to those derived from atmospheric measurements from 1990 to 2017. After 2017, our calculated emissions no longer track the observationally based trends through the end of the comparison in 2021. This discrepancy suggests either a growing additional source of emissions that is inconsistent with reported production or a model deficiency that was not apparent before 2017. Our calculations also show that the easily recoverable portion of the bank will be smaller in the future than the total bank estimated in other recent work, with implications for the feasibility of recovering banks before the release of HCFC-141b to the atmosphere.

Nitric oxide (NO) in the remote marine atmosphere is underestimated by chemistry‐climate models. We explore the potential oceanic emissions of NO and its impacts using a global chemistry‐climate model with a newly developed oceanic NO emission inventory, considering the abiotic photochemical production of NO in the seawater. The results are evaluated using global observations from the NASA Atmospheric Tomography Mission (ATom). We propose that the photochemical production of NO from the photolysis of dissolved inorganic nitrite and nitrate in the surface seawater could lead to an oceanic NO _x source of ∼3 Tg N per year, which could explain the missing NO in the remote marine boundary layer. This potential oceanic NO source leads to a small but potentially widespread increase in surface ozone and hydroxyl radicals in the remote marine environment, altering our understanding of the role the remote marine atmosphere plays in the global system. Further, the role of the photolysis of nitrate aerosols may be overestimated in recent studies and warrants further investigation.

Studying tropospheric ozone over the remote areas of the planet, such as the open oceans and the polar regions, is crucial to understand the role of ozone as a global climate forcer and regulator of atmospheric oxidative capacity. A focus on the pristine oceanic and polar regions complements the available land-based datasets and provides insights into key photochemical and depositional loss processes that control the concentrations and spatiotemporal variability in ozone as well as the physicochemical mechanisms driving these patterns. However, an assessment of the role of ozone over the oceanic and polar regions has been hampered by a lack of comprehensive observational datasets. Here, we present the first comprehensive collection of ozone data over the oceans and the polar regions. The overall dataset consists of 77 ship cruises/buoy-based observations and 48 aircraft-based campaigns. The dataset, consisting of more than 630 000 independent ozone measurement data points covering the period from 1977 to 2022 and an altitude range from the surface to 5000 m (with a focus on the lowest 2000 m), allows systematic analyses of the spatiotemporal distribution and long-term trends over the 11 defined ocean/polar regions. The datasets from ships, buoys, and aircraft are complemented by ozonesonde data from 29 launch sites or field campaigns and by 21 non-polar and 17 polar ground-based station datasets. The datasets contain information on how long the observed air masses were isolated from land, as estimated by backward trajectories from the individual observation points. To extract observations representative of oceanic conditions, we recommend using a subset of the data with an isolation time of 72 h or longer, from the analysis with coincident radon observations. These filtered oceanic and polar data showed typically flat diurnal cycles at high latitudes, whereas daytime decreases in ozone (11 %–16 %) were observed at lower latitudes. The ship/buoy- and aircraft-based datasets presented here will supplement the land-based ones in the TOAR-II (Tropospheric Ozone Assessment Report Phase II) database to provide a fully global assessment of tropospheric ozone. The described dataset is available at https://doi.org/10.17596/0004044 (Kanaya et al., 2025).