We developed a multi-air-pollutant inversion system to estimate non-methane volatile organic compound (NMVOC) emissions using TROPOMI formaldehyde retrievals. We found that the inversion significantly improved formaldehyde simulations and reduced NMVOC emission uncertainties. The optimized NMVOC emissions effectively corrected the overestimation of O₃ levels, mainly by decreasing the rate of the RO₂ + NO reaction and increasing the rate of the NO₂ + OH reaction.

From aircraft measurements in the upper troposphere/lower stratosphere, we find a correlation between the ozone and particulate sulfate in the lower stratosphere. The correlation exhibits some variability over the measurement period exceeding the background sulfate-to-ozone correlation. From our analysis, we conclude that gas-to-particle conversion of volcanic sulfur dioxide leads to observed enhanced sulfate aerosol mixing ratios.

Using observations of the Sentinel-5P satellite and the latest version of the inversion algorithm DECSO, anthropogenic NO_x emissions are derived for Europe for the years 2019–2022 with a spatial resolution of 0.2°. The results are compared with European emissions of the Copernicus Atmosphere Monitoring Service.

Arctic lidar data for 1 year are compared with global modeling of aerosol tracers in the stratosphere. A trend in the aerosol backscatter can be found. These observations are further compared with a model study to investigate the aerosol origin of the observed arctic aerosol. We found a correlation with increased backscatter signal during summer and early autumn and pathways from the Southeast Asian monsoon region and remains of the Asian tropopause aerosol layer in the Arctic.

The supercooled liquid fraction (SLF) in mixed-phase clouds is retrieved for the first time using passive geostationary satellite observations based on differences in liquid droplet and ice particle radiative properties. The retrieved results are comparable to global distributions observed by active instruments, and the feasibility of the retrieval method to analyze the observed trends of the SLF has been validated.

The present research unveiled that acidity dominates while transition metal ions harmonize with the light absorption properties of humic-like substances (HULIS). Cu²⁺ has quenching effects on HULIS by complexation, hydrogen substitution, or electrostatic adsorption, with aromatic structures of HULIS. Such effects are less pronounced if from Mn²⁺, Ni²⁺, Zn²⁺, and Cu²⁺. Oxidized HULIS might contain electron-donating groups, whereas N-containing compounds might contain electron-withdrawing groups.

In situ airborne observations of ongoing tropopause-overshooting convection and an above-anvil cirrus plume from the 31 May 2022 flight of the Dynamics and Chemistry of the Summer Stratosphere (DCOTSS) field campaign are examined. Upper troposphere and lower stratosphere composition changes are evaluated along with possible contributing dynamical and physical processes. Measurements reveal multiple changes in air mass composition and stratospheric hydration throughout the flight.

Large quantities of CO and CO₂ are emitted during conventional steel production. As satellite-based estimates of CO₂ emissions at the facility level are challenging, co-emitted CO can indicate the carbon footprint of steel plants. We estimate CO emissions for German steelworks and use CO₂ emissions from emissions trading data to derive a sector-specific CO/CO₂ emission ratio for the steel industry; it is a prerequisite to use CO as a proxy for CO₂ emissions from similar steel production sites.

A three-stage model was developed to obtain the global maps of reactive nitrogen components during 2000–2100. The results implied that cross-validation R² values of four species showed satisfactory performance (R² > 0.55). Most reactive nitrogen components, except NH_3, in China showed increases during 2000–2013. In the future scenarios, SSP3-7.0 (traditional-energy scenario) and SSP1-2.6 (carbon neutrality scenario) showed the highest and lowest reactive nitrogen component concentrations.

During the summer in Catalonia, a cool wind, the marinada, blows into the eastern Ebro basin in the afternoon. This study investigates its previously unclear dynamics using observations and a meteorological model. It is found to be driven by a cool marine air mass that flows over the mountains into the basin. The study shows how the sea breeze, upslope winds, larger weather patterns and irrigation play a prominent role in the formation and characteristics of the marinada.

Nitrogen oxides (NO_x = NO + NO₂) are important air pollutants. This study addresses the challenge of accurately estimating NO_x emissions from NO₂ satellite observations. We develop a realistic model to convert NO₂ to NO_x by using simulated plumes from various power plants. We apply the model to satellite NO₂ observations, significantly reducing biases in estimated NO_x emissions. The study highlights the potential for a consistent, high-resolution estimation of NO_x emissions using satellite data.

The chemical composition of atmospheric particles has shown significant changes in recent years. We investigated the potential effects of changes in inorganics on aerosol water uptake and, thus, secondary organic aerosol formation in wintertime haze based on the size-resolved measurements of non-refractory fine particulate matter (NR-PM_2.5) in Xi’an, northwestern China. We highlight the key role of aerosol water as a medium to link inorganics and organics in their multiphase processes.

Atmospheric volatile organic compounds (VOCs) constitute many species, acting as precursors to ozone and aerosol. Given the uncertainties in VOC emissions, lack of evaluation studies, and recent changes in emissions, this work adapts the EMEP MSC-W to evaluate emission inventories in Europe. We focus on the varying agreement between modelled and measured VOCs across different species and underscore potential inaccuracies in total and sector-specific emission estimates.

Ice formation by particles is an important way of making mixed-phase and ice clouds. We found that particles collected in the marine atmosphere exhibit diverse ice nucleation abilities and mixing states. Sea salt mixed-sulfate particles were enriched in ice-nucleating particles. Selective aging on sea salt particles made particle populations more externally mixed. Characterizations of particles and their mixing state are needed for a better understanding of aerosol–cloud interactions.

In this study, we found that biomass burning (31.0 %) and coal combustion (31.1 %) were the dominant sources of water-insoluble organic carbon in China, with coal combustion sources exhibiting the strongest light-absorbing capacity. Additionally, we propose a light-absorbing carbonaceous continuum, revealing that components enriched with fossil sources tend to have stronger light-absorbing capacity, higher aromaticity, higher molecular weights, and greater recalcitrance in the atmosphere.

This study investigates long-term trends of criteria air pollutants, including NO₂, CO, SO₂, O₃ and PM_2.5, and NO₂+O₃ measured in 10 Canadian cities during the last 2 to 3 decades.  We also investigate associated driving forces in terms of emission reductions, perturbations from varying weather conditions and large-scale wildfires, as well as changes in O₃ sources and sinks.

In contrast with past work showing that the reduction of emissions was the dominant factor for the nationwide increase of surface O₃ during the lockdown in China, this study finds that the variation in meteorology (temperature and other parameters) plays a more important role. This result is obtained through sensitivity simulations using a chemical transport model constrained by satellite (TROPOMI) data and calibrated with surface observations.

A state-of-the-art thermodynamic model has been coupled with the city-scale chemistry transport model EPISODE–CityChem to investigate the equilibrium between the inorganic gas and aerosol phases over the greater Athens area, Greece. The simulations indicate that the formation of nitrates in an urban environment is significantly affected by local nitrogen oxide emissions, as well as ambient temperature, relative humidity, photochemical activity, and the presence of non-volatile cations.

Effective radiative forcing (ERF) is a metric for estimating how human activities and natural agents change the energy flow into and out of the Earth’s climate system. We investigate the anthropogenic aerosol ERF, and we estimate the contribution of individual processes to the total ERF using simulations from Earth system models within the Coupled Model Intercomparison Project Phase 6 (CMIP6). Our findings highlight that aerosol–cloud interactions drive ERF variability during the last 150 years.

A climatology of the major variables and terms of the transformed Eulerian-mean (TEM) momentum and thermodynamic equations from four global atmospheric reanalyses is evaluated. The spread among reanalysis TEM momentum balance terms is around 10 % in Northern Hemisphere winter and up to 50 % in Southern Hemisphere winter. The largest uncertainties in the thermodynamic equation (about 50 %) are in the vertical advection, which does not show a structure consistent with the differences in heating.

Better characterizing the relationship between sea ice and clouds is key to understanding Arctic climate because clouds and sea ice affect surface radiation and modulate Arctic surface warming. Our results indicate that Arctic liquid clouds robustly increase in response to sea ice decrease. This increase has a cooling effect on the surface because more solar radiation is reflected back to space, and it should contribute to dampening future Arctic surface warming.

We try to improve the forecast of ice supersaturation (ISS) and potential persistent contrails using data on dynamical quantities in addition to temperature and relative humidity in a modern kind of regression model. Although the results are improved, they are not good enough for flight routing. The origin of the problem is the strong overlap of probability densities conditioned on cases with and without ice-supersaturated regions (ISSRs) in the important range of 70–100 %.

In the Observed Composition Trends And Variability in the UTLS (OCTAV-UTLS) Stratosphere-troposphere Processes And their Role in Climate (SPARC) activity, we have mapped multiplatform ozone datasets into coordinate systems to systematically evaluate the influence of these coordinates on binned climatological variability. This effort unifies the work of studies that focused on individual coordinate system variability. Our goal was to create the most comprehensive assessment of this topic.

The formation and evolution mechanisms of aromatics-derived highly oxygenated organic molecules (HOMs) are essential to understand the formation of secondary organic aerosol pollution. Our conclusion highlights an underappreciated formation pathway of aromatics-derived HOMs and elucidates detailed formation mechanisms of certain HOMs, which advances our understanding of HOMs and potentially explains the existing gap between model prediction and ambient measurement of the HOMs' concentrations.

The springtime southeast Atlantic atmosphere contains lots of smoke from continental fires. This smoke travels with water vapor; more smoke means more humidity. We use aircraft observations and models to describe how the values change through the season and over the region. We sort the atmosphere into different types by vertical structure and amount of smoke and humidity. Since our work shows how frequently these components coincide, it helps to better quantify heating effects over this region.

To support the interpretation of the data collected during the HALO-(AC)³ campaign, which took place in the North Atlantic sector of the Arctic from 7 March to 12 April 2022, we analyze how unusual the weather and sea ice conditions were with respect to the long-term climatology. From observations and ERA5 reanalysis, we found record-breaking warm air intrusions and a large variety of marine cold air outbreaks. Sea ice concentration was mostly within the climatological interquartile range.

During the 2020 austral summer, the pristine atmosphere of the southwest Indian Ocean basin experienced significant perturbations. Numerical models indicated that the lower-stratospheric aerosol content was influenced by the intense and persistent stratospheric aerosol layer generated during the 2019–2020 extreme Australian bushfire events. Ground-based observations at Réunion confirmed the simultaneous presence of African and Australian aerosol layers.

To understand how changing emissions have impacted aerosols in remote regions, we measured nitrate and sulfate in Barbados and compared them to model predictions from EPA’s Air QUAlity TimE Series (EQUATES). Nitrate was stable, except for spikes in 2008 and 2010 due to transported smoke. Sulfate decreased in the 1990s due to reductions in sulfur dioxide (SO₂) in the US and Europe; then it increased in the 2000s, likely due to anthropogenic emissions from Africa.