The impact of aerosols on Earth's radiation budget and human health is important and strongly depends on their composition. One desire of our scientific community is to derive the composition of the aerosol from satellite sensors. However, satellites observe aerosol optical properties (and not aerosol composition) based on remote sensing instrumentation. This study assesses how much aerosol optical properties can tell us about aerosol composition.

We use the GEOS-Chem model with additional anthropogenic and biomass burning chlorine emissions combined with updated parameterizations for N₂O₅ ＋ Cl chemistry to investigate the impacts of chlorine chemistry on air quality in China. Our study not only significantly improves the model's performance but also demonstrates the importance of non-sea-salt chlorine sources as well as an appropriate parameterization for N₂O₅ ＋ Cl chemistry to the impact of chlorine chemistry in China.

Mineral dust or similar ice-nucleating particles (INPs) are needed to initiate cloud droplet freezing at temperatures common in shallow clouds. In this work we examine how INPs that are released from the sea surface impact marine clouds. Our high-resolution simulations show that turbulent updraughts carry these particles effectively up to the clouds, where they initiate cloud droplet freezing. Sea surface INP emissions become more important with decreasing background dust INP concentrations.

Collision–coagulation of small droplets in turbulent clouds leads to the production of rain. Turbulence causes droplet clustering and higher relative droplet velocities, and these should enhance the collision–coagulation rate. We find, surprisingly, that collision–coagulation starkly diminishes clustering and strongly alters relative velocities. We provide a theory that explains this result. Our results call for a new perspective on how we understand particle/droplet collision in clouds.

We investigate causes of a poor-air-quality episode in northern Europe in October 2020 during which EU health limits for air quality were vastly exceeded. Such episodes may trigger measures to improve air quality. Analysis based on satellite observations, transport simulations, and surface observations revealed two sources of pollution. Emissions of mineral dust in Central Asia and biomass burning in Ukraine arrived almost simultaneously in Norway, and transport continued into the Arctic.

A novel probabilistic approach is proposed to evaluate relative humidity (RH) profiles simulated by an atmospheric model with respect to satellite-based RH defined from probability distributions. It improves upon deterministic comparisons by enhancing the information content to enable a finer assessment of each model–observation discrepancy, highlighting significant departures within a deterministic confidence range. Geographical and vertical distributions of the model biases are discussed.

As a poison in the air that we breathe and the food that we eat, mercury is a human health concern for society as a whole. In that regard, this work deals with monitoring and modelling mercury in the environment, improving wherewithal, identifying the strength of the different components at play, and interpreting information to support the efforts that seek to safeguard public health.

Highly polluted air flows from the surface to higher levels of the atmosphere during the Asian summer monsoon. At high levels, the air is trapped within eddies. Here, we study how air masses can leave the eddy within its cutoff, how they distribute, and how their chemical composition changes. We found evidence for transport from the eddy to higher latitudes over the North Pacific and even Alaska. During transport, trace gas concentrations within cutoffs changed gradually, showing steady mixing.

This study finds a new phenomenon of weak wind deepening (WWD) associated with the peripheral circulation of typhoon and gives the influence mechanism of WWD on its contribution to daily variation during sustained ozone episodes. The WWD provides the premise for pollution accumulation in the whole PBL and continued enhancement of ground-level ozone via vertical mixing processes. These findings could benefit the daily daytime ozone forecast in the PRD region and other areas.

We analyzed the observational data and used models to discover the impact of the total ozone column (TOC) on the occurrence of tropospheric ozone depletion events (ODE) in the Antarctic. The results suggest that the decrease of TOC favors the occurrence of ODE. When TOC varies the rates of major ODE accelerating reactions are substantially altered but the rates of major ODE decelerating reactions remain unchanged. As a result, the occurrence of ODE negatively depends on the TOC.

On-road emissions are thought to vary widely from existing predictions, as the effects of the age of the vehicle fleet, the performance of emission control systems, and variations in speed are difficult to assess under ambient driving conditions. We present an observational approach to characterize on-road emissions and show that the method is consistent with other approaches to within ~ 3 %.

Aerosols are liquid or solid particles suspended in the air that can interact with radiation and clouds, modifying the meteoclimatic conditions. Using an atmospheric model, we study the climatological impact of aerosols through their effects on clouds in the Alps, a region characterized by high pollution levels in the densely populated surrounding flatlands. Results show that cloud cover, temperature, and precipitation are affected by aerosols, and the response varies with elevation and season.

Quantifying methane emissions from different sources is a key focus of current research. We present a method for estimating sectoral methane emissions that uses ethane as a tracer for fossil fuel methane. By incorporating variable ethane : methane emission ratios into this model, we produce emissions estimates with improved uncertainty characterisation. This method will be particularly useful for studying methane emissions in areas with complex distributions of sources.

This study reports pollen observations at four lidar stations (Hohenpeißenberg, Germany; Kuopio, Finland; Leipzig, Germany; and Warsaw, Poland) during the intensive observation campaign organized in May 2020. A novel simple method for the characterization of the pure pollen is proposed, based on lidar measurements. It was applied to evaluate the pollen depolarization ratio and for the aerosol classifications.

The evidence of the effects of atmospheric pollution (and particularly fine particulate matter, PM_2.5) on human mortality is now unquestionable. Here, 895 000 annual premature deaths (PD) are estimated for the present (1991–2010), which increases to 1 540 000 in the year 2050 due to the ageing of the European population. The implementation of a mitigation scenario (80 % of the energy production in Europe from renewable sources) could lead to a decrease of over 60 000 annual PD for the year 2050.

Large amounts of wildfire smoke reached the stratosphere in 2017. The literature on stratospheric aerosol is mainly based on horizontally viewing sensors that saturate in dense smoke. Using also a vertically viewing sensor with orders of magnitude shorter path in the smoke, we show that the horizontally viewing sensors miss a dramatic exponential decline of the aerosol load with a half-life of 10 d, where 80 %–90 % of smoke is lost. We attribute the decline to photolytic loss of organic aerosol.

We present the hygroscopicity of 23 organic species with different physicochemical properties using a hygroscopicity tandem differential mobility analyzer (HTDMA) and compare the results with previous studies. Based on the hygroscopicity parameter κ, the influence of different physicochemical properties that potentially drive hygroscopicity, such as the functionality, water solubility, molar volume, and O : C ratio of organics, are examined separately.

We have undertaken atmospheric iodine monoxide (IO) observations in the global marine boundary layer with a wide latitudinal coverage and sea surface temperature (SST) range. We conclude that atmospheric iodine is abundant over the Western Pacific warm pool, appearing as an iodine fountain, where ozone (O₃) minima occur. Our study also found negative correlations between IO and O₃ concentrations over IO maxima, which requires reconsideration of the initiation process of halogen activation.

We present an intercomparison of 2009–2018 lapse rate tropopause characteristics as derived from ECMWF's ERA5 and ERA-Interim reanalyses. Large-scale features are similar, but ERA5 shows notably larger variability, which we mainly attribute to UTLS temperature fluctuations due to gravity waves being better resolved by ECMWF's IFS forecast model. Following evaluation with radiosondes and GPS data, we conclude ERA5 will be a more suitable asset for tropopause-related studies in future work.

We present a thorough investigation of an anomalous transport of mineral dust over a region renowned for excess airborne particulate matter, the Italian Po Valley, which occurred in late March 2021. Both the origin of this dust outbreak, which was localized in central Asia (i.e., the so-called Aralkum Desert), and the upstream synoptic conditions, investigated here in extreme detail using multiple integrated observations including in situ measurements and remote sensing, were atypical.

Forest fires emit carbon monoxide (CO) that can be transported into the atmosphere far from the sources and reacts to produce ozone (O₃) that affects climate, ecosystems and health. O₃ is also produced in the stratosphere and can be transported downwards. Using a global numerical model, we found that forest fires can affect CO and O₃ even in the South Pacific, the most pristine region of the global ocean, but transport from the stratosphere is a more important O₃ source than fires in the region.

Aerosols can influence O₃ through aerosol–radiation interactions, including aerosol–photolysis interaction (API) and aerosol–radiation feedback (ARF). The weakened photolysis rates and changed meteorological conditions reduce surface-layer O₃ concentrations by up to 9.3–11.4 ppb, with API and ARF contributing 74.6 %–90.0 % and 10.0 %–25.4 % of the O₃ decrease in three episodes, respectively, which indicates that API is the dominant way for O₃ reduction related to aerosol–radiation interactions.

From thorough measurements of numerous oxygenated volatile organic compounds, we show that their photodissociation can be important for radical production and ozone formation in the atmosphere. This effect was underestimated in previous studies, as measurements of them were lacking.

Nanometer- to micrometer-sized particles in the atmosphere, namely aerosols, play a crucial role in cloud formation as cloud droplets form on aerosols. This study uses a weather forecasting model to examine the impacts of a large emission of aerosol particles from biomass burning activities over Southeast Asia. We find that additional cloud droplets brought by fire-emitted particles can lead to taller and more reflective convective clouds with increased rainfall.

Aerosol water uptake plays a key role in atmospheric physicochemical processes. We designed chamber experiments on aerosol water uptake of secondary organic aerosol (SOA) from mixed biogenic and anthropogenic precursors with inorganic seed. Our results highlight this chemical composition influences the reconciliation of the sub- and super-saturated water uptake, providing laboratory evidence for understanding the chemical controls of water uptake of the multi-component aerosol.

In this study, we quantity the long-term variabilities and the underlying drivers of NO₂ from 2005 to 2020 over the Yangtze River Delta (YRD), one of the most densely populated and highly industrialized city clusters in China. We reveal the significant effect of the Action Plan on the Prevention and Control of Air Pollution since 2013 adopted by the Chinese government to reduce NO_x pollution. Our study can improve the understanding of pollution control measures on a regional scale.

This study uses a model developped at LATMOS (France) to analyze the behavior of the Antarctic polar vortex from 1979 to 2020 at 675 K, 550 K, and 475 K isentropic levels. We found that the vortex edge intensity is stronger during the September–October–November period, while its edge position is less extended during this period. The polar vortex is stronger and lasts longer during solar minimum years. Breakup dates of the polar vortex are linked to the ozone hole and maximum wind speed.

The COVID-19 lockdown had a large impact on anthropogenic emissions and particularly on nitrogen dioxide (NO₂). A new method of isolation of background, urban, and industrial components in NO₂ is applied to estimate the lockdown impact on each of them. From 16 March to 15 June 2020, urban NO₂ declined by −18 % to −28 % in most regions of the world, while background NO₂ typically declined by less than −10 %.

Heterogeneous oxidation of SO₂ is suggested to be one of the most important pathways for sulfate formation during extreme haze events in China, yet the exact mechanism remains highly uncertain. Our study reveals that ubiquitous compounds at the sea surface PAHS and DMSO, when exposed to SO₂ under simulated sunlight irradiation, generate abundant organic sulfur compounds, providing implications for air-sea interaction and secondary organic aerosols formation processes.

Smoke plumes are chemically complex. This work combines airborne observations of smoke plume composition with a photochemical model to probe the production of ozone and the fate of reactive gases in the outflow of a large wildfire. Model–measurement comparisons illustrate how uncertain emissions and chemical processes propagate into simulated chemical evolution. Results provide insight into how this system responds to perturbations, which can help guide future observation and modeling efforts.