This study provides a holistic approach to studying the spectrally resolved light absorption by atmospheric brown carbon (BrC) and black carbon using long time series of daily samples from filter-based measurements. The obtained results provide (1) a better understanding of the aerosol absorption profile and its dependence on BrC and on lensing from less absorbing coatings and (2) an estimation of the most important absorbers at typical European locations.

The winter winds over Antarctica form a stable vortex. However, in 2019 the vortex was disrupted and the temperature in the polar stratosphere rose by 50°C. This event, called a sudden stratospheric warming, is a rare event in the Southern Hemisphere, with the only known major event having taken place in 2002. The 2019 event helps us unravel its causes, which are largely unknown. We have discovered a unique behaviour of the equatorial winds in 2002 and 2019 that may signal an impending SH SSW.

Boreal autumn is the main wet season over the Congo basin. Thus, changes in its onset date have a significant impact on the rainforest. This study provides compelling evidence that the cooling effect of aerosols modifies the timing and strength of the southern African easterly jet that is central to the boreal autumn wet season over the Congo rainforest. A higher boreal summer aerosol concentration is positively correlated with the boreal autumn wet season onset timing.

The performances of two MAX-DOAS inversion algorithms were evaluated for various aerosol pollution scenarios. One inversion algorithm is based on optimal estimation; the other uses a parameterized approach. In this analysis, three types of profile shapes for aerosols and NO₂ were considered: exponential, Boltzmann, and Gaussian. The evaluation results can effectively guide the application of the two inversion algorithms in the actual atmosphere and improve the accuracy of the actual inversion.

In recent years, air pollution forecasting has become an important municipal service of the government. In this study, a new spatial allocation method based on satellite remote sensing and GIS techniques was developed to address the spatial deficiency of industrial source emissions in China, providing a substantial improvement on NO₂ and PM_2.5 forecast for the Pearl River Delta/Greater Bay Area.

Which published papers have transformed our understanding of the chemical processes in the troposphere and shaped the field of atmospheric chemistry? We explore how these papers have shaped the development of the field of atmospheric chemistry and identify the major landmarks in the field of atmospheric chemistry through the lens of those papers' impact on science, legislation and environmental events.

This study presents vertical profiles of biogenic and anthropogenic secondary organic aerosols (SOAs) in the urban boundary layer based on a 325 m tower in Beijing in late summer. The increases in the isoprene and toluene SOAs with height were found to be more related to regional transport, whereas the decrease in those from monoterpenes and sesquiterpene were more subject to local emissions. Such complicated vertical distributions of SOA should be considered in future modeling work.

We present a 2-year dataset of trace gas concentrations, specifically an array of volatile organic compounds (VOCs), recorded at the Maïdo observatory, a remote tropical high-altitude site located on a small island in the southwest Indian Ocean. We found that island-scale transport is an important driver for the daily cycle of VOC concentrations. During the day, surface emissions from the island affect the atmospheric composition at Maïdo greatly, while at night this impact is strongly reduced.

Modifications in the optical properties of black carbon (BC) due to ageing are presented and quantified in this study using a state-of-the-art description scheme of BC fractal aggregates. It is shown that the relative change in BC radiative forcing can be larger than 50 % as a function of changing fractal dimension and organic content. A comprehensive parameterization scheme for coated BC optical properties is developed with applications for modelling, ambient, and laboratory-based BC studies.

The term open-air factor was coined in the 1960s, establishing that rural air had powerful germicidal properties possibly resulting from immediate products of the reaction of ozone with alkenes, unsaturated compounds ubiquitously present in natural and polluted environments. We have re-evaluated those early experiments, applying the recently substantially improved knowledge, and put them into the context of the lifetime of aerosol-borne pathogens that are so important in the Covid-19 pandemic.

This work focuses on understanding aerosol's ability to act as cloud condensation nuclei (CCN) and its variations with organic oxidation level and volatility using measurements at a rural site. Aerosol properties were examined from four air mass sources. The results help improve the accurate representation of aerosol from different ambient aerosol emissions, transformation pathways, and atmospheric processes in a climate model.

This paper investigates the impact of water uptake on aerosol optical properties, in particular the aerosol light-scattering coefficient. Although in situ measurements are performed at low relative humidity (typically at RH < 40 %), to address the climatic impact of aerosol particles it is necessary to take into account the effect that water uptake may have on the aerosol optical properties.

Measurements of aerosol and gas composition were carried out at a land–water transition site near Baltimore, MD. Gas-phase ammonia concentrations were highly elevated compared to measurements at a nearby inland site. Our analysis reveals that NH₂ was from both industrial and agricultural sources. This had a pronounced effect on aerosol chemical composition at the site, most notably contributing to episodic spikes of aerosol nitrate.

Iodine is emitted from the ocean and helps to destroy ozone in the lower atmosphere before being taken up into aerosol particles. We measured the chemical forms of iodine in aerosols over the Atlantic Ocean, because some of these forms can return to the gas phase and destroy more ozone. Our results indicate that aerosol acidity exerts a strong control on iodine speciation and therefore on its recycling behaviour and impact on ozone concentrations.

Nitrous acid (HONO) derived from wildfire emissions plays a key role in controlling atmospheric oxidation chemistry. However, the HONO budget remains poorly constrained. By combining the field-observed concentrations and novel isotopic composition (N and O) of HONO and nitrogen oxides (NO_x), we quantitatively constrained the relative contribution of each pathway to secondary HONO production and the relative importance of major atmospheric oxidants (ozone versus peroxy) in aged wildfire smoke.

The article presents a new conceptual model to describe the temporal evolution of continental fog layers, developed based on 7 years of fog measurements performed at the SIRTA observatory, France. This new paradigm relates the visibility reduction caused by fog to its vertical thickness and liquid water path and provides diagnostic variables that could substantially improve the reliability of fog dissipation nowcasting at a local scale, based on real-time profiling observation.

We provide various statistical properties for the stochastic model of eddy hopping, which is a novel cloud microphysical model that accounts for the effect of the supersaturation fluctuation at unresolved scales on the growth of cloud droplets and on spectral broadening in a turbulent cloud. Our results indicate that the model can be improved to have better fidelity to the reference data and to require less computational cost.

Methane emissions from leaks in natural gas pipes are often a large source in urban areas, but they are difficult to measure on a city-wide scale. Here we use an array of innovative methane sensors distributed around the city of Indianapolis and a new method of combining their data with an atmospheric model to accurately determine the magnitude of these emissions, which are about 70 % larger than predicted. This method can serve as a framework for cities trying to account for their emissions.

Haze caused by abundant atmospheric aerosols has become a serious environmental issue in many countries. An innovative deep-learning machine has been developed to forecast the occurrence of hazes in two Asian megacities (Beijing and Shanghai) and has achieved good overall accuracy. Using this machine, typical regional meteorological and hydrological regimes associated with haze and non-haze events in the two cities have also been, arguably for the first time, successfully categorized.

Using measurements of methane isotopes in ambient air and a 3D atmospheric transport model, in Krakow, Poland, we mainly detected fossil-fuel-related sources, coming from coal mining in Silesia and from the use of natural gas in the city. Emission inventories report large emissions from coal mine activity in Silesia, which is in agreement with our measurements. However, methane sources in the urban area of Krakow related to the use of fossil fuels might be underestimated in the inventories.

Brown carbon (BrC) fractions derived from biomass burning and coal combustion including water- and methanol-soluble organic carbon were comprehensively characterized for their optical and chemical properties, as well as oxidative potential. Moreover, the key components or functional groups that were responsible for the reactive oxygen species (ROS) generation capacity of BrC were also discussed. These findings are useful for estimation of their environmental, climate, and health impacts.

The Amazonian boundary layer is investigated during the dry season in order to better understand the processes that occur between night and day until the stage where shallow cumulus clouds become deep. Observations show that shallow to deep clouds are characterized by a shorter morning transition stage (e.g., the time needed to eliminate the stable boundary layer inversion), while higher humidity above the boundary layer favors the evolution from shallow to deep cumulus clouds.

The study of climate change relies on climate models, which require an understanding of aerosol formation. We train a machine-learning model to predict the partitioning coefficients of atmospheric molecules, which govern condensation into aerosols. The model can make instant predictions based on molecular structures with accuracy surpassing that of standard computational methods. This will allow the screening of low-volatility molecules that contribute most to aerosol formation.

The assessment of the environmental consequences of a radionuclide release depends on the estimation of its source. This paper aims to develop inverse Bayesian methods which combine transport models with measurements, in order to reconstruct the ensemble of possible sources. Three methods to quantify uncertainties based on the definition of probability distributions and the physical models are proposed and evaluated for the case of ¹⁰⁶Ru releases over Europe in 2017.

The mechanisms and kinetics of particulate sulfate formation in the atmosphere are still open questions although they have been extensively discussed. We found that uptake of SO₂ is the rate-determining step for the conversion of SO₂ to particulate sulfate. NH₄NO₃ plays an important role in AWC, the phase state of aerosol particles, and subsequently the uptake kinetics of SO₂ under high-RH conditions. This work is a good example of the feedback between aerosol physics and aerosol chemistry.

Atmospheric mercury species (GEM, GOM, PHg) are important constituents in the High Arctic due to their detrimental effects on human and ecosystem health. However, understanding their behavior in the High Arctic summer remains lacking. This research investigates the dynamics of mercury oxidation in the High Arctic summer. The cold, dry, sunlit free troposphere was associated with events of high GOM in the High Arctic summer, while individual events yielded unique origins.

We bridge the gap between satellite column observations and emissions by accounting for the dynamic lifetime of pollutants due to wind dispersion and the chemical lifetime due to chemical reactions. Applying it to the Po Valley air basin, we derive the monthly emissions of nitrogen oxides using satellite nitrogen dioxide observations. We further quantify the COVID-19-driven decline of emissions and estimate a 22 % decrease in nitrogen oxide emissions due to the pandemic in 2020.

Sulfuric acid, H₂SO₄, plays a key role in formation of secondary atmospheric aerosol particles. It is generally accepted that the major atmospheric source of H₂SO₄ is the reaction of OH radicals with SO₂. In this study, importance of an additional H₂SO₄ source via oxidation of SO₂ by stabilized Criegee intermediates was estimated based on measurements at a remote site on Cape Corsica. It was found that the oxidation of SO₂ by SCI may be an important source of H₂SO₄, especially during nighttime.

Given the hazardous nature of medicanes, studies focused on understanding and quantifying the processes governing their formation have become paramount for present and future disaster risk reduction. Therefore, enhancing the modeling and forecasting capabilities of such events is of crucial importance. In this sense, the authors find that the microphysical processes, and specifically the wind--sea salt aerosol feedback, play a key role in their development and thus should not be neglected.

We present a satellite-derived global dust climatological record over the last two decades, including the monthly mean visible dust optical depth (DAOD) and vertical distribution of dust extinction coefficient at a 2º × 5º spatial resolution derived from CALIOP and MODIS. In addition, the CALIOP climatological dataset also includes dust vertical extinction profiles. Based on these two datasets, we carried out a comprehensive comparative study of the spatial and temporal climatology of dust.

A Raman lidar was operated aboard the icebreaker Polarstern during MOSAiC and monitored aerosol and cloud layers in the central Arctic up to 30 km height. The article provides an overview of the spectrum of aerosol profiling observations and shows aerosol–cloud interaction studies for liquid-water and ice clouds. A highlight was the detection of a 10 km deep wildfire smoke layer over the North Pole up to 17 km height from the fire season of 2019, which persisted over the whole winter period.

The impact of volcanic eruptions varies with eruption season and latitude. This study simulated eruptions at different latitudes and in different seasons with a fully coupled climate model. The climate impacts of northern and southern hemispheric eruptions are reversed but are insensitive to eruption season. Results suggest that the regional climate impacts are due to the dynamical response of the climate system to radiative effects of volcanic aerosols and the subsequent regional feedbacks.

This study analyzed the nature, mechanisms and drivers for hot-and-polluted episodes (HPEs) in the Pearl River Delta, China. A total of eight HPEs were identified and can be grouped into three clusters of HPEs that were respectively driven (1) by weak subsidence and convection induced by approaching tropical cyclones, (2) by calm conditions with low wind speed in the lower atmosphere and (3) by the combination of both aforementioned conditions.

In July and August 2017, the StratoClim mission took place in Nepal with eight flights of the M-55 Geophysica at up to 20 km in the Asian monsoon anticyclone. New particle formation (NPF) next to cloud ice was detected in situ by abundant nucleation-mode aerosols (> 6 nm) along with ice particles (> 3 µm). NPF was observed mainly below the tropopause, down to 15 % being non-volatile residues. Observed intra-cloud NPF indicates its importance for the composition in the tropical tropopause layer.

Feedbacks of acidity and atmospheric multiphase chemistry in deliquesced particles and clouds are crucial for the tropospheric composition, depositions, climate, and human health. This review synthesizes the current scientific knowledge on these feedbacks using both inorganic and organic aqueous-phase chemistry. Finally, this review outlines atmospheric implications and highlights the need for future investigations with respect to reducing emissions of key acid precursors in a changing world.

Aromatic aldehydes are a family of compounds emitted into the atmosphere from both anthropogenic and biogenic sources that are formed from the degradation of aromatic hydrocarbons. Their atmospheric degradation may impact air quality. We report on their atmospheric degradation through reaction with NO₃, which is useful to estimate their atmospheric lifetimes. We have also attempted to elucidate the mechanism of these reactions via studies of isotopic substitution and quantum chemistry.

El Niño has an important influence on climate systems. There are obviously negative water vapor anomalies from radiosonde observations in the tropical western Pacific during El Niño. The tropical Hadley, Walker, and monsoon circulation variations are revealed to play different roles in the observed water vapor anomaly in different types of El Niños. The Walker (monsoon) circulation anomaly made a major contribution in the 2015/16 (2009/10) strong eastern Pacific (central Pacific) El Niño event.

The stratospheric Brewer–Dobson circulation (BDC), responsible for transporting mass, tracers and heat globally in the stratosphere, is evaluated in a set of state-of-the-art climate models. The acceleration of the BDC in response to increasing greenhouse gases is most robust in the lower stratosphere. At higher levels, the well-known inconsistency between model and observational BDC trends can be partly reconciled by accounting for limited sampling and large uncertainties in the observations.

Kelvin–Helmholtz (K–H) clouds embedded in a stratiform precipitation event were uncovered via radar Doppler spectral analysis. Given the unprecedented detail of the observations, we show that multiple populations of secondary ice columns were generated in the pockets where larger cloud droplets are formed and not at some constant level within the cloud. Our results highlight that the K–H instability is favorable for liquid droplet growth and secondary ice formation.

Ozone production at an urban site in Delhi is sensitive to volatile organic compound (VOC) concentrations, particularly those of the aromatic, monoterpene, and alkene VOC classes. The change in ozone production by varying atmospheric pollutants according to their sources, as defined in an emissions inventory, is investigated. The study suggests that reducing road transport emissions alone does not reduce reactive VOCs in the atmosphere enough to perturb an increase in ozone production.

We study large- and small-scale gravity wave cases observed in both airglow imagery and meteor radar data obtained during the SIMONe campaign carried out in early November 2018. We calculate the intrinsic features of several waves and estimate their impact in the mesosphere and lower thermosphere region via transferring energy and momentum to the atmosphere. We also associate cases of large-scale waves with secondary wave generation in the stratosphere.

There is a lack of detailed understanding of NMVOC emissions from the use of volatile chemical products (VCPs) in China. This study used a mass balance method to compile a long-term emission inventory for solvent use (including coatings, adhesives, inks, pesticides, cleaners and personal care products) in China during 2000–2017. The striking growth and recent trend of solvent use NMVOC emissions can give important implications for air quality modeling and NMVOC control strategies in China.

Within this work we determined the rate coefficients and products of the reaction of unsaturated ketones with OH radicals in an effort to complete the gaps in the knowledge needed for modelling chemistry in the atmosphere. Both substances are potentially emitted by biomass burning, industrial activities or formed in the troposphere by oxidation of terpenes. As products we identified aldehydes and ketones which in turn are known to be responsible for the transportation of NO_x species.

Heat-related illnesses are of increasing concern in China given its rapid urbanisation and our ever-warming climate. We examine the relative impacts that land surface properties and anthropogenic heat have on the urban heat island (UHI) in Beijing using ADMS-Urban. Air temperature measurements and satellite-derived land surface temperatures provide valuable means of evaluating modelled spatiotemporal variations. This work provides critical information for urban planners and UHI mitigation.

Secondary sulfate aerosols are an important component of fine particles in severe air pollution events. We calculated the sulfate formation rates via a state-of-the-art multiphase model constrained to the observed values. We showed that transition metals in urban aerosols contribute significantly to sulfate formation during haze periods and thus play an important role in mitigation strategies and public health measures in megacities worldwide.