This study presents and compares inorganic chlorine (Cl_y) derived from observations with the HALO research aircraft in the Antarctic late winter–early fall 2019 and the Arctic winter 2015–2016. Trend-corrected correlations from the Northern Hemisphere show excellent agreement with those from the Southern Hemisphere. After observation allocation inside and outside the vortex based on N₂O measurements, results of the two campaigns reveal substantial differences in Cl_y within the respective vortex.

In this study we quantify how a new way of modeling the formation of new particles in the atmosphere affects the estimated cooling from aerosol–cloud interactions since pre-industrial times. Our improved scheme merges two common approaches to aerosol modeling: a sectional scheme for treating early growth and the pre-existing modal scheme in NorESM. We find that the cooling from aerosol–cloud interactions since pre-industrial times is reduced by 10 % when the new scheme is used.

A global climate model is applied to simulate the impact of aviation soot on natural cirrus clouds. A large number of numerical experiments are performed to analyse how the quantification of the resulting climate impact is affected by known uncertainties. These concern the ability of aviation soot to nucleate ice and the role of model dynamics. Our results show that both aspects are important for the quantification of this effect and that discrepancies among different model studies still exist.

The article introduces the ACP readership to ongoing research in Germany on cloud- and precipitation-related process information inherent in polarimetric radar measurements, outlines pathways to inform atmospheric models with radar-based information, and points to remaining challenges towards an improved fusion of radar polarimetry and atmospheric modelling.

We find that ice-nucleating particles (INPs), aerosols that can initiate the freezing of cloud droplets, cause substantial changes to the properties of radiatively important convectively generated anvil cirrus. The number concentration of INPs had a large effect on ice crystal number concentration while the INP temperature dependence controlled ice crystal size and cloud fraction. The results indicate information on INP number and source is necessary for the representation of cloud glaciation.

Quantification of anthropogenic CH₄ emissions remains challenging, but it is essential for near-term climate mitigation strategies. We use airborne remote sensing observations to assess bottom-up estimates of coal mining emissions from one of Europe's largest CH₄ emission hot spots located in Poland. The analysis reveals that emissions from small groups of shafts can be disentangled, but caution is advised when comparing observations to commonly reported annual emissions.

We present the first ship-based in situ measurements of formaldehyde (HCHO), hydroxyl radicals (OH) and the OH reactivity around the Arabian Peninsula. Regression analysis of the HCHO production rate and the related OH chemistry revealed the regional HCHO yield α_eff, which represents the different chemical regimes encountered. Highest values were found for the Arabian Gulf (also known as the Persian Gulf), which highlights this region as a hotspot of photochemical air pollution.

Larval feeding and fungal infections of leaves can greatly change the emission of volatile compounds from plants and thereby influence aerosol processes in the air. We developed a model that considers the dynamics of larvae and fungi and the dependency of the emission on the severity of stress. We show that the infections can be highly atmospherically relevant during long periods of time and at times more important to consider than the parameters that are currently used in emission models.

This paper explores the impacts of dust on summertime convective cloud and precipitation through a numerical experiment. The result indicates that the long-range-transported dust can notably affect the properties of convective cloud and precipitation by enhancing immersion freezing and invigorating convection. We also analyze the different dust effects predicted by the Morrison and SBM schemes, which are partially attributed to the saturation adjustment approach utilized in the bulk schemes.

Semi-arid ecosystems such as those in Australia are evolving and might play an essential role in the future of climate change. We use carbon dioxide concentrations derived from the OCO-2 satellite instrument and a regional transport model to understand if Australia was a carbon sink or source of CO₂ in 2015. Our research's main findings suggest that Australia acted as a carbon sink of about −0.41 ± 0.08 petagrams of carbon in 2015, driven primarily by savanna and sparsely vegetated ecosystems.

Our study explores the variation in the occurrence date, peak amplitude and wave period for eastward waves and the role of instability, background wind structure and the critical layer in eastward wave propagation and amplification.

Interactions of aerosol particles with clouds represent a large uncertainty in estimates of climate change. Properties of aerosol particles control their ability to act as cloud condensation nuclei. Using aerosol measurements in the Amazon, we performed model studies to compare predicted and measured cloud droplet number concentrations at cloud bases. Our results confirm previous estimates of particle hygroscopicity in this region.

Lightning-ignited fires tend to occur in remote areas and can spread significantly before suppression. Long continuing current (LCC) lightning, preferably taking place in dry thunderstorms, is believed to be the main precursor of lightning-ignited fires. We analyze fire databases of lightning-ignited fires in the Mediterranean basin and report the shared meteorological conditions of fire- and LCC-lightning-producing thunderstorms. These results can be useful to improve fire forecasting methods.

Metallurgical industry in Kola peninsula is a large source of air pollution in the (sub-)Arctic domain. Sulfur dioxide emissions from the ore smelters are transported across large areas. We investigated sulfur dioxide and its transformation to sulfuric acid aerosol particles during winter months in Finnish Lapland, close to Kola industrial areas. We observed intense formation of new aerosol particles despite the low solar radiation intensity, often required for new particle formation elsewhere.

In order to have confidence in atmospheric predictions, it is important to know how well different numerical model simulations of the Earth’s atmosphere agree with one another. This work compares four different data assimilation models that extend to or beyond the mesosphere. Results shown here demonstrate that while the models are in close agreement below ~50 km, large differences arise at higher altitudes in the mesosphere and lower thermosphere that will need to be reconciled in the future.

We demonstrate a novel application using air quality station data to derive 3-decade-averaged emissions from the Coal Oil Point (COP) seep field, a highly spatially and temporally variable geological migration system. Emissions were 19 Gg per year, suggesting that the COP seep field contributes 0.27 % of the global marine seep budget based on a recent estimate. This provides an advance over snapshot survey values by accounting for seasonal and interannual variations.

In this study, the authors used a single-particle soot photometer (SP2) to characterize the particle size, mixing state, and optical properties of black carbon aerosols in rural areas of the North China Plain in winter. Relatively warm and high-RH environments (RH > 50 %, −4° < T < 4 °) were more favorable to rBC aging than dry and cold environments (RH < 60 %, T < −8°). The paper emphasizes the importance of meteorological parameters in the mixing state of black carbon.

Our lidar observations reveal the complete microphysical process of hydrometeors falling from mid-level stratiform clouds. We find that the surface rainfall begins as supercooled mixed-phase hydrometeors fall out of a liquid parent cloud base. We find also that the collision–coalescence growth of precipitating raindrops and subsequent spontaneous breakup always occur around 0.6 km altitude during surface rainfalls. Our findings provide new insights into stratiform precipitation formation.

We show that the Atlantic Ocean is the major driver of interannual variability in dust over South Asia since the second decade of the 21st century. This is a shift from the previously important role played by the Pacific Ocean in controlling dust over this region. Following the end of the recent global warming hiatus, anomalies of the North Atlantic sea surface temperature have remotely invoked a weakening of the South Asian monsoon and a strengthening of the dust-bearing northwesterlies.

Aerosol–cloud interactions constitute the most uncertain contribution to climate change. The uptake kinetics of water by aerosol is a central process of cloud droplet formation, yet its molecular-scale mechanism is unknown. We use molecular simulations to study this process for phase-separated organic particles. Our results explain the increased cloud condensation activity of such particles and can be generalized over various compositions, thus possibly serving as a basis for future models.

We quantified different types of marine aerosols and explored the Cl depletion of sea salt aerosol (SSA) in the eastern China seas and the northwestern Pacific Ocean. We found that anthropogenic acidic gases in the troposphere were transported longer distances compared to the anthropogenic aerosols and could significantly impact remote marine aerosols. Meanwhile, variations of chloride depletion in SSA can serve as a potential indicator for anthropogenic gaseous pollutants in remote marine air.

Aerosol mixing state is an important emergent property that affects aerosol radiative forcing and aerosol–cloud interactions, but it has not been easy to constrain this property globally. We present a framework for evaluating the error in aerosol mixing state induced by aerosol representation assumptions, which is one of the important contributors to structural uncertainty in aerosol models. Our study provides insights into potential improvements to model process representation for aerosols.

With the rising food need, more intense agricultural activities will cause substantial perturbations to the nitrogen cycle, aggravating surface air pollution and imposing stress on terrestrial ecosystems. We studied how these ecosystem changes may modify biosphere–atmosphere exchanges, and further exert secondary effects on air quality, and demonstrated a link between agricultural activities and ozone air quality via the modulation of vegetation and soil biogeochemistry by nitrogen deposition.

A series of chamber experiments was performed to probe the individual and common effects of NH₃ and NO_x on toluene secondary organic aerosol (SOA) formation through OH photooxidation. The synergetic effects of NH₃ and NO_x on the toluene SOA concentration and optical absorption were observed. The higher-volatility products formed in the presence of NO_x could precipitate into the particle phase when NH₃ was added. The formation pathways of N-containing OAs through NO_x or NH₃ are also discussed.

For the first time, we accurately modelled the optical properties of the biomass burning aerosols (BBA) observed over the Southeast Atlantic region during their transport above clouds and over their source regions, combining a meteorology coupled with chemistry model (WRF-Chem) with innovative satellite absorbing aerosol retrievals (POLDER-3). Our results suggest a low but non-negligible brown carbon fraction (3 %) for the chemical composition of the BBA plumes observed over the source regions.

This paper investigates the mechanisms involved in the dispersion, structure, and mixing in the vertical column of atmospheric pollen, using observations of pollen concentration obtained at the ground and its stratification in the atmosphere measured by a lidar (laser radar), as well as an atmospheric transport model and a simplified pollen module developed especially for this study. The largest pollen concentration difference between the ground and the layers above is observed during nighttime.

This study examine two benefits of urban forest, thermal mitigation and carbon uptake. Our analysis indicates that the urban forest reduces both the warming trend and urban heat island intensity. Urban forest is a net CO₂ source despite larger photosynthetic carbon uptake because of strong contribution of ecosystem respiration, which can be attributed to the substantial amount of soil organic carbon by intensive historical soil use and warm temperature in a city.

Due to the widespread use of plastics high amounts of waste are burned in households worldwide, emitting vast amounts of PM₁₀ and PAHs into the atmosphere. In this work different types of common plastics were burned in the laboratory with a view to identifying potentially specific tracer compounds and determining their emission factors. The compounds found were also successfully identified in atmospheric PM₁₀ samples, indicating their potential use as ambient tracers for illegal waste burning.

We analyze observations from year-long measurements at Athens, Greece. Nighttime wintertime PAH levels are 4 times higher than daytime, and wintertime values are 15 times higher than summertime. Biomass burning aerosol during wintertime pollution events is responsible for these significant wintertime enhancements and accounts for 43 % of the population exposure to PAH carcinogenic risk. Biomass burning poses additional health risks beyond those associated with the high PM levels that develop.

We characterized the connection between new particle formation (NPF) events in terms of frequency, intensity and growth at a near-highway location in central Beijing and at a background mountain site 80 km away. Due to the substantial contribution of NPF to the global aerosol budget, identifying the conditions that promote the occurrence of regional NPF events could help understand their contribution on a large scale and would improve their implementation in global models.

The radon tracer method is applied to atmospheric methane and radon observations from the upper Rhine valley to independently estimate methane emissions from the region. Comparison of our top-down results with bottom-up inventory data requires high-resolution footprint modelling and representative radon flux data. In agreement with inventories, observed emissions decreased, but only until 2005. A limitation of this method is that point-source emissions are not captured or not fully captured.

In this study we analyse the output of a chemistry and transport model together with observations of different meteorological and compositional variables to demonstrate the link between sudden stratospheric warming and transport of stratospheric air to the surface in the subpolar regions of Europe during the cold season. Our findings have particular implications for atmospheric composition since climate projections indicate more frequent sudden stratospheric warming under a warmer climate.

Particulate amines play important roles in new particle formation, aerosol acidity, and hygroscopicity. Most of the field observations did not distinguish the different behavior of each type amine under the same ambient influencing factors. In this study, two amine-containing single particles exhibited different mixing states and disparate enrichment of secondary organics, which provide insight into the discriminated fates of organics during the formation and evolution processes.

This study brings together long-term ground-based remote-sensing observations of mixed-phase clouds at three key locations of aerosol–cloud interactions in the Northern and Southern Hemisphere midlatitudes. The findings contribute several new aspects on the nature of the excess of supercooled liquid clouds in the Southern Hemisphere, such as a long-term lidar-based estimate of ice-nucleating particle profiles as well as the effects of boundary layer coupling and gravity waves on ice formation.

Photochemical pollution over the North China Plain (NCP) is attracting much concern. Our observations at a rural site in the NCP identified high peroxyacetyl nitrate (PAN) concentrations, even on cold days. Increased acetaldehyde concentration and hydroxyl radical production rates drive fast PAN formation. Moreover, our study emphasizes the importance of formaldehyde photolysis in PAN formation and calls for implementing strict volatile organic compound controls after summer over the NCP.

African dust aerosols can travel thousands of kilometers and reach the Caribbean and other places, where they can serve as ice and cloud condensation nuclei and alter precipitation patterns. Cloud microphysical properties (droplet number and size) were measured in a Caribbean tropical montane cloud forest along with models and satellite products. The results of the study suggest that meteorology and air mass history are more important for cloud processes than aerosols transported from Africa.

Special microscopic particles called ice-nucleating particles (INPs) are essential for ice crystals to form in the atmosphere. INPs are sparse and their atmospheric concentration and properties are not well understood. Mineral dust particles make up a significant fraction of INPs but how much remains unknown. Here, we address this knowledge gap by studying periods when mineral particles are present in large quantities at a mountaintop station in central Europe.

In this study, the black carbon (BC) mixing state index (χ) is developed to quantify the dispersion of ambient black carbon aerosol mixing states based on binary systems of BC and other non-black carbon components. We demonstrate that the BC light absorption enhancement increases with χ for the same MR, which indicates that χ can be employed as a factor to constrain the light absorption enhancement of ambient BC.

Several studies evaluate aerosol–cloud interactions, but only a few attempted to describe how clouds modify aerosol properties. This study evaluates the effect of weather events on the particle size distribution at the ATTO, combining remote sensing and in situ data. Ultrafine, Aitken and accumulation particles modes have different behaviors for the diurnal cycle and for rainfall events. This study opens up new scientific questions that need to be pursued in detail in new field campaigns.

We performed a long-term investigation of ambient volatile organic compounds (VOCs) in an industrial area in Nanjing, China. Followed by alkanes, halocarbons and aromatics were the most abundant VOC groups. Vehicle-related emissions were the major VOC sources in the study area. Aromatic and alkene VOCs were responsible for most of the atmospheric reactions.

We use 2010–2015 surface and satellite observations to disentangle methane from anthropogenic and natural sources in Canada. Using a chemical transport model (GEOS-Chem), the mismatch between modelled and observed methane concentrations can be used to infer emissions according to Bayesian statistics. Compared to prior knowledge, we show higher anthropogenic emissions attributed to energy and/or agriculture in Western Canada and lower natural emissions from Boreal wetlands.