During the DACCIWA campaign in West Africa, we found a 35 % increase in the cloud droplet concentration that formed in a polluted compared with a less polluted environment and a decrease of 17 % in effective droplet diameter. Radiative transfer simulations, based on the measured cloud properties, reveal that these low-level polluted clouds radiate only 2.6 % more energy back to space, compared with a less polluted cloud. The corresponding additional decrease in temperature is rather small.

We developed a dataset of the long-term (2005–2020) variabilities of China’s nitrogen and sulfur deposition, with multiple statistical models that combine available observations and chemistry transport modeling. We demonstrated the strong impact of human activities and national pollution control actions on the spatiotemporal changes in deposition and indicated a relatively small benefit of emission abatement on deposition (and thereby ecological risk) for China compared to Europe and the USA.

Warm conveyor belts (WCBs) are cloud- and precipitation-producing airstreams in extratropical cyclones that are important for the large-scale flow and cloud radiative forcing. We analyze cloud formation processes during WCB ascent in a two-moment microphysics scheme. Quantification of individual diabatic heating rates shows the importance of condensation, vapor deposition, rain evaporation, melting, and cloud-top radiative cooling for total heating and WCB-related potential vorticity structure.

A new steady-state gas–particle partitioning model of polycyclic aromatic hydrocarbons was established based on the level-III multimedia fugacity model, which proved that the particulate proportion of PAHs in emissions was a crucial factor for G–P partitioning of PAHs. In addition, gaseous and particulate interference was also derived in the new steady-state model determined by the particulate proportion in emission that could derivate the G–P partitioning quotients from the equilibrium state.

Marine boundary layer clouds remain poorly predicted in global climate models due to multiple entangled uncertainty sources. This study uses the in situ observations from a recent field campaign to constrain and evaluate cloud physics in a simplified version of a climate model. Progress and remaining issues in the cloud physics parameterizations are identified. We systematically evaluate the impacts of large-scale forcing, microphysical scheme, and aerosol concentrations on the cloud property.

We quantify the emissions from the marine sector in northern France, whether from natural or human-made sources. Therefore, a 1-year PM₁₀ sampling campaign was conducted at a French coastal site. Results showed that sea salts contributed 37 %, while secondary nitrate and sulfate contributed 42 %, biomass burning 8 %, and heavy-fuel-oil combustion from shipping emissions 5 %. Sources contributing more than 80 % of PM₁₀ are of regional and/or long-range origin.

Dust aerosols affect our climate differently depending on their mineral composition. We include dust mineralogy in an atmospheric model considering two existing soil maps, which still have large associated uncertainties. The soil data and the distribution of the minerals in different aerosol sizes are key to our model performance. We find significant regional variations in climate-relevant variables, which supports including mineralogy in our current models and the need for improved soil maps.

Ambient particle populations and associated ice-nucleating particles (INPs) were examined from particle samples collected on board aircraft in the marine boundary layer and free troposphere in the eastern North Atlantic during summer and winter. Chemical imaging shows distinct differences in the particle populations seasonally and with sampling altitudes, which are reflected in the INP types. Freezing parameterizations are derived for implementation in cloud-resolving and climate models.

Due to a lack of observations, the structure of the Arctic atmospheric boundary layer (ABL) remains to be further explored. By analyzing a year-round radiosonde dataset collected over the Arctic sea-ice surface, we found the annual cycle of the ABL height (ABLH) is primarily controlled by the evolution of ABL thermal structure, and the surface conditions also show a high correlation with ABLH variation. In addition, the Arctic ABLH is found to be decreased in summer compared with 20 years ago.

We present a new method to analyse the influence of atmospheric rivers (ARs), cyclones, and fronts on the precipitation in the Arctic, based on two campaigns: ACLOUD (early summer 2017) and AFLUX (early spring 2019). There are differences between both campaign periods: in early summer, the precipitation is mostly related to ARs and fronts, especially when they are co-located, while in early spring, cyclones isolated from ARs and fronts contributed most to the precipitation.

The COVID-19 pandemic, which was caused by the SARS-CoV-2 virus, emerged in 2019, and its still evolving variants have resulted in unprecedented shifts in human activities and anthropogenic emissions into the Earth's atmosphere. We present monthly nitrogen oxide emissions over three major continents from May 2018 to January 2023 to capture variations before and after the COVID-19 pandemic. We focus on a diverse collection of 54 cities to quantify the post-COVID-19 perturbations.

Aerosol forcing of Earth’s energy balance has persisted as a major cause of uncertainty in climate simulations over generations of climate model development. We show that structural deficiencies in a climate model are exposed by comprehensively exploring parametric uncertainty and that these deficiencies limit how much the model uncertainty can be reduced through observational constraint. This provides a future pathway towards building models with greater physical realism and lower uncertainty.

We investigated the contribution of inland shipping to air pollution at the river Rhine in Germany. Land-based measurements of gaseous and particulate pollutants were carried out for more than 1 year to provide a realistic estimate for the exposure of people to air pollution close to the riverside. Emissions of nitrogen oxides and particulate matter relative to the amount of fuel used, as well as their dependence on ship size, engine type and operating conditions, were examined.

We set up a new parameterization for 1.4 nm particle formation rates from sulfuric acid–dimethylamine (SA–DMA) nucleation, fully including the effects of coagulation scavenging and cluster stability. Incorporating the new parameterization into 3-D chemical transport models, we achieved better consistencies between simulation results and observation data. This new parameterization provides new insights into atmospheric nucleation simulations and its effects on atmospheric pollution or health.

Although photooxidants are important in airborne particles, little is known of their concentrations. By measuring oxidants in a series of particle dilutions, we predict their concentrations in aerosol liquid water (ALW). We find ^•OH concentrations in ALW are on the order of 10⁻¹⁵ M, similar to their cloud/fog values, while oxidizing triplet excited states and singlet molecular oxygen have ALW values of ca. 10⁻¹³ M and 10⁻¹² M, respectively, roughly 10–100 times higher than in cloud/fog drops.

This study quantifies urban CO₂ emissions via an atmospheric inversion for the Paris metropolitan area over a 6-year period from 2016 to 2021. Results show a long-term decreasing trend of about 2 % ± 0.6 % per year in the annual CO₂ emissions over Paris. We conclude that our current capacity can deliver near-real-time CO₂ emission estimates at the city scale in under a month, and the results agree within 10 % with independent estimates from multiple city-scale inventories.

Pyrolysis is the thermal decomposition of fuels like wood which occurs during combustion or as an isolated process. During combustion, some pyrolysis products are emitted directly, while others are oxidized in the combustion process. This work describes the chemical composition of particle-phase pyrolysis products in order to investigate both the uncombusted emissions from wildfires and the fuel that participates in combustion.

We studied the variability and molecular composition of ambient oxidized organic nitrogen (OON) in both gas and particle phases using a state-of-the-art online mass spectrometer in urban air. Biomass burning and secondary formation were found to be the two major sources of OON. Daytime nitrate radical chemistry for OON formation was more important than previously thought. Our results improved the understanding of the sources and molecular composition of OON in the polluted urban atmosphere.

The primary uncertainty in how strongly Earth's climate has been perturbed by human activities comes from the unknown radiative impact of aerosol changes. Accurately quantifying these forcings – and their sub-components – in climate models is crucial for understanding the past and future simulated climate. In this study we describe biases in previously published estimates of aerosol radiative forcing in climate models and provide corrected estimates along with code for users to compute them.

We present a fast method to evaluate carbon monoxide emissions from cities in Africa. Carbon monoxide is important for climate change in an indirect way, as it is linked to ozone, methane, and carbon dioxide. Our measurements are made with a satellite that sees the entire globe every single day. This means that we can check from space whether the current knowledge of emission rates is up to date. We make the comparison and show that the emission rates in northern Africa are underestimated.

Open burning of household and municipal solid waste is a common practice in developing countries and is a significant source of air pollution. However, few studies have measured emissions from open burning of waste. This study determined gas and particulate emissions from open burning of 10 types of household solid-waste materials. These results can improve emission inventories, air quality management, and assessment of the health and climate effects of open burning of household waste.

Wildfire smoke is a significant source of airborne atmospheric particles that can absorb sunlight. Extreme fires in particular, such as those during the 2019–2020 Australian wildfire season (Black Summer fires), can considerably affect our climate system. In the present study, we investigate the various effects of Australian smoke using a global climate model to clarify how the Earth's atmosphere, including its circulation systems, adjusted to the extraordinary amount of Australian smoke.

The influence of human-produced aerosols on clouds remains one of the uncertainties in radiative forcing of Earth’s climate. Measurements of aerosol chemistry from sources around the Philippines illustrate the linkage between aerosol chemical composition and cloud droplet characteristics. Differences in aerosol chemical composition in the marine layer from biomass burning, industrial, ship-produced, and marine aerosols are shown to impact cloud microphysical structure just above cloud base.

In hydration, an apparent water diffusion hindrance by an organic surfactant shell was confirmed, raising the inorganic deliquescence relative humidity (RH) to a nearly saturated condition. In dehydration, phase separations were observed for inorganic surfactant systems, showing a strong dependence on the organic molecular oxygen-to-carbon ratio. Our results could improve fundamental knowledge about aerosol mixing states and decrease uncertainty in model estimations of global radiative effects.

Biogenic secondary organic aerosols (SOAs) account for a large fraction of fine aerosol at the global scale. Using long-term measurements and a climate model, we investigate anthropogenic impacts on biogenic SOA at both decadal and centennial timescales. Results show that despite reductions in biogenic precursor emissions, SOA has been strongly amplified by anthropogenic emissions since the preindustrial era and exerts a cooling radiative forcing.