The rate of collisions between molecules or clusters is used to determine particle formation in the atmosphere. The basic approach is to treat the colliding particles as noninteracting hard spheres. By using atomistic simulations with a realistic force field and theoretical approaches, we showed that the actual collision rate of two sulfuric acid molecules is more than twice as high as that for hard spheres. The results of this study will improve models of atmospheric particle growth.

In this paper we explore the connection between changes in surface temperature and changes in ozone pollution. While explanations for this connection have been proposed in the past, we attempt to better quantify them using models and statistics. We find that some of the most commonly cited mechanisms, including biogenic emissions and temperature-dependent chemical processes, can explain less than half of the O₃–T correlation. Meteorology is identified as the most likely driver for the remainder.

We present the new Binary Activity Thermodynamics (BAT) model, which is a water-sensitive reduced-complexity organic aerosol thermodynamics model. It can use bulk properties like O : C, molar mass, and RH to predict organic activity coefficients and water uptake behavior. We show applications in RH-dependent organic co-condensation, liquid–liquid phase separation, and Kohler curve predictions, and we validate the BAT model against laboratory measurements.

A novel methodology to monitor atmospheric aerosol components using remote sensing is presented. The concept is realized within the GRASP (Generalized Retrieval of Aerosol and Surface Properties) project. Application to POLDER/PARASOL and AERONET observations yielded the spatial and temporal variability of absorbing and non-absorbing insoluble and soluble aerosol species in the fine and coarse size fractions. This presents the global-scale aerosol component derived from satellite measurements.

Aerosol vertical information is critical to quantify the influences of aerosol on the climate and environment; however, large uncertainties still persist in model simulations. Global aerosol vertical distributions are more accurately simulated by assimilating the vertical aerosol extinction coefficients from the Cloud–Aerosol Lidar with Orthogonal Polarization (CALIOP).

Calculations have been made with the regional-scale EMEP chemical transport model covering Europe and the sea areas surrounding Europe, including much of the North Atlantic. The main focus is on the effects on air pollution as well as depositions of sulfur and nitrogen following the implementation of stricter sulfur emission regulations from 1 January 2015 for ships operating in the Baltic Sea. We also include a study on the effects of future (2030) emissions changes.

This study investigates differences in atmospheric conditions between nights with and without low-level stratus clouds (LLCs) over southern West Africa. We use high-quality observations collected during 2016 summer monsoon season and the ERA5 reanalysis data set. Our results show that the formation of LLCs depends on the interplay between the onset time and strength of the nocturnal low-level jet, horizontal cold-air advection, and the overall moisture level in the whole region.

Shallow convective clouds are among the most common and least understood clouds in the atmosphere. Here we present simulations of realistic, shallow cloud fields in a large domain, in contrast to typical idealised simulations, and find that in these simulations the response to aerosol perturbations is different.

We employed Kolmogorov–Zurbenko filtering and WRF-CMAQ to quantify the relative contribution of meteorological variations and emission reduction to PM_2.5 reduction in Beijing from 2013 to 2017, which is crucial to evaluate the Five-year Clean Air Action Plan. Both models suggested that despite favourable meteorological conditions, the control of anthropogenic emissions accounted for around 80 % of PM_2.5 reduction in Beijing. Therefore, such a long-term clean air plan should be continued.

With satellite measurements and transport models, we show that a plume resulting from strong Canadian fires in July/August 2017 was not only distributed throughout the northern/higher latitudes, but also reached the faraway tropics, aided by the circulation of Asian monsoon anticyclone. The regional climate impact in the wider Asian monsoon area in September exceeds the impact of the Asian tropopause aerosol layer by a factor of ~ 3 and compares to that of an advected moderate volcanic eruption.

Biogenic non-methane volatile organic compounds (NMVOCs) emitted from vegetation play a significant role in air quality and climate. However, there are large uncertainties in their role for climate. We present a Bayesian approach to estimate carbon monoxide fluxes that are chemically produced from biogenic sources. This provides independent constraints on models that predict biogenic emissions in order improve their capability for predicting air quality and future climate scenarios.

Atmospheric mineral dust has been identified as an important contributor to cloud formation and cloud properties that influence the Earth's climate, yet experimental measurements of climate model parameters currently disagree. This study demonstrates current best practices for analyzing water adsorption measurements, resulting in significantly improved agreement among experimental practices. As such, more accurate parameters can be used to improve simulations of aerosol climate effects.

Atmospheric furan is a primary and secondary pollutant in the atmosphere, and its emission contributes to the formation of ultrafine particles and ground-level ozone. The present study demonstrates the effect of NO_x and humidity on secondary organic aerosol (SOA) formation during the furan–NO_x–NaCl photooxidation. Furthermore, the results illustrate the importance of studying SOA formation over a comprehensive range of environmental conditions.

Owing to the gradual implementation of emission control zone (ECA) regulations, feasible technology for the surveillance of compliance with respect to fuel sulfur content is in high demand. We presented shore-based MAX-DOAS measurements of ship-emitted SO₂ and NO₂ under different traffic conditions. The results of this study indicate that this technique has high potential as a fast and accurate way to surveil ship emissions and fuel sulfur content.

The study aims at addressing the challenge in efficient quantification of the nonlinear response of air pollution to precursor emission perturbations. The newly developed observable response indicators can be easily calculated by a combination of ambient concentrations of certain species. Their capability in representing the spatial and temporal variation in PM_2.5 and O₃ chemistry has also been well evaluated and applied in China.

BRAM2 is a 13-year reanalysis of the chemical composition from the upper troposphere to the lower mesosphere based on the assimilation of the Microwave Limb Sounder observations where eight species are assimilated: O₃, H₂O, N₂O, HNO₃, HCl, ClO, CH₃Cl and CO. BRAM2 agrees generally well with independent observations in the middle stratosphere, the polar vortex and the upper troposphere–lower stratosphere but also shows several issues in the model and in the observations.

We analyse nitrification of the LMS in the Arctic winter 2015–2016 based on GLORIA measurements. Vertical cross sections of HNO₃ for several flights show complex fine–scale structures and enhanced values down to 9 km. The extent of overall nitrification is quantified based on HNO₃–O₃ correlations and reaches between 5 ppbv and 7 ppbv at potential temperature levels between 350 and 380 K. Further, we compare our result with the atmospheric model CLaMS.

The role of hydroxyl radical changes in methane trends is debated, hindering our understanding of the methane cycle. This study quantifies how uncertainties in the hydroxyl radical may influence methane abundance in the atmosphere based on the inter-model comparison of hydroxyl radical fields and model simulations of CH₄ abundance with different hydroxyl radical scenarios during 2000–2016. We show that hydroxyl radical changes could contribute up to 54 % of model-simulated methane biases.