We investigate the distribution and trends of surface ozone and its precursors over Ireland using advanced modelling to determine the drivers of ozone. Trajectory analysis is used to trace the origins of air masses, revealing the impact of transboundary pollution and atmospheric transport. The rising trend has been observed at urban sites over the past two decades, but without a similar trend at coastal sites. Coastal areas consistently show higher ozone levels than rural and urban areas.

Halogenated alkanes, alkenes, and oxygenated compounds play an important role in atmospheric chemistry. This article, the ninth in the series, presents kinetic and photochemical data sheets evaluated by the International Union of Pure and Applied Chemistry (IUPAC) Task Group on Atmospheric Chemical Kinetic Data Evaluation. It covers the gas-phase reactions (with HO radicals, NO₃ radicals, and ozone) and photolysis of halogenated organic compounds. These data are important for atmospheric models.

We present analysis of long-term aerosol measurements from two sites in Colorado. In this work, we characterize seasonal trends of aerosol optical properties for both sites and perform trend analysis to investigate changes in sources over time. We show that there is a significant increase in the influence of extreme events like smoke and dust, and explore the relationship between optical properties to identify aerosol types and temporal patterns at the two sites.

Ice in the Arctic clouds is initiated by rare particles, and their properties are not well understood due to atmospheric processing. By combining microscopy with freezing experiments, we found that both chemical composition and the thickness and morphological configuration of organic coatings influence ice formation. This finding highlights the importance of particle surface chemistry in cloud formation and offers new insights into how Arctic aerosols influence cloud formation.

We evaluate five chemical reanalysis products to assess their potential to provide useful information on tropospheric ozone variability. We find that the reanalyses produce consistent information on ozone variations in the free troposphere, but have large discrepancies at the surface. The results suggests that improvements in the reanalyses are needed to better exploit the assimilated observations to enhance the utility of the reanalysis products at the surface.