Tropospheric ozone is an extremely important atmospheric compound as it oxidises, and thus removes, chemical compounds in the atmosphere. One important source in the troposphere are anthropogenic emissions. At elevated concentrations ozone presents a pollutant that is harmful to human health and ecosystems, and it acts as a short-lived greenhouse gas in the upper troposphere. Based on previously developed community models to describe the spatial and temporal variation of tropospheric ozone, this highly controversially discussed Opinion article proposes the establishment of a conceptual, simplified, but widely accepted tropospheric ozone model to facilitate communication between different communities concerned with different ozone impacts, and between ozone research and policy. This step could pave the way for a coordinated global action to improve air quality standards worldwide in an efficient and cost-effective manner.

Giant CCN have long been recognised as highly important in warm marine clouds, as while these are low in number, they often dictate precipitation rates and thus many climate-important properties such as cloud optical thickness and lifetime. However, measuring these particles is remains challenging on a technical level and many models of their production are poorly constrained. This paper presents the results using a new methodology and goes on to explore the role of coastlines in enhancing wave breaking and thus giant CCN production.

This provocative opinion piece examines the theoretical, numerical, and observational evidence in support of two highly cited proposed mechanisms for invigorating deep convective clouds through higher aerosol concentrations. Both start with high concentrations of water droplets. Through cold-phase invigoration, precipitation is reduced allowing for greater release of latent heat from freezing higher up in clouds. With warm-phase invigoration, increased latent heating occurs lower down due to accelerated liquid condensation. In both cases, the article persuasively argues from a variety of standpoints that the evidence to support the importance of the effects is weak, particularly once the full complexity of clouds and their interactions with their environment is fully taken into account. Concrete suggestions are made for improving definition, observations, and modeling of the problem, but also an admonishment that attention in the field might be better directed towards more fruitful aspects of the aerosol-cloud interaction problem.