Human activities have greatly impacted the Earth system so much so that it has ushered in a new epoch - the Anthropocene. The consequent changes - observed and predicted – occur in the oceans, the terrestrial regions, and the biosphere, and have raised important societal issues such as climate change, ocean acidification, air quality degradation, and ozone layer depletion.

The central component that leads to changes and impacts are the processes that alter the composition of the atmosphere. It is time to take a closer look at the processes that change the composition the Earth’s atmosphere to ensure that they are understood and represented accurately in models, whose predictions underpin societal actions.

This Discussion will focus on emerging issues such as interactions between anthropogenic and biogenic emissions, new mechanisms important for atmospheric chemistry, the impacts of climate on air quality, and new instrumental tools and platforms for atmospheric chemistry.