Paul J. Crutzen - a pioneer in Earth system science and a founding member of the journal Atmospheric Chemistry and Physics

Paul Jozef Crutzen was a pioneer in the atmospheric sciences, a kind-hearted and humorous person with empathy for the private lives of his colleagues and students, and a man who upheld the highest scientific standards for himself and for others. He made fundamental scientific contributions to a wide range of scientific topics in all parts of the atmosphere, from the mesosphere to the stratosphere and from the stratosphere to the troposphere. In particular, he was the first to describe the NO x -driven ozone depletion cycle in the stratosphere, he was among the first to develop the idea of chemical formation of ozone in the troposphere, he provided key concepts to explain the "ozone hole", and he made fundamental discoveries about the effects of biomass burning on the troposphere. Understanding and addressing the causes of anthropogenic air pollution and climate change were the driving motivations for his scientific work. In his work, he did not shy away from challenge and provocation. His work on smoke from fires after a potential nuclear war inspired new research on a concept now known as "nuclear winter". He also initiated the reopening of the debate on "geoengineering" - a concept now referred to as "climate intervention". He also brought the term "Anthropocene" to the popular debate. Moreover, he had a strong influence on atmospheric science through his educational role; there is a very large number of outstanding scientists who started their career with scientific work with Paul. In 2000, Paul was among the founders of the journal Atmospheric Chemistry and Physics, which was unique at the time in providing public discussion of published preprints as well as what we now call "open access" to published articles. Paul's work on human impacts on atmosphere and climate has had a profound impact on the environmental policies of many countries for decades. In the future, his work will continue to be a guide for generations of scientists and environmental policymakers to come.