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

Abstract. Paul J. Crutzen was a pioneer in atmospheric sciences. At the same time, he was a kind-hearted, humorous person with empathy for the private lives of his colleagues and students, but also with 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 to the troposphere near the ground. In particular, he was the first to describe the NO_x -driven ozone depletion cycle in the stratosphere, he developed the first mechanisms for the chemical formation of ozone in the troposphere, he provided key ideas 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 man-made air pollution and climate change was the driving motivation for his scientific work. In his work he did not shy away from challenge and provocation. He pioneered the concept now known as “nuclear winter” and initiated the reopening of the debate on geoengineering. He also brought the term “Anthropocene” to the popular debate. 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, and also 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 policy makers to come.