Learning to see the invisible: discovery and measurement of ozone

Ozone is a key trace constituent of the atmosphere that is interesting for multiple reasons, including its ability to serve both as a screen against harmful solar radiation and as an aggressor against human health. However, methods for accurately detecting and measuring ozone were required before the behavior of ozone in the atmosphere and the effect of human activity on that behavior could be understood. This paper traces out the history of technologies and practices in ozone monitoring that have made this understanding possible, from nineteenth century chemical indicators to modern, laser-based detection technologies. Key insights include the importance of interactions between theorizing and observation in the process of scientific discovery, the importance of intercomparisons between different types of instruments, the way in which public policy concerns changed the pace and direction of ozone monitoring in the 1970s, and the importance of long-term environmental monitoring data to both improving our understanding of earth systems and protecting human health and the environment.