Current trends and future outlook in spectroscopic monitoring of the atmosphere

Spectroscopy has long played a central role in determining and monitoring the composition of the atmosphere. We outline how current scientific and sociopolitical concerns-whether alarm at anthropogenic climate change, exposure to air pollution, or fundamental scientific questions about atmospheric processes and transformations-motivate the need for better and more extensive measurements of atmospheric composition. We present a brief history of spectroscopic observations of the atmosphere and describe topics that are current focal points of atmospheric research. Technological advances that hold promise for spectroscopic applications are described, including light sources like supercontinuum sources and mid-infrared sources like quantum cascade lasers, interband cascade lasers and frequency combs. Also covered are unmanned aerial systems, which have much potential for observations in settings where traditional airborne measurements are impossible. Finally, we reflect on the role and future outlook for atmospheric spectroscopy.