Illuminating atmospheric aerosols with fluorescence lidar: A new era in aerosol profiling? / Speaker: Benedict Gast (TROPOS)
Aerosol particles are key components in the climate system that shape Earth’s energy and hydrological budgets by interacting with clouds and radiation. Multi-wavelength Raman and polarization lidars are well-suited to characterize aerosol particles temporally and vertically resolved. In recent years, a new fluorescence lidar technique has been developed. Upon excitation with UV light, some aerosols exhibit fluorescence emission. Such organic aerosol types include, for example, wildfire smoke and any kind of biological aerosol particles like pollen. Because this laser-induced aerosol fluorescence is very weak and is located in the same wavelength range as the maximum of the solar spectrum, it can be measured only during nighttime.
In this webinar, we will introduce the basics of lidar remote sensing and the fluorescence lidar technique. The weak intensity of the fluorescence return signal poses high demands on the efficiency of the optical components that are used. Furthermore, measurement examples are shown to illustrate how the fluorescence lidar technique advances the lidar-based characterization of atmospheric aerosol particles. As the fluorescence process is unique to certain (biogenic) aerosol particles (air molecules, for example, do not exhibit fluorescence), the fluorescence technique enhances the detection sensitivity, especially of highly fluorescent aerosol types (like wildfire smoke), by providing particle-only information.
The fluorescence capacity, which describes the ability of a certain aerosol type to fluoresce, represents a new intensive quantity that greatly improves the aerosol typing with atmospheric lidar. Especially in the upper troposphere and lower stratosphere, it enables an unambiguous separation of wildfire smoke and volcanic sulfate, which is highly important for a better understanding of cirrus cloud formation processes. Furthermore, this technique allows retrieving aerosol particle information inside cloud layers, thus opening a new era of lidar-based aerosol profiling.