Retrieving Vertical Profiles of Aerosols and Their Cloud Nucleating Properties Using a Micropulse Lidar

Aerosol-cloud interactions remain the largest uncertainty in modeling the anthropogenic forcing of the climate system. Reducing this uncertainty will require more detailed information on the vertical distribution of aerosols capable of acting as cloud condensation nuclei (CCN) and ice nucleation particles (INPs). Here we demonstrate how a portable miniMPL (Droplet Measurement Technology mini Micropulse Lidar) combined with surface-based aerosol size distribution measured with SMPS (TSI Scanning Mobility Particle Sizer) and POPS instruments (Handix Scientific Portable Optical Particle Spectrometer), CCN concentration measured with CCN counter (Droplet Measurement Technology), and INP freezing temperatures measured with custom built apparatus can be used to generate vertical profiles of aerosols and their cloud-forming properties. The vertical profiles of the backscatter coefficient are first retrieved using the Fernald inversion method. Assuming a uniform dry aerosol size distribution and composition below clouds, the average aerosol backscatter coefficient is calculated using surface aerosol measurements and a T-matrix code. The vertical profile of the backscatter coefficient is then used to derive the aerosol concentration profiles. Next, the surface measurements of the critical supersaturation and temperature requirements for CCN and INP activation are compared to ambient humidity and temperature to assign cloud-forming properties to the vertical aerosol profiles. Finally, we demonstrate the utility of this method by applying it to measurements collected during the recent TRacking Aerosol Convection interactions ExpeRiment (TRACER) field campaign.