Vertical 2-μm Heterodyne Differential Absorption Lidar Measurements of Mean CO2 Mixing Ratio in the Troposphere

Abstract

Vertical mean CO2 mixing ratio measurements are reported in the atmospheric boundary layer (ABL) and in the lower free troposphere (FT), using a 2-?m heterodyne differential absorption lidar (HDIAL). The mean CO2 mixing ratio in the ABL is determined using 1) aerosol backscatter signal and a mean derivative of the increasing optical depth as a function of altitude and 2) optical depth measurements from cloud target returns. For a 1-km vertical long path in the ABL, 2% measurement precision with a time resolution of 30 min is demonstrated for the retrieved mean CO2 absorption. Spectroscopic calculations are reported in details using new spectroscopic data in the 2-?m domain and the outputs of the fifth-generation Pennsylvania State University?National Center for Atmospheric Research Mesoscale Model (MM5). Then, using both aerosols in the ABL and midaltitude dense clouds in the free troposphere, preliminary HDIAL measurements of mean CO2 mixing ratio in the free troposphere are also presented. The 2-?m HDIAL vertical measurements are compared to ground-based and airborne in situ CO2 mixing ratio measurements and discussed with the atmospheric synoptic conditions.