Synergistic Retrieval of Aerosol Chemical Composition Profiles from Airborne Multiwavelength Lidar and Polarimeter Observations

Understanding the vertical distribution of aerosol chemical species is vital for assessing their impact on climate, air quality, and human health. Airborne measurements, providing high-resolution vertical profiles, capture local and regional variability, which is often missed by ground-based or satellite observations. Such measurements are essential for validating retrieval methodologies and improving chemistry–transport models. Specifically, airborne campaigns equipped with lidars and polarimeters offer unique observational constraints on aerosol optical, microphysical, and chemical properties, supporting the refinement of advanced retrieval algorithms.

In this context, we have developed a new synergistic approach for retrieving vertically resolved aerosol chemical species simultaneously present in the atmospheric column by jointly exploiting lidar and polarimeter measurements. This method, termed Aerosol Chemical Profiling (AEROCHEMPro) is implemented within the GRASP (Generalized Retrieval of Atmosphere and Surface Properties) inversion framework. While AEROCHEMPro has previously been evaluated using synthetic lidar–polarimeter observations, the present study reports its first application to real airborne measurements. The AEROCHEMPro retrieval exploits multispectral lidar capabilities to discriminate aerosol modes and their associated chemical composition: a fine mode containing black carbon, brown carbon, inorganic salts, and aerosol water content; a coarse desert dust mode composed of iron oxide and quartz; and a second coarse mode consisting of sea salt and aerosol water content. By providing a statistically optimized estimate within a continuous solution space, the method delivers detailed vertical distributions of aerosol species, strengthening the link between remote sensing observations and aerosol chemical composition. This capability is critical for understanding aerosol chemical evolution and for evaluating numerical simulations produced by chemistry–transport models.

In this work, the AEROCHEMPro methodology is applied to airborne measurements acquired by two advanced instruments operated onboard the same aircraft: the second-generation High Spectral Resolution Lidar-2 (HSRL-2) and the Research Scanning Polarimeter (RSP). HSRL-2 provides high-accuracy active remote sensing of aerosol at 3 wavelengths, with high-spectral and depolarization capabilities, while RSP, a passive multi-angular polarimeter, measures radiance and linear polarization across nine spectral bands from the visible/near-infrared to the shortwave infrared. The combined use of these complementary datasets demonstrates the capability of AEROCHEMPro to retrieve vertically resolved concentrations of multiple aerosol chemical species, as well as type-specific aerosol chemical, optical, and microphysical properties from airborne observations, highlighting its potential for broader application to future multi-sensor remote-sensing studies.