Anomalies in Sea Spray Aerosol Optical Properties Detected by NASA High Spectral Resolution Lidar

Data from a NASA flight mission over the Azores Archipelago off the western coast of Africa are analyzed to identify anomalies in sea spray aerosol optical properties associated with ocean biological production. The weeklong flight campaign began October 11, 2012 and focused on the sampling of clean marine air with little contamination from other sources like African dust or continental pollution. The NASA High Spectral Resolution Lidar (HSRL) has a laser that emits a pulse at two wavelengths (0.532 and 1.064 μm) and a receiver that measures the backscattered radiation as a function of altitude. From this instrument, three important optical properties relevant to our study are derived: the aerosol lidar ratio, color ratio, and depolarization ratio, analysis of which can give insight into aerosol type, size, and shape respectively. To analyze the optical properties of aerosols within the marine boundary layer, one needs to accurately predict the boundary layer height and the presence of clouds in the optical path of the HSRL. Therefore, this study first introduces a new cloud-screening algorithm and then applies a boundary layer detection algorithm to filter the aerosol sample. Our analysis for the cloud free regions revealed statistically significant anomalies in particle depolarization ratio (δ>10%) that were well correlated with surface chlorophyll-a concentrations (R≈0.5) detected by NASA's MODerate Imaging Spectroradiometer (MODIS). Other parameters such as the lidar ratio and color ratio that are influenced by the aerosol size distribution and physiochemical properties will also be discussed. This study suggests that HSRL is suitable for exploring the effects of ocean biological production on clean marine aerosol optical properties.