Biomass Burning Plumes in the Vicinity of the California Coast: Airborne Characterization of Physicochemical Properties and Spatiotemporal Features

This study characterizes in situ airborne properties associated with biomass burning (BB) plumes in the vicinity of the California coast. Out of 231 total aircraft soundings in July-August 2013 and 2016, 81 were impacted by BB layers. A number of vertically-relevant characteristics of BB layers are summarized in this work (altitude, location relative to cloud top height, thickness, number of vertically adjacent layers, inter-layer distances) in addition to differences in vertical aerosol concentration profiles due to either surface type (e.g., land or ocean) or time of day. Significant BB layer stratification occurred, especially over ocean versus land, with the majority of layers in the free troposphere (FT) and within 100 m of the boundary layer (BL) top. Aerosol size distribution data are summarized below and above the BL, with a notable finding being enhanced concentrations of supermicrometer particles in BB conditions. Aerosol composition data revealed the dominance of organics in the FT in BB and non-BB conditions, with evidence for secondary production of both inorganic and organic species in BB conditions as a function of distance from fire source up to 450 km. Comparisons between aircraft data and the Navy Aerosol Analysis and Prediction System (NAAPS) model motivate the need for improved meteorological and aerosol modeling with higher spatiotemporal resolution, and improved physical representation of the boundary layer processes necessary for capturing narrow BB plumes, such as those observed by the California coast.