Aerosol Vertical Transport, Exchange, and Transformation in Maritime Southeast Asia: Observations and Implications from CAMP2Ex and PISTON

Unlike other intercontinental aerosol events, major smoke and pollution ejections from maritime Southeast Asia are remarkable in that the dominant advection pathway occurs over 1000s of kilometers within the Planetary Boundary Layer (PBL) and lower free troposphere. Indeed the majority of a column aerosol optical depth (AOD) is contributed by particles within and just above the PBL. There are also relatively few observations of mid tropospheric aerosol detrainment. Using the complement of Cloud, Aerosol and Monsoon Processes Philippines Experiment (CAMP2Ex) and Propagation of Intra-Seasonal Tropical OscillatioNs (PISTON) airborne, ground, ship and space-based observations and modeling, we elucidate how smoke from Borneo and pollution from Asia are transported into the tropical and subtropical Western Pacific. Each of the tools has its own capabilities and shortcomings in piecing the system together. Models and dropsondes demonstrate that strong vertical wind shear within the Southwest Monsoon system is the dominant player in dictating vertical distribution. Lidar and cloud stereography techniques then show how the aerosol layer is closely related to PBL cloud and congestus vertical distribution. Efficient precipitation scavenging in the tropical marine convection also inhibits aerosol particle detrainment, but gas phase tracers are nevertheless observed detraining from both shallow and deep convective clouds. Within the PBLs mixed layer, entrainment zone and free troposphere interface, diurnal volumetric variability in concentration and particle and trace gas attributes were observed, providing clues to lower atmosphere air motions and cloud processing. Observations show that model simulations struggle to correctly portray cloud related boundary layer-free tropospheric exchange.