[AAS11-P21] Wet removal mechanisms of black carbon observed in Tokyo and Okinawa
Keywords:Black carbon, Wet removal mechanism, Field observation
The size dependence of RE(DBC) showed remarkable differences for the observed 42 precipitation events (31 events in Tokyo and 11 events in Okinawa). The size dependence of RE(DBC) for BC-containing particles with DBC > 100 nm was successfully explained by the size dependence of Fccn(DBC), whereas the contribution of impaction mechanism can be dominant for particles with DBC < 100 nm. For DBC > 100 nm, when BC particles have relatively thick coating (shell/core ratio > 1.2), the RE(DBC) depended little on DBC and the major fraction of BC were removed via nucleation scavenging. On the other hand, when BC particles are nearly bare or have less coating, the RE(DBC) highly depended on DBC, and RE (i.e. Fccn) is more sensitive to the hygroscopiticy of coating materials and the maximum supersaturation of water vapor that BC particles would experience during moist convection process. Our results show that the coating thickness of BC is the key parameter controlling wet removal of BC, and indicate that for accurate simulation of vertical transport of BC from the boundary layer to the free troposphere, detailed modeling of microphysical properties of BC and atmospheric supersaturation is required especially for BC particles with thin coatings.