Aerosol Transport to the Boundary Layer in a Post- Frontal Air Mass

Lynn Russell, Don Lenschow, and Krista Laursen

Aerosol Characterization Experiment 1 employed a Lagrangian approach to study chemical and microphysical processes in the boundary layer. In the Lagrangian B experiment, the dynamics of the post-frontal air mass were characterized in an initial flight, then a constant-level balloon was launched and the air mass in which it was carried was tracked for three consecutive 8-hr flights during a 33-hr period. The boundary layer was capped by a weak inversion near 500 m, with a transition layer above extending to over 2000 m. The air was cloud free until the third Lagrangian B flight, when scattered cumulus appeared near the top of the boundary layer. In-situ measurements of aerosol particles above the boundary layer revealed high concentrations of nucleation-mode aerosol at the beginning of the first Lagrangian B flight while less than 50 cm^(-3) nucleation-mode particles were present in the boundary layer. During the second and third flights aerosol particles of this size were mixed into the boundary layer. The rate of entrainment of aerosol into the boundary layer was calculated and compared to estimates of the flux calculated from divergence measurements. Initial calculations show good agreement during the first two flights of Lagrangian B, but interpretation of the third flight is complicated by the appearance of clouds.