Aircraft Measurements of Upward Transport of Black Carbon Over East Asia in Spring 2009

A wet removal is considered to be a major loss process of black carbon (BC) aerosols from the atmosphere. However, a quantitative understanding of this process is still limited due to the insufficient observations of BC in the free troposphere (FT). We conducted aircraft observations of BC over East Asia in March-April 2009, together with carbon monoxide (CO). The concentrations of BC and CO were greatly enhanced in air parcels sampled at 3-6 km over the Yellow Sea in March, associated with upward transport due to the cyclonic activity over the northeastern China. However, the BC-to-CO (BC/CO) ratio was greatly reduced in the plumes uplifted to 5-6 km over the southern China in April. The large difference in the BC/CO ratios was related to the large difference in the amounts of precipitation that air parcels had been influenced during the vertical transport. We derived the fraction of BC removed from the atmosphere during transport of air parcels (removal efficiency of BC) and the accumulated precipitation along the trajectories (APT) using the entire data sets obtained in the FT. The median removal efficiencies of BC for air parcels uplifted over northern China were 14% (sampled at 2-4 km) and 51% (4-9 km). They were much greater for those uplifted over southern China, namely 31% at 2-4 km and 68% at 4-9 km. Correspondingly, the median APT was smaller for the air parcels uplifted over northern China than those uplifted over southern China. On average, the removal efficiency of BC increased with the increases in the APT, demonstrating the importance of the precipitation in controlling transport of BC from the planetary boundary layer to the FT over the Asian continent.