ALBERT

Description: [1]  The emission of black carbon (BC) from East Asia and its long-range transport strongly influence the mass concentration of BC (M BC ) over the western Pacific. However, reliable and long-term BC data are still limited in this region, especially at elevated altitudes. In this study, we present accurate measurements of M BC using a continuous soot monitoring system (COSMOS) at Happo, a remote mountain site at an altitude of about 1.8 km in Japan, from August 2007 to August 2009. The annual average M BC at Happo was about 0.26 ± 0.18 (1 σ) µg m -3 . The monthly average M BC values exhibited similar seasonal variations during both years, with minimum values in winter. Around 40 % of the air sampled at the site was of free tropospheric (FT) origin, with about 10% originating in North China (NC) origin, respectively. The M BC values for FT (0.24 µg m -3 ) and NC (0.23 µg m -3 ) air were representative of the M BC values (0.26 µg m -3 ) at 1.8 km height in the western Pacific, which are strongly influenced by BC emissions in North China. The M BC values calculated using a regional scale model reproduced well the M BC observed at Happo. The model predicted that BC transported from northern China alone contributed ~53% to the measured M BC , consistent with trajectory analysis. The comparison of model-calculated and observed M BC values indicates that the minimum values of M BC in winter were caused by the suppressed upward transport of BC over the Asian continent. Biomass burning in Siberia substantially increased M BC in the spring of 2008.