Aircraft observations of natural and anthropogenic substances during the Asian outflow over the East China Sea in the winter of 2000

To investigate the impacts of anthropogenic and natural substances transported from the Asian continent in winter on the abundance of atmospheric aerosols and cloud condensation nuclei (CCN), in the planetary boundary layer (PBL) and free troposphere (FT) over the receptor region, aircraft observations of number concentrations of aerosol and CCN as well as sulfur dioxide (SO₂) were carried out over the East China Sea (ECS) during the Asian Atmospheric Particulate Environmental Change Experiment 1 (APEX-E1) in December 2000. Reanalysis data of meteorology (ERA5) and aerosols (MERRA-2) were used to interpret the observation results. The results on December 23 were characterized by the highest concentrations of all parameters including CCN more than 400 cm⁻³ at supersaturation (SS) of 0.40 % and SO₂ (>4 ppbv) in the PBL under relatively fresh polluted air, due to rapid transport of anthropogenic and natural substances through the PBL by subsidence of air and strong winds behind cold front. On December 24, anthropogenic pollutants and dust particles were transported into the FT by ascent of air associated with a low-pressure system over the Asian continent. SO₂ and coarse mode aerosols were higher than those in the PBL and CCN concentration was more than 100 cm⁻³ (SS = 0.40 %). In addition, this kind of ascent of air to the lower FT occurs several times on average in December. Our results suggest that in addition to traditional trajectory analysis, it is necessary to incorporate the history analysis of vertical transport and wind-induced aerosol emissions along the transport pathway.