Aerial observation was conducted during spring (March–April) 2008 over the East China Sea to analyze the transport of atmospheric pollutants from East Asia and the transformation processes during transport. Concentrations of sulfur dioxide (SO2), ozone (O3), total reactive nitrogen (NOy), carbon monoxide (CO), and black carbon (BC) were measured on board the aircraft, and chemical analyses of aerosols were performed subsequently by high-volume filter sampling of aerosols and ion chromatography and inductively coupled plasma-mass spectroscopy (ICP-MS) analyses. The distributions of gases and aerosols clearly suggested a layered structure to the air mass, in good agreement with predictions of the CFORS (Chemical weather FORecast System) model. The non-sea-salt (nss)-[sulfate (SO42–)]/([SO2] + nss[SO42–]) ratio value, which increased from north to south along the aircraft flight track, indicated oxidation of SO2 to form sulfuric acid during transport. In addition, pronounced chlorine loss suggested that substantial production of acidic substances occurred in the air mass as it moved away from China. The negative correlation between the Cl–/Na+ ratio and the nss–sulfate concentration suggested that the reaction of sulfuric acid with sea salt was the main cause of the strong chlorine loss. On 28 March a very clear layered structure of the air mass was observed that could be clearly explained by the CFORS computer simulation model. Therefore, here the observation results obtained on 28 March 2008 are reported.