The analytical results of the acidity and buffering capacity of particulate matter sampled by aircraft over Chinese eastern coastal areas in March and early April 2002 are presented. The flight region covered the coastal areas from Zhuhai, Guangdong province, to Dalian, Liaoning province, and the northeastern coastal areas around Dalian, Liaoning province, with the later being the key flight areas. The results show that total suspended particles (TSP) generally appear to be acidic, having no buffering capacity for acidification; the acidity of TSP in northern areas is lower than that in southern areas, whereas the acidity of TSP in the bordering region of the northern areas and the southern areas is relatively high, the discrimination of the acidity of TSP in different areas could be up to more than 100 times. The acidity of particulate matter increases as its diameter decreases, indicating that fine particles have strong acidity. Both in northern areas and in southern areas, particulate matter with diameters larger than 11 ¿m has acidic buffering capacity, but particulate matter with diameters smaller than 2.1 ¿m appears to be acidic, having no buffering capacity. Although the pollution level of particulate matter at high altitudes is lower, its acidification is stronger than that at ground level. The regional acidification of particulate matter at high altitudes is an important reason why some areas in China suffer acidic precipitation.