Lead isotope ratios in ambient aerosols from Taipei, Taiwan: Identifying long-range transport of airborne Pb from the Yangtze Delta

A total of 142 sets of PM10 and PM2.5 aerosol particles collected from Taipei during a period from April 2003 to February 2004 were determined for atmospheric Pb concentrations. Among these samples, 77 sets of samples representing four seasons were selected for measuring Pb isotopic compositions to determine the relative contributions of various pollution sources. Results reveal an evident seasonality of high winter and low summer Pb concentrations, resembling those observed in Shanghai, China as well as many East Asian countries. Together with synoptic atmospheric conditions analysis, the seasonal pattern is attributable to the impact of long-range transport of Pb-rich anthropogenic aerosols from the Chinese pollution outflows in the northeast monsoon and to the effective removal by wet deposition in summer. Results of 206Pb/207Pb and 208Pb/207Pb isotope ratios show a minimum in summer, thereafter increasing progressively to fall to winter and reaching a maximum in spring. The summer values are similar to that of tunnel particles for 206Pb/207Pb ratio but dissimilar to that of tunnel particles for 208Pb/207Pb ratio. Here summer aerosols may represent a local pollution-influenced case, and tunnel particles represent a vehicle exhaust source for atmospheric Pb. Therefore apart from vehicle emissions of Pb for Taipei aerosols, other sources such as incineration, metalliferous industry and coal combustion of fire power plants need to be taken into account. The winter and spring Pb isotope ratios are quite comparable with those measured in China, especially Shanghai in the Yangtze Delta. Again this demonstrates northern Taiwan has already been affected by continental pollution of long-range transport during the northeast monsoon season beginning in early fall and ending in late spring. By employing a two end-member mixing model based on the assumption that the summer case represents the local source end-member, the relative contributions of long-range transport for anthropogenic Pb have been estimated to be 40% in fall, 50% in winter, and 75–85% in spring.