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Title: Study of atmospheric trace metals in particulate matter, dry and wet depositions, and mosses in the Pearl River Delta region
Authors: Lee, Siu-lan
Degree: Ph.D.
Issue Date: 2007
Abstract: The study of trace metals in the atmosphere is important due to the critical effects of trace metals on human health and the geochemical balance of the ecosystems. Trace metals in particulate matter are important phases in the air environment, which can be transported and deposited to places far away from their sources in the terrestrial environment. In the past few decades, China has undergone drastic economic development, leading to the rapid industrialisation and urbanisation in many parts of the country. The Pearl River Delta region (PRD) is the most important economic zone in South China region, and in recent years, it has been susceptible to severe atmospheric pollution from rapid industrial development and urbanisation process in the region, imposing mounting pressure to the regional environmental quality. The objective of this study was to investigate the current level of atmospheric trace metal pollution in urban and rural areas of the Pearl River Region over one year period of measurement, which would provide insights to the sources and temporal and spatial distributions of trace metals in the air of the PRD region. The research project also examined the transport of particulate trace metals and their pathways of deposition (by dry and wet depositions) in the PRD region, which is important in strategic environmental planning and pollution control. The potential use of mosses in bio-monitoring of air quality in the PRD region was also evaluated. A few moss species were identified to be used in monitoring of atmospheric trace metal pollution in subtropical areas. This study focused on an integrated study of trace metals in particulate matter, dry and wet depositions and mosses in the PRD region. Sampling of aerosols, and dry and wet depositions was conducted over one-year period from Dec 2003 - Jan 2005, and mosses during Jan 2003 in the Nanling Mountains, and May 2004 in Dinghu Mountain. Moreover, PM2.5 samples collected from Guangzhou area of the PRD region in an annual sampling campaign during May 2005 - May 2006. The samples were analysed for the concentrations of major elements (Al, Fe, Mg and Mn) and trace metals (Cd, Co, Cr, Cu, Ni, Pb, V and Zn), and for Pb isotopic composition. The dataset collected in various urban and rural areas in the PRD region provided comprehensive information of the atmospheric trace metal pollution both locally and in a regional context. High concentrations of trace metals, especially Cd, Pb, V and Zn, were observed in the urban and suburban areas of Guangzhou, showing significant atmospheric trace element pollution. Distinct seasonal patterns were observed in the heavy metal concentrations of aerosols in Hong Kong, with higher metal concentrations during the winter monsoon period, and lower concentrations during summertime. The seasonal variations in the metal concentrations of the aerosols in Guangzhou were less distinct, suggesting the dominance of local sources of pollution around the city. The Pb isotopic composition in the aerosols of Hong Kong had higher 206pb/207pb and 208pb/207pb showing the influence of the northern inland areas of China and the Pearl River Delta (PRD) region, and lower 206pb/207pb and 208pb/207pb ratios in summer. indicating the influence of Pb from the South Asian region and from marine sources. The back trajectory analysis showed that the enrichment of heavy metals in Hong Kong and Guangzhou was closely associated with the air mass from the north and northeast that originated from northern China, reflecting the long-range transport of heavy metal contaminants from the northern inland areas of China to the South China coast. The high PM2.5/TSP ratios of trace metals such as Cd, Cu, Ni, Pb and V in urban areas of Guangzhou showed that the metals were predominately associated with finer fractions, and relatively low ratios were depicted for Co, Cr and Zn, probably reflecting greater influences from natural sources. Elevated dry and wet deposition fluxes were found in the urban and rural areas of the inland PRD area (near Guangzhou), showing severe atmospheric pollution in the region, especially for Cd, Pb and Zn. Distinguished temporal variation were observed in the dry and wet depositions for trace elements in the urban and rural areas, but those in suburban areas was less distinct. Higher dry deposition flux of Zn was found in the urban areas during the winter season, probably due to the influx of pollutants to the PRD region due to the winter monsoon system and the relatively dry condition in the winter time. The wet deposition fluxes of Co, Cu and Zn in the urban areas were observed to be higher in summer, attributed to a greater scavenging effect by rain. The mode of deposition was found to vary for different elements. Aluminium, Fe and Cr were found to be mainly deposited as dry depositions, and Cd, Co, Cu, Mg, Mn and Zn were primarily deposited as wet depositions, during both the winter and summer seasons. The predominant pathway for Pb and V was dry deposition during winter and wet deposition during the summer season. The Pb isotopic ratios of most dry and wet deposits, during both the winter and summer seasons, were found to be similar to the anthropogenic sources in the PRD region, such as the Pb ore, industrial and vehicular emissions. The input of Pb could be originated from various anthropogenic sources in the PRD region. Some of the dry deposits in the coastal areas were found to have Pb isotopic composition similar to the Vietnam aerosols, showing that the long range transport of pollutants during the summer season from South Asian countries may have significant effect on the atmospheric dry depositions in the coastal PRD area. The suitability of the moss Hypnum plumaeforme as a new biomonitor of atmospheric trace element pollution in southern China was also evaluated. The results showed that the moss had a good capacity to absorb and retain heavy metals such as Cd, Co, Cu, Cr, Pb, V and Zn. The northern part of the Nanling mountain range was found to have more trace elements than the southern range, possibly reflecting the long range transport of pollutants from northern China. The elemental concentrations of the mosses in the northern range were found to be well correlated with elevations. The concentrations of heavy metals decreased as elevations increased, and became relatively constant above 1100 m a.s.l. The Pb isotopic compositions indicated that atmospheric inputs of Pb in mosses were mainly derived from anthropogenic sources, including vehicular emissions and Pb used in local industries. A comparative study was conducted on the metal uptakes of different moss species, including Hypnum plumaeforme, Leucobryum chlorophyllosum, Pogonatum contorium, Thuidium tamariscinum and Bazzania tridens. The results showed that the moss species, Hypnum plumaeforme and Thuidium tamariscinum were suitable to be used as biomonitors of trace metals in the South China region, as they were found to have higher uptakes of most trace metals compared with other species, which has great potential use in the future monitoring of atmospheric trace metal pollution in the South China region and other subtropical areas.
Subjects: Hong Kong Polytechnic University -- Dissertations.
Trace elements -- Environmental aspects -- China -- Pearl River Delta Region
Pages: xix, 223, [27] leaves : ill. (some col.) ; 30 cm.
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