Estimation method for contribution of emission to trace metal concentrations in urban atmosphere based o
Principal Research Results Background Clarification of the contribution of emission sources to trace metal concentrations in the atmosphere is useful for an accurate evaluation of the environmental impacts of trace metals to efficiently proceed with emission control measures. However, the emission sources of trace metals are often unknown. Even if they are known, the substantial fluctuation of the concentrations in exhaust gas make it generally difficult to accurately measure such concentrations. Consequently, the conventional chemical element balance method which relies on the mass balance of marker elements to estimate the contribution of emission sources has failed to produce reliable data except for some elements. Meanwhile, an estimation method for lead has been studied based on the lead isotope ratios ＊1 which characterizes each specific emission source and which can be measured with high accuracy. Objectives To propose an estimation method which is applicable to the urban atmosphere in Japan for the contribution of emission sources to trace metal concentrations in the atmosphere based on the lead isotope ratios. Principal Results 1. Emission Sources of Lead in Urban Areas The lead isotope ratios in the atmosphere in A City, selected as the urban atmosphere study site, were almost constant regardless of fluctuations of the lead concentration (Fig. 1). The established values were identical to those measured in seven cities in Japan as well as those of fly ash produced by refuse incineration (Fig. 1). These results suggest that lead in the urban atmosphere in Japan is mainly discharged by refuse incineration with the isotope ratios being fairly constant except in certain areas which are affected by specific local emission sources. 2. Correlation Between Lead Concentration and Other Trade Metal Concentrations (Cd, Cr, Cu, Mn, Ni and Zn) in Urban Atmosphere The study on the relationship between the lead concentration and other trace metal concentrations in the atmosphere in A City and at 16 stations of the National Air Surveillance Network (Environment Agency, Japan) found that the emission ratios of lead and other trace metals from refuse incineration plants are roughly identical nationwide (Fig. 2). Accordingly, the contribution of refuse incineration to trace metal concentrations can be estimated by comparing the trace metal/lead ratios (concentration ratios) in dust from refuse incineration plants and the atmosphere. 3. Proposal of Estimation Method for Contribution of Emission Sources to Trace Metal Concentrations Based on Lead Isotope Ratios Based on the consideration that lead in the atmosphere originates from refuse incineration and other sources, a new estimation method for the contribution of emission sources to trace metal concentrations using the contribution of lead from such sources, determined by the lead isotope ratios, is proposed (Fig. 3). This method can be used to evaluate the environmental impacts of trace metals in (1) areas surrounding specific emission sources of lead (coal-combustion and lead smelting, etc.) and (2) areas affected by lead transported for a long distance from the Chinese continent (emission of lead through the use of leaded gasoline and the combustion of coal, etc.) Future Developments To investigate the applicability of the new estimation method in areas along the Sea of Japan and also in large cities. Main Researcher: Masahiro Sakata Research Fellow, Atmospheric Science Department, Komae Research Laboratory Reference “Estimation Method for Contributions from Emission Sources to Trace Metal Concentrations in Urban Atmosphere Based on Lead Isotope Ratios,” CRIEPI Report No. T97050, May, 1998 (Japanese only) ＊1：The lead isotope ratios ( 206 Pb/ 207 Pb and 206 Pb/ 208 Pb, etc.) of lead ores vary depending on the time of ore formation as well as the geological conditions. Lead released into the atmosphere has a characteristic value reflecting the isotope ratios of the original lead ores. It is, therefore, possible to estimate the contribution of a specific source to lead concentration by accurate measuring. 30 Estimation Method for Contribution of Emission Sources to Trace Metal Concentrations in Urban Atmosphere Based on Lead Isotope 3. Environment - Local Environment 31 2.5 2 1.5 1 0.5 0 0.5 0.48 0.46 0.44 0.42 0.4 020406080100 1.2 1.18 1.16 1.14 1.12 1.1 0 40 80 120 160 200 240 206 Pb／ 208 Pb= 0.47478 ＋ − 0.00064 206 Pb／ 207 Pb= 1.1570 ＋ − 0.0017 206 pb／ 207 pb 206 pb／ 208 pb F1 F2 f1 f2 Lead Concentration (ng/m 3 ) 206 Pb/ 207 Pb Cadmium Concentration (ng/m 3 ) 206 Pb/ 207 Pb Fig. 1 Relationship between Lead Concentration and Lead Isotope Ratios in Atmosphere ● ○ Lead Isotope Ratios (measured) ■ □ Mean Ratios in Atmosphere in 7 Cities (n = 18, from literature) ▲ △ Mean Ratios of Fly Ashes from Refuse Incineration (n = 7, measured) While the lead concentration in the atmosphere substantially fluctuates due to different meteorological conditions, the lead isotope ratios in the atmosphere remain almost constant, presumably because of the mixing and uniformatization of a large amount of waste containing lead in refuse incineration plants. Fig. 2 Correlation between Lead and Cadmium Concentrations ● Annual Mean Values at 16 Stations of the National Air Surveillance Network (from literature) ＊ Mean Value at 7 Refuse Incineration Plants (from literature) The ratios of the Pb and Cd concentrations in the atmosphere obtained by the National Air Surveillance Network are almost identical to those of the study site in A City and dust from refuse incineration, implying that almost of the total amount of Cd in the atmosphere originates from refuse incineration as in the case of Pb. Fig. 3 Schematic Drawing of Estimation Method for Contribution of Emission Sources to Trace Metal Concentrations Atmosphere in 7 Cities Fly Ashes from Refuse Incineration Lead Concentration (ng/m 3 ) Dust from Refuse Incineration (Cd/Pb = 0.029) Atmosphere in A City (Cd/Pb = 0.025) Dust from Refuse Incineration Dust from Other Sources Lead Concentration Trace Metal Concentrations Lead Concentration Trace Metal Concentrations Emission Sources Mixing Airborne Dust Contribution Estimation Process Atmosphere Lead Concentration Trace Metal Concentrations Contribution of Trace Metals f1 f2 Contribution of Lead F1 F2 Lead Isotope Ratio Trace Metal/Lead Concentration Ratio . measuring. 30 Estimation Method for Contribution of Emission Sources to Trace Metal Concentrations in Urban Atmosphere Based on Lead Isotope 3. Environment. Komae Research Laboratory Reference Estimation Method for Contributions from Emission Sources to Trace Metal Concentrations in Urban Atmosphere Based on