| Polycyclic aromatic hydrocarbons (PAHs) are a set of persistent organic pollutants which widely exist in the environment. Researches have shown that, PAHs are carcinogenic, teratogenic and mutagenic, and they are a big threat to the ecological environment and our human health. PAHs thus have attracted extensive attentions of researchers worldwide. The incompletely combustion of fossil fuels and straws are main sources of PAHs. The calculation of PAHs emission inventories can help figure out main PAHs emission sources. PAHs were usually emitted into the atmosphere in gaseous or particulate forms, and then they migrated to water, soil and other media by wet and dry deposition and affected the human society through the processes. The study of mechanisms of the migration and transformation processes of PAHs can provide theoretical data for the city management and decision making. This study used emission-factor-method from the bottom to the top to calculate emission inventories of six typical cities in the Yangtze River Delta (including Shanghai, Suzhou, Wuxi, Changzhou, Hangzhou, and Jinxing). Our analyses include changes of the main energy consumption, the main emission sources, emission spectra, emission density and emission trends. Emission data and GDP of each city were fitted. Selecting Shanghai as the research object, the urban multimedia model has been used to simulate the fate of PAHs in urban multimedia environments and analyze their behavior characterization of transfer, transformation and distribution. PAHs emission of Shanghai has been predicted as well. Moreover, ecological risk assessment of PAHs has been analyzed and suggestions for the urban development have been put forward.Results showed that the total PAHs emission was 447.8 t, including 7 kinds of carcinogenic PAHs (60.06t) in Shanghai in 2012. Coking coal and domestic coal combustions (56.0%) were main sources of PAHs emissions. According to the PAHs emission spectrum, NAP occupied the largest proportion, followed by PHE, while high molecular weight compounds emissions were less. PAHs emissions of Shanghai generally presented a trend of decline.Total emissions of PAHs in Suzhou, Wuxi, Changzhou, Hangzhou and Jiaxing in 2012 were 103.67 t,44.27 t,46.31 t,57.19 t,32.67 t, respectively. The main emission sources in Suzhou, Wuxi, and Changzhou were natural gas, domestic coal, and coking coal. Hangzhou’s major emission sources were natural gas; coal and oil refinery. Jiaxing’s PAHs mainly came from domestic coals, rice straws and the oil refinery. PAHs emission density of Shanghai was the largest among the six cities (70.6 kg/km2). It was 5.8 times of the national data. But it was lower than that in 76 cities whose populations were more than one million. Suzhou’s PAHs emission density was similar to the national average level. The rest of cities were slightly lower than the national average level, and Hangzhou was the lowest.By using the urban multimedia model, the fate of PAHs has been simulated. Results showed high concentrations of PAHs were found in soil and in the organic films. In contrast, the concentration of PAHs in the atmosphere was low. Considering the quantity of PAHs alone, soils and sediments have the highest PAHs content, while organic films have the lowest PAHs content. After migration and transformation processes in the environment, PAHs’main destinations were soils and sediments.The forecast of PAHs emissions in 2020 in Shanghai would be 356.57 t. NAP will still account for the largest fraction (115 t). Compared to 2012, emissions of coking coal showed a downward trend. Emissions of gasoline and diesel oil would be increased on the contrary. According to the concentration results of the simulation model of MUM, The TEQ value of PAHs of Shanghai is 0.616ng/m3, which is in the scope of national standards (1 ng/m3). Considering the calculation error and its harm, Shanghai still faces a great ecological risk. |
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