| Polycyclic aromatic hydrocarbons (PAHs) are a kind of persistent organic pollutants (POPs) with great ecological and health risks, which are widely spread in the environment. Researchers have found they are difficult to be degraded and are carcinogenic, teratogenic and mutagenic. In 1973, American scholars showed that the cancer risk of mortality will increase by 5% with the ascending concentration of 0.1μg/100m3 BaP in the atmosphere. Epidemiological survey research demonstrated that the air contains high concentrations of carcinogenic PAHs in some heavily polluted area where the prevalence of lung cancer is significantly higher than that in other areas. Those high cancer risks were closely related with the high exposure of PAHs. In 1976, International Agency for Reserch on Cancer (IARC) studied the 94 kinds of compounds that cause cancer in laboratory animals. It was found that there are 15 kinds of PAHs compounds, among which BaP is the strongest carcinogenic substance. Big city as a complex system is connected with the physical environment, cultural environment and community economy. City is also a region unit closely related to human life and health. So far, urbanization is the most active form of human activities and interference and is also the driving force of the key environmental changes. Recently, with the acceleration of urbanization process and the rapid development of transportion, urban air pollution become more and more serious. Until now, PAHs pollution in the atmosphere has increasingly become a hot issue.Shanghai, as the center of the Yangtze River Delta city, with highly developed commerce and industry, is a habitat with concentrated human activities. In my paper, Shanghai was chosen as the study area. Atmospheric deposition was collected throughout a year at eight sampling sites, then, we systematically analyzed the pollution characteristics of PAHs in the particulate phase and dissolved phase, source distribution and deposition fluxes in the atmospheric deposition. We discussed the influence of weather conditions on concentrations of PAHs every month. To quantitatively analyze the sources of PAHs, a variety of research methods were used. While, we also used RQ-TEQ complex models to assess the ecological risk of each sampling site.Atmospheric deposition of pollutants in the environment is an important migratory process of the earth’s surface environment and has great potential threat. In the environment, part of the PAHs in the atmospheric deposition from the atmosphere into the surface environment system, can play an important role in reducing air pollution. At the same time. PAHs sedimented into the land surface through the food chain, and the enrichment effect of PAHs in the trophic leves, has a significant impact on the ecosystem. What’s more, some fine particles can stay short or long periods and suspend in the atmosphere. The extreme atmospheric pollution incidents were emerged. It has a great impact on the industrial and agricultural production, health and ecological environment. Two means of PAHs migration produced more far-reaching impact on human. Because of the serious situation in Shanghai air pollution, atmospheric PM2.5 samples were collected at the same time, while acquiring atmospheric deposition. Characteristics of PM2.5 and PAHs were discussed. Two models were used to explain the potential sources of PAHs and quantitatively analysize source conctribution of PAHs. We used Spearman correlation to discover the coefficient of correlation between PM2.5, PAHs and related meteorological factors. The study found that this correlation was much more complex. In each quarter, the correlations were quite different. The ILCRs model was used to estimate the cancer risk of ingesiton, dermal contact and inhalation, reference to international standards, and the health-risk results were compared among different seasons. Finally, we used HYSPLIT model for reference and simulated the 48h backward trajetories of PM2.5, then, adopt mathematical algorithms to calculate the potential contribution area. In the study, we focused on atmospheric deposition of PAHs and PM2.5 to figure out the various functional areas of atmospheric deposition and clearly comprehend migration and variation of PM2.5 and PM2.5-bound PAHs, hoping to provide a reliable scientific basis for the Shanghai environmental protection and atmospheric environment, ultimatly.The concentration of 16PAHs measured in the atmospheric deposition in Shanghai was 0.458-21.013 μg/L, the mean value was 5.221μg/L. Atmospheric deposition in the dissolved phase was in the range of 0.151 to 0.857 μg/L, the average was 0.380 μ g/L. While, 16PAHs in particle phase ranged from 0.275 to 20.45μg/L, with an average of 4.840 μ g/L. Compared to the pollution status at home and abroad, the range of dissolved phase PAHs was small. However, the PAHs concentration of dissolved phase was roughly equal to the domestic and foreign concentration, the particulate phase PAHs were significantly higher than cities abroad and the overall levels of pollution were moderate. For the overall function zone, the atmospheric deposition of PAHs showed a general trend as: industrial zone> urban zone>suburban zone. Particulate phase and dissolved phase exhibited similar variability.In the annual atmospheric deposition samples, the fourth-ring PAHs were detected as the highest concentration of PAHs in the particle phase, among which Fl, Py were the highest. The ratio of the concentration of the 2-3 ring is lower, of which the total was 14.25%～61.60% with the average of 31.61%. On the whole, the solution phase was the lowest in 5-6 ring and the highest in the 2 and 3 ring. From the change in terms of time scale,2-3 ring PAHs have significantly increased and 5-6 ring PAHs proportion has decreased. The proportion of high and middle ring increased in autumn.The ratio of low ring decreased obviously and otherwise with high ring in winter. From winter to summer, the high and middle ring decrease and low ring increased in solution phase. From summer to winter, the trend is on the contrary.The atmospheric deposition fluxes of E 15PAHs was 0.338-15.491μ g/(m2·d), with a mean value of 3.849 μg/(m2·d). Atmospheric deposition fluexs of PAHs in Shanghai showed regional distribution, industrial zone>urban zone> suburban zone. There were obivous regional differences, and the mean deposition fluxes of SDK was 7.54 times than DSH. This had a great relationship with the location of each region.Compared with deposition fluxes abroad, atmospheric deposition fluxes of PAHs was significantly higher than foreign developed cities, higher than some areas of Germany by two orders of magnitude, lower than our northern cities, but higher than the southern cities.To quantitatively diagnose the potential source of PAHs in atmospheric deposition, PMF and FA-NNC models were used, both models had exactly the same source apportion results. According to the PMF, proportion of four kinds of PAHs source in spring were respectively, vehicle emissions of 42.53%, coal combustion of 18.84%, volatile oil leakage of 27.15%, coking and coal smelting of 11.48%. Vehicle emissions, coal combustion, volatile oil leakage, coking and coal smelting respectively contributed to 36.29%,19.67%,22.45%,18.32% in summer. The ratios were 39.55%,19.67%,22.45%,18.32% respectively in autumn. The proportion of each emissions in winter was 34.27%,30.89%,14.05%,20.79%. According to output of FA-NNC model, in spring, vehicle emissions,42.01%, coal combustion,16.24%,volatile oil leakage,27.39%, coking and coal smelting,13.36%. The ratio in summer was 39.41%,13.01%,28.71%,18.87%, respectively. In autumn, the contribution of apportionment source was 38.14%,13.01%,28.71%, 18.87%, respectively. In winter, vehicle emissions,36.82%, coal combustion, 31.08%,volatile oil leakage,16.79%, coking and coal smelting,15.10%, respectivelyTo assessment the ecological risk of eight samples, we used RQ-TEQ complex model. According to our researches, there were 83.33% of month in serious pollution throughout the year, WJ, WJC, WGQ,NQ had 50%,50%,75%,33.3%, respectively. The pollution index p of DSH was between 1 and 2 and DSH was in polite pollution. In a conclusion, the atmospheric deposition in Shanghai was much serious.The Spearman correlation cofficient was adopted to discover the relevance of PM2.5 and meteorological parameters. It was found a significant negative correlation between PM2.5 and visibility in spring, autumn and winter. However, it’s not the case in summer. The correlation between PM2.5 and wind speed was complex, it was related significantly in spring(R2=-0.464, p<0.01), in summer (R2= -0.370, p< 0.01). Due to the influence of northern contaminated air, the correlation is not obvious in autumn and winter. The relationship between PAHs and related meteorological parameters was also analysed, correlation between daily temperature and E 16PAHs had poor cofficient in spring, summer and spring. In winter, the relationship between temperature and E 16PAHs was strong (R2=-0.377, p< 0.05). Relative humidity and E 16PAHs showed a obvious negative correlation in spring, autumn and winter, but summer was not obvious. Visbility and E 16PAHs were not correlated. Wind speed and E 16PAHs showed significant correlation in the spring and summer, however, it was not the case in the autumn and winter.ILCRs model assess the cancer risk of ingestion, dermal contact and inhalation. The risk of ingestion and dermal contact exposure was higher among three exposure way, while, inhalation is lower. The cancer risk showed that winter> autumn> spring> summer throughout the year, the total cancer risk of exposure was within the acceptable range. Based on the differences between the various groups, the ingestion risk was higher than adults, the exposure of adult was higher than children in dermal contact exposure. The risk of inhalation was much small, adult were higher than children, but not obvious differences.We used HYSPLIT model to simulate the backward trajetories of PM2.5. The sampling site was affected by the north and south stream in spring and autumn. Summer mainly affected by east coastal aristream was the least polluted. Winter by cold air south of contaminative air mass was much more serious. From the spatial distribution and concentration of polluted airflow trajectories, PM2.5 was mainly influenced by short-distance migration stream, the impact of long-rang transport was relatively small, meanwhile, the airflow near the ground had greater impact. At last, The PSCF and DWT methods were used to analysed the potential source area of PM2.5. It was mainly came from Henan, Jiangsu and Anhui in spring. PM2.5 pollution was light in summer. Affected by north airstream, potential pollution sources were chiefly concentrated on the roadline of northern cold air, while, it was also affected by the south air mass. Winter air pollution was extremely serious, what’s more, Inner Mongolia plateau, north China, Henan and Jiangsu is PM2.5 potential contribution centralized sources. |
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