| The ecological and environmental problems brought about by the rapid urbanization process continue to threaten the health of human beings and the sustainable development of society.As a kind of environmental media that collects a lot of pollution in the city,its pollution problem has been widely concerned by scholars.As a kind of organic pollutant with teratogenic,carcinogenic and mutagenic effects,PAHs are typical pollutants in urban soils.In the past,the spatial distribution of PAHs in urban soils was usually studied by simple spatial interpolation.The dynamic accumulation,migration and transformation processes of PAHs use a large-scale fugacity model to simply simulate the distribution of pollutants in various media.The study of soil exposure risk only stays at the risk assessment level.How to control risks still lacks effective technologies and methods.Shenzhen is a great sample of research on rapid urbanization in China over the past 40 years.The research on PAHs pollution in urban soil of Shenzhen is typical.This paper intends to obtain the spatial distribution characteristics of the content,composition and source of PAHs in urban soils of Shenzhen by using 93 soil samples of urban soils from different land use modes in the main urban area of Shenzhen.Complete high spatial resolution mapping,explore the quantitative relationship between soil PAHs pollution and various influencing factors.The urban environment multi-media fugacity model was used to simulate the migration and accumulation process of PAHs.Combining the multiple linear regression model with the source analysis of pollution,the green space pattern optimization parameters and emission reduction parameters are applied to the fugacity model,and the multi-scenario optimization strategy of green space pattern optimization and pollution source reduction space joint optimization is proposed.Corresponding planning and countermeasures are proposed for the prevention and control of PAHs pollution risks.The main conclusions obtained are as follows:(1)The pollution of PAHs in the urban soil of Shenzhen is lighter with the stronger spatial heterogeneity.∑PAHs ranged from 73 to 2310 ng/g with an average of 494 ng/g.The main pollutants were phenanthrene,fluoranthene,anthracene,quinone,benzo(b)fluoranthene,∑PAHscarc was between 24 and 1275 ng/g,with an average of 257 ng/g,and carcinogenic PAHs accounted for 55.2%of the total.The detection rate of each PAHs reached almost 100%.(2)The distribution of PAHs is affected by multiple factors,and combined with the influence of various factors and residuals,a spatial refined mapping model is proposed.According to the influence weights,the factors are green space distance,SHDI,road density,PH,NDVI,grain size and organic carbon content.The regression model fitting equation R2=0.411.Compared with the simple spatial interpolation method,the spatial fine-grained cartographic model has better fitting goodness,higher precision and more realistic reflection of the spatial distribution of PAHs pollution.(3)The source of PAHs emissions is mainly based on traffic,and the health risks are controllable.Taking BaP as an example,the emission inventory was constructed.The BaP emission density in the study area was between 0 and 12.81 Kg/Km2,with an average of 0.76 Kg/Km2.Among them,the contribution rate of trafic emissions to total BaP emissions exceeds 95%,and urban living emissions and corporate and factory emissions also contribute to certain BaP pollution.Through the comparison of the ratio method and the positive definite factor method,the main sources of PAHs in the urban area of the study area are automobile exhaust,coal combustion and industrial fuel combustion,and the contribution rates reached 51%,23%and 15%respectively.The average health risk of PAHs in children and adults in the study area were less than 10-6 within acceptable limits.However,the maximum health risk for children and adults exceeds 10-6,and there is a potential health risk.(4)In the simulation results of the urban environment multi-media fugacity model,the spatial distribution of BaP content in most media is highly correlated with the spatial pattern of the emission inventory,while the soil medium exhibits certain specificity,which is related to the area of various land use types.The simulated value of BaP content in the soil medium is larger than the measured value(the simulated maximum value is 260.2%of the measured maximum value),but the average value is small(the simulated average is 34.7%of the measured average).(5)Different optimization scenarios are effective in controlling the risk of PAHs pollution in urban soils.The effect of the pollution source emission reduction scenario is obvious,and the effect of regulating the maximum value is better than that of the average value,the spatial distribution is not obvious.The green space pattern optimization scenario can significantly reduce the extreme value of urban PAHs pollution,but the effect on the average is weaker than the pollution source reduction scenario.Compared with the separately optimized scenarios,the joint optimization has better effect on both extreme value and the average value,and the spatial distribution is more balanced.It can not only improve the overall pollution situation under the pollution source emission reduction scenario,but also realize the green space pattern optimization to reconstruct the spatial pattern of pollution.Under the scenario ensures the health risks to the health are minimized. |
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