Source And Spatial Characteristics Of Black Carbon And Its Correlation With Pahs In Surface Soil Of Shanghai

Urban surface soil plays an important "source and sink" role in the process of Black Carbon(BC)environment.As the urbanization process continues to advance,BC continues to accumulate in the surface soil,which has a profound impact on human health and the global carbon cycle process,the problem of urban surface soil safety needs urgent attention.At present,the domestic and foreign attention to BC in surface soil is mainly concentrated in BC precursors.The BC components Char and Soot are not well understood in the surface soil,and different BC components have persistent organic matter.Pollutants,especially Polycyclic Aromatic Hydrocarbons(PAHs),have different fate and conversion effects.In-depth study of the occurrence characteristics of Char and Soot in the surface soil and their correlation with PAHs will help to understand BC Environmental behavior.At the same time,quantitatively revealing the driving factors behind the spatial characteristics of BC helps to adopt a more scientific and effective method to control and control urban soil,and also provides a theoretical basis for urban soil management.In this study,the surface soil of Shanghai was collected on a 5 km × 5 km grid.The sample height covered different point sources,traffic loops and different functional areas in Shanghai.the study.Based on GIS geostatistical analysis,combined with the spatial hotspot detection model,the degree of spatial agglomeration of BC in surface soil was explored.Using the Spearman correlation coefficient,the correlation between PAHs and BC,Char and Soot content was analyzed to explain the adsorption behavior of BC to PAHs.Based on this,PAHs feature ratio method is used to analyze the source of BC.Introduce the Geographical Detector model to quantitatively reveal the driving factors and explanatory power differences of the BC spatial characteristics of Shanghai's surface soil,and explore the interaction effects of different driving factors on the BC spatial differentiation of Shanghai's surface soil,with a view to the Shanghai soil Quality and safety provide scientific governance measures.The innovative results and practical significance of this research are as follows:(1)The range of BC content in surface soil samples in Shanghai ranges from0.26 to 41.06 mg/g,with an average value of 4.47 mg/g.The content of Char ranges from 0.01 to 39.67 mg/g,with an average value of 2.64 mg/g,accounting for 58.93%of the average BC content.The content of Soot ranges from 0.01~13.74 mg/g,with an average content of 2.42 mg/g.The content of 16 PAHs controlled by the US Environmental Protection Agency ranges from 72.01~4765.56 ng/g,with an average content of 589.22 ng/g.Compared with the domestic and foreign research results,the surface soil BC and PAHs in Shanghai are at a moderate pollution level.(2)The content of BC is on the 4th Ring Road in Shanghai,mainly divided between north and south,showing an increasing trend from the suburban ring to the inner ring.In different functional areas,the overall variation characteristics of BC content are: traffic roads> industrial areas> commercial areas> residential areas>cultural and educational areas> agricultural areas> park green spaces.The BC content presents the distribution characteristics of high in the north and low in the various districts and counties.The highest area is Baoshan District,followed by the central urban area,Jiading District,Minhang District,Pudong New District and Baoshan District.From the point of view of the composition of different ring numbers,high concentration PAHs are mainly concentrated in rings 5 and 6,with contents of1297.74 ng/g and 1297.74 ng/g,respectively,accounting for 84.68% of the total PAHs content.From the perspective of PAHs monomer components,the highest BaA and Chr contents are 95.32 ng/g and 96.85 ng/g,respectively.From the perspective of different traffic ring roads,the spatial characteristics of surface soil PAHs in Shanghai are as follows: Central Ring> Outer Ring> Suburb Ring> Inner Ring> Outer Ring.The spatial characteristics of content showed the same trend.(3)GIS-based analysis of BC space hotspots shows that the BC global spatial autocorrelation(Moran I)index is 0.43,and BC is significantly positively correlated in different grid areas,indicating that Shanghai BC pollution is concentrated and continuous,with high and low values of north and south The spatial differentiation characteristics are obvious,and the mutual influence between regions is obvious.There are a total of 5 BC hotspot gathering areas in the study area,three of which are high-value gathering areas: northwest of Shanghai,central urban area,and southernChongming.The gathering areas are oval.The contaminated areas are concentrated and contiguous,affecting a large area and causing serious pollution.,Generally distributed in the north-south direction.Two are low-value areas: southwestern Shanghai,eastern Chongming and eastern Shanghai.The low values in southwestern Shanghai are nearly circular,and the correlation in the direction is not obvious.(4)The Spearman correlation coefficient analysis showed that the correlation between BC and HMW PAHs in the study area was the most significant(r = 0.253,p<0.05),and Soot had the most significant positive correlation with LMW PAHs and MMW PAHs(p <0.05)The sex r is 0.249 and 0.221 respectively,while the correlation between Char and HMW PAHs(r = 0.201,p <0.05)is more significant.The good correlation between PAHs and BC and TOC shows that BC and TOC in Shanghai's surface soil play an important role in PAHs enrichment and spatial distribution.(5)Based on PAHs characteristic marker ratio method and BC / OC,Char / Soot ratio,the source analysis of BC is carried out.The results show that the soil BC / OC ratio in the study area is 0.84,indicating that BC is a fossil fuel combustion source.The Char / Soot ratio result was 2.07,indicating that the main source of BC was coal combustion emissions.PAHs characteristic marker ratio method,the results show that the Flu /(Flu + Pyr)ratio range is 0.32~0.60,the average value is Inp /(Inp + BghiP)ratio range is 0.17~0.59,and the average value is 0.56,indicating that the Shanghai surface soil The sources are mainly biomass/coal combustion sources and mixed sources of incomplete combustion of petroleum.(6)Geographical Detector is used to detect the driving factor of BC spatial characteristics.The result of the factor detector shows that the population density q value is at most 0.936,which is the dominant factor of BC spatial heterogeneity.The human factor has the largest explanatory power.Spatial heterogeneity has a relatively important position,and meteorological factors have the weakest explanation for BC spatial heterogeneity.The detection results of the interactive detector show that each driving factor mainly exhibits three interaction relationships of non-linear enhancement,dual-factor enhancement and single-factor nonlinear attenuation.Any combination of factors can enhance or weaken the single factor's characteristics of BCspatial differentiation.Explanatory power.In summary,this thesis has improved the research on the surface soil BC and the components Char and Soot in Shanghai,and deeply explored the adsorption behavior of Char and Soot for PAHs.At the same time,it quantitatively revealed the spatial heterogeneity of BC Drive factors and differences in explanatory power,pointing out that Shanghai 's surface soil BC pollution control should focus on improving the energy structure and controlling the emission of vehicle pollutants in key areas,timely attention to changes in driving factors such as meteorological conditions and socioeconomics,and enhanced monitoring from multiple indicators manage soil safety.