Study On The Three-dimensional Spatial Distribution Characteristics And Health Risk Assessment Of Volatile Organic Compounds In Typical Industrial Parks

As the important precursors for the formation of ozone and secondary organic aerosol（SOA）,volatile organic compounds（VOCs）participate in the complex atmospheric chemical reactions,and cause harm to human health.Industrial emission is an important anthropogenic source of VOCs as a key area of industrial emissions.Therefore,identifying the emission characteristics of VOCs in industrial parks is a basic prerequisite condition for reducing industrial VOCs emissions.At present,most studies mainly focus on the emission characteristics of VOCs on the ground level in industrial parks,meanwhile,less attention was paid to the high-altitude evolution process and characteristics of VOCs in industrial parks.Therefore,it is necessary to carry out the three-dimensional space investigation of VOCs in industrial parks from the ground and different heights.This means will not only identify the characteristic pollutants of VOCs emitted by industrial parks,but also help to strengthen the understanding of the vertical diffusion process of VOCs in industrial parks,and provide an important scientific basis for the prevention and control of VOCs in industrial parks.In this thesis,two typical industrial parks in South China were selected as the research areas.Three-dimensional observations of VOCs were carried out in the horizontal direction of the ground and the vertical direction of the high altitude,respectively.Multiple sampling points were set on the ground according to the characteristics of the industrial park.In the vertical direction of the high altitude,a multi-component monitoring system for air pollutants carried by unmanned aerial vehicles（UAVs）developed by our team is used to collect VOCs samples in an innovative way by UAVs carrying sensors and suma canister.The collected samples were analyzed by preconcentration-GC-MS.The technology is finally applied to observation in two typical industrial parks.Furthermore,we systematically analyzed the concentration level,composition,distribution characteristics and dominant species of VOCs on the ground and at high altitudes,discussed the contribution of VOCs to ozone formation,and evaluated the health risks of VOCs at different heights.The main results were as follows:（1）The average concentration of TVOC（41±24 ppb）on the ground is pretty high in an industrial park,Guangzhou.Alkanes were the largest contributor（35%）,followed by aromatic hydrocarbons（24%）.Undecane（27%）and isopentane（23%）are the main substances in alkanes;toluene（32%）and m/p-xylene（32%）are the dominant species of aromatic hydrocarbons.By studying the spatial distribution of VOCs on the ground of industrial parks,it is found that the composition of VOCs is greatly affected by the nearby emission sources,the possible sources of VOCs are found to be automobile exhaust,industrial solvent evaporation,printing,pharmaceutical manufacturing and other industries.TVOC concentrations in the upper air are lower than those on the ground,decreasing from the ground（42±13 ppb）to 50 m（30±10 ppb）.Alkanes occupy the largest proportion（23%-37%）at high altitude,and its dominant species is n-hexane,followed by aromatic hydrocarbons（20%-39%）with toluene as its dominant species.Besides,the concentration levels of toluene increased with altitude.（2）The influence of VOCs for O₃ generation was understood by analyzing the relationship among VOCs,NO_X and O₃.The ratio of VOCs to NO_X in the industrial park was between 0.5 and 5.7,indicating that the industrial park was a VOCs-limited region.Alkenes and aromatic hydrocarbons mainly from motor vehicles and industrial sources are considered to be the main potential contributors to the formation of O₃ in industrial parks.In addition,it was found that NOx in VOCs sensitive area would undergo titration reaction（NO react with O₃ to generate NO₂ considering as the titration reaction）to consume O₃ that affecting the formation of O₃.Therefore,the O₃ emission reduction policy in the study area should consider controlling VOC emissions and NOx titration.Besides,the ozone formation potential（OFP）and OH loss rate(L_OH)of high-altitude VOC were estimated.Olefin contributed most,followed by aromatic hydrocarbons,and n-hexene was the most critical active species of atmospheric VOCs in the industrial park.Trichloroethylene and chlorobenzene need to be emphasized due to their certain non-cancer and cancer risks from the assessment for the health risk of VOC.（3）The overall concentration level of the ground（31±33 ppb）in an industrial park of Shantou is quite high,while at the upstream of the concentration level studied before in the Pearl River Delta.The contribution of alkanes（39%-66%）to the ground is prominent.n-Hexane（70%-81%）and isopentane（5%-12%）mainly from motor vehicle exhaust are found to be the dominant species of the ground.The concentration of VOCs in the upper air is 49±5-88±13 ppb higher than that in the ground,and the contribution of aromatic hydrocarbons is prominent in the upper air.The concentration of aromatic hydrocarbons increased significantly in the 5-10 m,indicating that factory operation emissions have a great impact on the 5-10 m.Toluene,ethylbenzene,m/p-xylene,styrene and o-xylene are the main contributors to high altitude aromatic hydrocarbons.Cluster analysis showed that toluene,styrene and ethylbenzene,m/p-xylene,o-xylene belonged to different sources.Compared the ratio of m/p-xylene to o-xylene and ethylbenzene to toluene,it was found that industrial emissions had a great influence on the vertical distribution of VOCs.The ratio of m/p-xylene to ethylbenzene indicates that the air mass might be fresh at 5-10 m which was affected greatly by the local industrial emissions.（4）Preliminary analysis of the correlation between NO_X,VOC and O₃ shows that the correlation between NO_X and O₃ is stronger than that between VOC and O₃,indicating that the formation of O₃ may be mainly affected by NO_X.The ozone formation potential at high altitude is higher than that on the ground.Alkenes on the ground contribute the most to OFP.Aromatic hydrocarbons（AHs）contribute the most to OFP at high altitude.o-Xylene contributes the most to OFP among AHs,at the same time,it is also the most critical active species of VOCs in Shantou Industrial Park.To assess the health risks of VOCs at different heights,it was found that chlorobenzene had high non-cancer and cancer risks for human health in Shantou Industrial Park;o-xylene showed high non-cancer risk at high altitude,while ethylbenzene showed high cancer risk at high altitude,which should be paid attention to.In summary,this thesis mainly analyzed the concentration composition and distribution characteristics of VOCs in the three-dimensional space of typical industrial parks,observed the changes of VOCs in the high altitude which near surface,discussed the relationship between VOCs and O₃ formation,understood the reaction activity of VOCs in the high altitude,and evaluated the health risk of VOCs in industrial parks.This study provides an important reference to the investigation of the vertical distribution of VOCs,and a reliable data basis for the scientific development of pollution prevention and control measures.