Study On Source Appointment And Health Risk Assessment Of Roadside Black Carbon In Xi’an

Black carbon（BC）is one of the important indicators of atmospheric particulate matter exposure assessment,but it is rarely reported in the road environment,which is a hot spot of pollution exposure.As a result,the temporal and spatial distribution of road environment BC is still unclear.In order to clarify the pollution characteristics and health effects of BC in the road environment,it is necessary to carry out high-temporal-resolution monitoring research on BC in the road environment to provide a theoretical basis for road BC emission reduction prevention and control.In this study,based on the field data of BC at typical roadside station in Xi’an,the Aethalometer model was used to analyze the contribution of traffic sources to BC in the road environment.The time distribution characteristics of total BC and different sources of BC,and the internal relationship between traffic source BC and traffic conditions,background concentration,meteorological parameters were studied,and the passive cigarette equivalent model was used to quantitatively evaluate the health risks of BC to the public in the road environment.The main results of this research are as follows:Firstly,the monitoring results of BC concentration showed that:（1）The average concentration of BC on the roadside is（3035.66±1299.39）ng/m³,which is about 1.22 times that of the background station,highlighting the relatively high BC exposure risk of the road environment.（2）BC concentration on working days was significantly higher than that on weekends.The former is about 1.7-2.4 times that of the latter.（3）In general,the BC concentration at the roadside station showed the characteristics of three peak daily changes in the morning,middle and evening,with the highest peak in the morning or noon.Secondly,the analysis of roadside BC sources showed that:（1）The fossil fuel source BC(BC_ff)dominate the contribution to BC,with an average contribution of more than 80%both in the background environment and roadside environment,indicating the significant contribution of vehicle emissions.In addition to traffic sources,the contribution of biomass combustion source BC(BC_bb)to the BC concentration of the road environment cannot be ignored.（2）There is a significant positive correlation between the total motor vehicle traffic,the number of gasoline vehicles,compressed natural gas buses and BC_ffconcentration.In addition,the slow idling of vehicles in road congestion corresponds to a higher traffic source BC contribution.（3）Due to changes in the contribution of traffic source emissions and pollutants dispersion condition,the correlation between BC_ff concentration and meteorological factors has temporal heterogeneity,but overall,the concentration of BC and BC_ff have significant negative correlation with temperature and significant positive correlation with relative humidity,wind speed,and background concentration.Finally,the passive cigarette equivalent model was used to evaluate the health risk of roadside BC.The results showed that:（1）The arithmetic average estimated value of the health risk（expressed in equivalent passive cigarette）caused by BC on the roadside is up to 21,which is about 16,45.6,15.2,and 7.2 corresponding to low birth weight and decreased lung function in school-age children,cardiovascular death and lung cancer,respectively.（2）Affected by traffic volume and the distribution of other BC emission sources,the difference in BC concentration on both sides of the road and between different sections would bring certain health risk losses or gains.