Characteristics Of Ozone Precursors Emitted By Motor Vehicles And Ozone And Secondary Organic Aerosol Formation Potential In Guanzhong Region,China

In recent years,ambient air quality monitoring data show that O₃ has become a secondary air pollutant that affects the air quality of Guanzhong urban agglomerations after PM_2.5,and has received widespread attention.In this paper,atmospheric observation points are set up in five cities in the Guanzhong plain,and typical urban tunnel and road were selected as sampling points to obtain observation data of atmospheric background and vehicle emission of O₃ and its precursors（NO_x and VOCs）in Guanzhong area.Analyzed the influence of atmospheric background and traffic environment O₃ and NO_x concentration characteristics and the VOCs（alkanes,alkenes,alkynes,aromatic hydrocarbons,halogenated hydrocarbons and OVOC,etc.）on O₃ formation.The maximum incremental reactivity（MIR）coefficient method and fractional aerosol coefficients（FAC）method were used to estimate the O₃ and SOA formation potential of different VOCs components in the atmospheric,road,and tunnel environments in the Guanzhong region,and then obtained the VOCs components with the greatest potential for O₃ and SOA formation from motor vehicles in the Guanzhong basin.The results showed that:（1）The TVOC concentrations in the atmosphere,road,and tunnel were 68.66ppbv,66.29ppbv,and 86.73ppbv,respectively,and the TVOC concentrations in the tunnel were the highest,which were 1.31 and 1.26 times the road and atmospheric,respectively.The concentration of alkanes in the atmosphere was accounting for 30.8%～41.5%of TVOC,the aromatic concentration of road was 21.43ppbv（32.3%）,and the concentration of alkanes in tunnel was 45.12ppbv（52.0%）.Acetylene,ethane,and ethylene were the three highest concentrations of VOCs in the atmosphere in Guanzhong.Formaldehyde,ethylene,and trans-2-butene are the three highest concentrations of VOCs in the road.Isopentane,ethane,and n-butane were the three highest concentrations of VOCs in the tunnel.（2）The TOFP of atmospheric VOCs in the autumn and winter were 197.65ppbv and156.55ppbv,respectively.The activity of alkene to generate O₃ was the largest,accounting for40.1%to 56.1%of TOFP.Road TOFP was 313.15ppbv,OVOC（38.8%）contributes the most to TOFP,and formaldehyde（108.61ppbv（34.7%））was the highest VOCs component of OFP.The TOFP in the tunnel is 247.39ppbv.The largest contributor to TOFP was alkene,accounting for 57.1%of TOFP.Acetylene was the VOCs component with the largest difference between the transportation environment and the OFP in the atmosphere.OFP acetylene was less than1ppbv in traffic environment,accounting for less than 0.4%,while OFP acetylene in the atmosphere was 87.8ppbv,accounting for 4.0%.（3）The TSOAFP of atmospheric VOCs in autumn and winter were 2.79μg/m³ and 0.75μg/m³,respectively.The activity of aromatics to generate SOA was the highest,accounting for96.4%to 97.4%of TSOAFP.The contribution of alkanes and alkenes to atmospheric SOA formation was less than 4%.Road TSOAFP was 3.68μg/m³,aromatic hydrocarbons contribute85.0%to SOA formation,followed by alkanes（14.8%）;tunnel TSOAFP was 2.62μg/m³,and aromatic hydrocarbons contribute 92.2%to SOA.In the atmosphere,road and tunnel environment,the VOCs components with high SOA activity were aromatic hydrocarbons（especially benzene series）.（4）The average T/B（toluene/benzene）of autumn and winter atmospheres in Guanzhong area were 2.96 and 1.55,and the T/B values of road and tunnel were 2.40 and 1.08,respectively.The X/E（m/p-xylene/ethylbenzene）value of the atmosphere in autumn and winter was between1.56 and 2.08,the X/E value measured on the road was 1.00,and the X/E value measured on the tunnel was 0.05.In the tunnel,the correlation between isopentane and BTEX（r）was between 0.795 and 1.000,which was highly correlated,while in the road,the correlation between isopentane and benzene was the largest（r=0.816）,and the correlation with toluene low（r=0.044）,negatively correlated with xylene and m/p-xylene.In the atmosphere of Guanzhong region,the r of isopentane and benzene was between 0.06 and 0.55 in autumn,the r of isopentane and toluene was between 0.40 and 0.60,and the r of isopentane and benzene was between 0.04 and 0.82 in winter.The r of alkane and toluene was between 0.17 and 0.87.The research results can provide a reference for the formulation of countermeasures for controlling vehicle emissions,reducing O₃ and SOA precursor concentrations,and suppressing summer O₃ and winter SOA generation in the Guanzhong urban agglomeration.It is conducive to improving the air quality,providing scientific guidance for comprehensive control of atmospheric composite pollution,and achieving coordinated control of regional O₃ and particulate matter.In addition,it is of great significance to formulate emission standards for different types of vehicles,improve oil products,improve vehicle exhaust control,and improve motor vehicle exhaust aftertreatment devices.