| In this study,sampling campaign was conducted at the North Street,the 3rd West Ringroad and the Hongguang Park at Xi’an.Among of which,the North Street and the 3rd West Ringroad were typical urban main roads,and the Hongguang Park was the reference point.The annual and diurnal variations in concentrations of PM2.5,O3,NOx,CO and THC were analyzed in the roadside environment.Samplings of VOCs were conducted by the Summa canister sampling method.MIR and FAC coefficient method were applied to estimate the OFP and SOAFP of VOCs.The key VOCs in terms of O3 and SOA formation were identified.Results showed that:（1）There were seasonal variations in concentrations of O3,PM2.5,NOx and THC at the roadside environment.Atmospheric O3 concentration was high in summer and low in winter.In summer time,O3 concentrations in the North Street and 3rd West Ringroad were 68.80±16.85and 38.11±9.41μg/m3,respectively.The variation trends of PM2.5,NOx and THC were inverse to that of O3.（2）The hourly traffic volumes of the North Street and the 3rd West Ringroad were 4187and 2502 vehicles per hour,respectively.Diesel vehicles accounted for 0.8%and 7.2%of the total traffic volume in the North Street and the 3rd West Ringroad,respectively.The hourly concentrations of PM2.5 and NOx in the North Street were lower than those in the 3rd West Ringroad,mainly due to the differences in traffic volume and proportions of diesel vehicles.（3）The average concentrations of TVOC in the North Street and the 3rd West Ringroad sections were 113.85 and 111.42 ppbv,respectively.The TVOC concentrations under the both of the road sections were higher than that of the reference point（21.79 ppbv）.The total concentrations of OVOC and alkanes were 71.18 ppbv in the North Street and 69.26 ppbv in the 3rd West Ringroad,accounting for over 60%of the TVOC concentrations.Considering OVOC,ethylacetate and propanal at roadside sections accounted for 60.2%and 38.1%of OVOC concentrations,respectively.Among the measured alkanes,the concentration of ethane was 9.17 ppbv in the North Street,the concentration of isopentane was 12.06 ppbv in the 3rdWest Ringroad.The concentration of isopentane in roadside sections was 9.36 ppbv higher than the reference point.（4）The total ozone formation potentials（TOFP）in the North Street,the 3rd West Ringroad and reference point were 263.10,289.48 and 234.76 ppbv,respectively.Among the aromatic in the North Street and the 3rd West Ringroad,the OFP of p/m-Xylene were 20.52 and15.62 ppbv,respectively,accounting for about 20%of the OFP of aromatic.In the OFP of OVOC in sections,the OFP of acetaldehyde（the North Street）and propanal(the 3rd West Ringroad)contributed to the TOFP 9.2%and 11.3%,respectively.Comparing the reference point,the OFP of propanal and isopentane at the roadside sections were 22.75 and 13.60 ppbv higher than that of the reference point,respectively.（5）The total secondary aerosol formation potentials（TSOAFP）in the North Street and the3rd West Ringroad sections were 5.11 and 4.18μg/m3,respectively.The potentials for SOA formation of aromatic were 4.86 and 3.82μg/m3,which accounted for 95.2%and 91.3%of TSOAFP,respectively.Toluene was one of the key species in the formation of SOA,accounting for 28.4%and 23.3%of the total aromatic formed SOA,respectively. |
