Emission Characteristics And Emission Factors Of Motor Vehicles Based On The Test In A Road Tunnel

With the rapid development of urbanization and the continuous improvement of vehicle ownership in China,on-road traffic emission has become one of the important sources of urban air pollutants.The vehicle pollutant emission test was carried out on 15-20 March 2016in Qinling highway tunnel.The spatial and temporal distributions of gaseous pollutants and particle concentration in tunnel were analyzed,the concentration spectrum and size distribution characteristics of particle emitted by vehicles were studied.The average pollutants emission factors were calculated combined with the tunnel traffic and meteorological parameters during the test.And the comprehensive emission factors of pollutants from gasoline vehicle and diesel vehicle were obtained by the least square method.The main conclusions of this paper are as follows:?1?The average traffic volume?M±D?in the XH?2.58%uphill grade?and HX?-2.58%downhill grade?tunnel were 374±246 and 330±199 veh/h respectively,and the diesel vehicle accounted for 45.33%and 55.58%during the testing period respectively.The concentration of gaseous pollutants from vehicle exhausts increases with the increase of engine load when vehicle climbs.The NOx,CO and SO₂ concentration of fixed reference site in XH tunnel are1129.15±563.68,1941.38±1201.17 and 32.96±113.68?g/m³ respectively,which are 4.04,1.04 and 1.5 times higher than those at the HX tunnel,respectively.The NOx concentration in the tunnel is mainly contributed by NO from vehicle emission,and the NO/NOx is about 0.9at moved site.The concentration gradient of NO,SO₂,CO and O₃ in the tunnel are all nonlinear,and the concentration distributions of those pollutants at the moved site are more dispersed than those at the fixed reference site.The accumulation efficiency of the gaseous pollutants concentration satisfies the change regulation of CO<O₃<SO₂.?2?The concentration gradient of the PM_2.5.5 number in the tunnel is nonlinear,and the concentration distributions of PM_2.5.5 inside the tunnel are more dispersed than those at tunnel entrance.The vehicle engine load increases and the higher concentration of particulate matter are emitted when the vehicle climbs.The number,surface area and mass concentration of PM₁₀0 at fixed reference in XH tunnel are?4.77±3.37?×10⁵#/cm³,?5.41±3.46?×10³?m²/cm³and 0.96±0.78 mg/m³ respectively,which are 2.77,2.97 and 3.69 times higher than those at the corresponds measured sites in HX tunnel.The particle size distribution of vehicle emission was analyzed by logarithmic normal fitting.The particles in the diameter range of6.83-14.06 nm are mainly for the nucleation of the gaseous pollutants emitted from motor vehicles;the particles emitted by gasoline and diesel vehicle are range of 18.75-28.91 nm and88.92-92.90 nm,respectively.?3?The vehicle engine condition has a greater impact on vehicle emission,and the concentrations of pollutants emitted by diesel vehicles are significantly higher than those of gasoline vehicles.The PM_2.5.5 number and mass concentration,NOx,CO,VOCs and SO₂emission factors of the motor vehicles in XH tunnel are?1.72±1.07?×10¹⁴#/?km·veh?and0.72±0.52,5.55±2.28,2.39±1.31,0.90±0.73,1.88±0.98 g/?km·veh?,respectively.And emission factors of diesel vehicles are?2.42±0.25?×10¹⁴#/?km·veh?and 1.21±0.12,10.24±0.64,4.30±0.37,1.02±0.1,3.42±0.27 g/?km·veh?,which are 0.92,1.53,4.08,11.95,2.57,and 37.6 times higher than those of gasoline vehicle emission factors.Compared with domestic and foreign research,the vehicle emission factors are decreasing as a whole with the improvement of vehicle fuel quality,engine efficiency,exhaust post-treatment technology and emission standards.