| Increased level of atmospheric aerosol can severely impact atmosphere visibility, publichealth and climate. With the rapid increase of vehicles in China, particulate emission has beenbecome one of the most important pollutant sources for atmospheric aerosol. Acomprehensive knowledge on physicochemical characteristics of vehicle particulate emissionis required to understand particle formation mechanism, hazards to the atmosphereenvironment, source assignment and ways to reduce particulate emission from motor vehicles.In this dissertation work, detailed physicochemical characteristics of particulate emissionwere investigated by dynamometry and roadside sampling. For the roadside experiment, anew method was proposed to calculate the vehicle emission factor with different engine types.This thesis is composed of the following parts:(1) In the dynamometer experiment, ultra low sulfur diesel fuel (ULSD, sulfur contentless than10ppm), biodiesel (BD) and low sulfur diesel fuel (LSD, sulfur content lessthan400ppm) were used as the fuels. Detailed physicochemical characteristicsincluding size-dependent particle volatility, particle morphology, nanostructure,oxidation property and major composition were investigated. The size-dependentvolatility was investigated on the basis of number and mass measurements. It wasfound that, the use of biodiesel could reduce the brake specific emission of volatilesubstance effectively in comparison with LSD. While volatile substances in thebiodiesel particulate are notably greater than ULSD particulates and moreconcentrated in the particulates with small size. (2) Particle morphology, nanostructure and oxidation property were also investigated overranges of engine operation conditions, aerodynamic sizes, and fuel types. Theoxidation experiments suggest that the oxidation property of diesel particulate dependon the primary particle size, volatile fraction, and nanostructure. Due to the smallerprimary particle size, larger volatile content and greater disordered inner nanostructure,biodiesel particulate exhibite stronger tendenty to oxidation than those from ULSDand LSD. Moreover, in-cylinder combustion parameter and fuel properties control theprimary particle size, volatile content and inner nanostructure of diesel particles.(3) Analysis of particle composition included organic carbon, element carbon andpolycyclic aromatic hydrocarbons. In this thesis, the effect of engine load,aerodynamic size and fuel type on particle composition were investigated. The use ofbiodiesel appears to reduce particulate emissions from diesel combustion. Thissuppression effect is exhibited mostly in the reduction of elemental carbon and largermolecular weight PAHs. Moreover, the particle compositions were found to be loadand size dependeent.(4) Roadside sampling was made immediately adjacent to a freeway in Shanghai. Particlesamples were collected during daytime and nighttime. The physicochemicalcharacteristics of particle samples were investigated including size-resolved particlemass concentration, morphology, composition. These results were compared withthose of background samples. The results indicated that the vehicle emissionscontributes mostly to the size range less than400nm, and the mass concentration ofelement carbon, nitrate and PAHs in the particles exhibits the most notable increase,when compared to the background. The source assignment method of positive matrixfactor was used to analyze the contribution ratio of different emission sources and theresults were used for the calculation of vehicle emission factor of different enginetypes. The results indicate that particle emission from diesel motor vehicles is themajor contributor of roadside particulate, especially for ultrafine particles with thecontribution ration above60%. In Shanghai, the emission factor of in-use diesel motorvehicles is still in a higher level in the comparison with some developed countries andregions. |
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