Study On The Characteristics Of Volatile Organic Compounds And Particulate Matter From On-use Vehicles In Wuhan

The motor vehicles contribute more and more air pollution into the urban areas in China with the rapid growth of vehicles In this paper,11 typical vehicles selected in Wuhan were tested base on a combined portable emission measurement system（PEMS）,the volatile organic compounds（VOCs）from the vehicle’s exhaust were sampled by the Teflon sampling bags and the particulate matter（PM）were sampled by the filter membranes.The emission characteristics of volatile organic compounds and particulate matter were studied by analyzing those samples in labs.The main conclusion of this paper are as follows:1.The concentration of VOCs obtained by GC-MS analysis showed that the average emission concentrations of total VOCs（TVOCs）from gasoline and diesel vehicles in Wuhan were 5.885±2.365 mg/m³ and 6.755±2.966 mg/m³,respectively.It was found that the proportion of the aromatic hydrocarbon from the exhaust of the gasoline vehicles was larger than that of the diesel vehicles,maybe it’s because there are more aromatic hydrocarbon additives in the gasoline.The average emission concentrations of TVOCs from China III,China IV and China V are 8.540±1.399mg/m³,5.858±3.454mg/m³ and 5.320±1.878mg/m³,respectively.With the tightened emissions standards,the emission concentration of the TVOCs decrease and the proportion of aromatic hydrocarbons and nitroxide compounds increase and the proportion of olefins decrease.The average concentration of TVOCs from gasoline vehicles under low-speed and high-speed conditions are 11.229±1.372 mg/m³ and 5.569±0.287 mg/m³,respectively.The proportion of aromatic hydrocarbons from gasoline vehicles under low-speed conditions is greater than that in high-speed conditions.The average concentration of TVOCs from diesel vehicles under low-speed and high-speed are 8.523±3.824 mg/m³ and 5.517±2.218 mg/m³.The proportion of VOCs in diesel vehicles under different speed conditions has little change.2.Combined with the concentrations of VOCs and the vehicle driving data recorded by the PEMS system,the average emission factors of total VOCs emitted by gasoline vehicles and diesel vehicles are 5.343±2.216 mg/km and 33.908±22.679 mg/km,respectively.The average EFs of TVOCs from China III,China IV and China V vehicles are 21.730±18.602mg/km,19.362±28.892mg/km and 9.140±7.168mg/km respectively.With the tightened emissions standards,the EFs of total VOCs decrease.Strict emission standards and elimination of old vehicles are conducive to reducing VOCs emissions.The average EFs of TVOCs from gasoline vehicles under low-speed and high-speed conditions are 12.679±2.300 mg/km and 5.072±0.379 mg/km,respectively.The average EFs of TVOCs from diesel vehicles under low-speed and high-speed are 54.055±41.485mg/km and24.011±13.576mg/km,respectively.Keeping roads smooth and relatively high-speed operation of vehicles is conducive to reducing VOCs.3.The PM emission factor of 11 vehicles is obtained.by weighing the filter membranes.It was found that the emission factor of the particulate matter was related not only to the emission standard and fuel type but also to the mileage of the motor vehicle,engine displacement and vehicle maintenance.Through the analysis of the emission rate of different speed segments,it was found that the emission rate of particulate matter was positively correlated with the velocity.The increase of velocity will increase the emission of particulate matter of motor vehicles to a certain extent,but the peak of the emission rate of each motor vehicle is related to the engine’s own characteristics and the operating environment conditions of the motor vehicle.4.Through the analysis of water-soluble ions,inorganic elements and carbonaceous components in the particles,it was found that the ratio of organic carbon（OC）/element carbon（EC）of gasoline vehicles was greater than the ratio of OC/EC of diesel vehicles.,indicating the proportion of organic carbon in the carbonaceous component from gasoline vehicles’exhaust was larger than that of diesel vehicles.The top 4 emission factors of water-soluble ions from vehicles’exhaust are Cl^-,SO₄^2-,Ca²⁺and Na⁺,and the top 8 emission factors of inorganic elements from vehicles’exhaust are K,Na,Ca,Mg,Sr,Fe,Zn,Pb,hich are mainly derived from fuel additives and engine wear.the most common component of fine particle composition are OC and EC,followed by water-soluble ions,and the least proportion is inorganic elements.Among the particle composition spectrum,the most proportion is OC and EC,followed by water-soluble ions,and the least proportion is inorganic.