Characteristics Of Formaldehyde Emission From Diesel Vehicles Based On On-line Measurement

The vehicle population in China has been increasing significantly due to the quick development of economy and the urbanization processing.Being a main emission source of amtopsheirc pollution,vehicle exhaust can directly produce formaldehyde（HCHO）gas on one hand,and the alkene species in the exhaust could promote HCHO generation in the atmosphere via atmospheric reaction.As the most abundant carbonyl compound in the troposphere,HCHO is an important source of atmospheric OH radical and plays a key role in the tropospheric photochemical reaction.In addition,HCHO has potential carcinogenic and mutagenic and has been listed in China’s priority control list of toxic chemicals.So far,the quantification of HCHO emissions from vehicle exhaust in China is mostly carried out through the off-line technology of 2,4-dinitrophenylhydrazine tube,which is simple to operate.On-line monitoring of HCHO emissions cannot be achieved,and there is a lack of research to characterize on-road testing of HCHO emissions from vehicles.Therefore,portable emission measurement system（PEMS）combined with an on-line HCHO emission measurement system to carry out chassis dynamometer test and real-world emission test to obtain HCHO emission data of 39 diesel trucks.The main conclusions of this study were showing as follows:（1）The absorption efficiency of on-line HCHO analyzer is 91.4%and the measurement range is 0～600ppbv.The effects of acetaldehyde,NO and NO₂on HCHO signal are 1.4%,0.41%and 2.15%,respectively.The dilution system can achieve a dilution ratio of 0 to 100 times through two-stage dilution.The deviation of the dilution system is-1.0%～3.4%.（2）The emission factors of CO₂,CO,NO_x,HC,CH₄,PN and HCHO of China III to V light-duty diesel trucks,medium-duty diesel trucks and heavy-duty diesel trucks are established basing on the chassis dynamometer test.However,due to the chassis dynamometer test is quite different from on-road test,it is necessary to further carry out the on-road test.（3）The emission factors of CO₂,CO,NO_x,HC,CH₄,PN and HCHO of China III to V light-duty diesel trucks,and heavy-duty diesel trucks are established basing on the on-road test.The emission factors of all pollutants declined with the tightening of emission standards except for the NO_xand HC compounds of light-duty diesel trucks.（4）The HCHO emission rate of light-duty diesel trucks in each VSP mode decreased with the tightening of the emission standard.However,the HCHO emission rate of China III vehicles is higher than that of China VI vehicles.The HCHO emission rate of China IV heavy-duty diesel trucks in each VSP mode is the lowest one,which only accounting for 7.6%and 6.3%of the emission rate of China III and China V.（5）We confirmed that the vehicle load has a great impact on HCHO emission.The HCHO emission factor of highway condition is higher than that of urban condition.The mileage was positively correlated with the HCHO emissions.This study further performed a detailed study on the characteristics of HCHO emission from the diesel truckes and established the corresponding HCHO emission factors under different conditions.This methodology could provide an important reference for the testing and establishing emission factors of unconventional pollutants and will significantly contribute to the development of the vehicle emission model in China.