Origin Identification And Emission Inventory Of Intermediate-Volatility Organic Compound Emissions From Vehicles In China Based On Practical Measurement

In recent years,vehicle emissions have become one of the important emission sources of urban air pollution in China.In the context of coordinated control of regional fine particulate matter and ozone,accurate identification of the highly photochemically active components and precise quantification of vehicle pollution emission inventories have become an effective means to refine air pollution prevention.Intermediate-volatility organic compounds(IVOCs)have the characteristics of high secondary organic aerosol(SOA)yields,high emissions,complex chemical compositions,and active gas-particle partitioning and have significant impacts on air quality,climate change,and human health.However,few studies have simultaneously identified the emission characteristics of gas-and particle-phase IVOCs,which led to their differences in characteristics,main origins,and environmental impacts have not been clarified.Besides,previous studies directly used foreign test data or empirical estimation data to develop IVOCs emission inventory,resulting in large uncertainty of the current IVOCs emission inventory.Given this,we tested 16 on-road vehicles with different emission standards by chassis dynamometer,collected the gas-and particle-phase IVOCs using a thermal desorption solid filled tube(TD tube)and a quartz filter in series,analyzed the experimental samples using a thermal desorption-gas chromatography-mass spectrometry analysis system(TD-GC-MS),and estimated the mass of total IVOCs using a semi-quantitative calculation method.According to the tested results,we estimated the impacts of tightening fuel emission standards on IVOC emissions and potential SOA production,identified the main origins and formation processes of IVOCs emitted from vehicles,and finally,used the locally measured data to develop the speciated emission inventory of IVOCs from vehicles in China for the year of 2018.And therefore,the total IVOC emissions from vehicles and the associated SOA production in each province were evaluated.The key vehicles with large emissions and chemical components were identified.And several measures on control IVOC emissions from vehicles were provided.The main conclusions are as follows:(1)The emission factors of total IVOCs from gasoline and diesel vehicles were 32.9-139.1 mg/kg-fuel and 552.3-2292.5 mg/kg-fuel,respectively.The IVOCs and the associated SOA production for both the gasoline and diesel vehicles did not exhibit a notable drop along with the tightening of the emission standards prior to China VI.(2)The chemical composition and volatility distribution of the gas-phase IVOCs from the gasoline and diesel vehicles were similar to those of their respective fuel content and the chemical composition of the particle-phase IVOCs from the gasoline and diesel vehicles were close to the lubricating oil content.Therefore,unburned/partially burned fuel and lubricating oil were identified as the two main origins of IVOCs emitted from vehicle exhausts.(3)The total vehicular IVOC emissions in China were 216.33 Gg and the total SOA productions were 54.85 Gg in 2018.In terms of provinces,Shandong,Guangdong,Hebei,Henan,and Jiangsu had the largest emissions,contributing 9.58%,7.77%,7.70%,6.62%,and6.07% of total IVOCs emissions,respectively.In terms of vehicle types,the total emissions of trucks were much higher than passenger cars,accounting for 74% of the total emissions;the total emissions of diesel vehicles were much higher than those of gasoline vehicles,accounting for 83% of the total emissions;heavy-duty trucks,light-duty trucks,and small passenger cars were the three largest emission types,accounting for 43.26%,27.47% and 18.89% of the total emissions,respectively.(4)The total emissions of n-alkanes,polycyclic aromatic hydrocarbons,b-alkanes and remaining unresolved complex mixture(UCM)were 26.01 Gg,12.72 Gg,59.68 Gg and 117.92 Gg,respectively.The emissions of unspeciated IVOCs accounted for 82% of the total IVOC emissions.Naphthalene,1-methylnaphthalene,2-methylnaphthalene and fluorene were the most emitted polycyclic aromatic hydrocarbons that were harmful to the human body,with total emissions of 4.36 Gg,3.54 Gg,2.07 Gg,and 1.50 Gg,respectively.(5)Based on the above results,we have proposed several measures to control the IVOC emissions from vehicles,such as accelerating the upgrade of vehicle emission standards,paying attention to the emission reduction of lubricating oil,controlling the emissions of heavy-and light-duty diesel trucks,accelerating the development of vehicle IVOCs control technology,and establishing a long-term effective vehicle exhaust prevention and control mechanism under the policy background of carbon peak and carbon neutrality.