The Emissions of Intermediate-volatility and Semi-volatile Organic Compounds from Chinese Diesel Vehicles under Different Engine Conditions

XIAO ZHANG, Tsinghua University

     Abstract Number: 695
     Working Group: Meet the Job Seekers

Abstract
Intermediate volatility organic compounds (IVOCs) emerge as significant potential SOA contributors in recent works. IVOCs are chemical compounds with effective saturation concentration between 103 and 106 μg/m3, which generally corresponds to the volatility range of C12 -C22 n-alkanes. The smog chamber experiments illustrated that the majority of SOA is contributed by IVOCs aging processes. The IVOCs emitted from diesel vehicles contribute 30% of the total SOA in London. More than 50% SOA produced by mobile sources, which is the largest source contributor of organic aerosol in Southern California, is originated from the oxidation of IVOCs.

Many researches have shown that the I/SVOC chemical composition and volatile distribution of mobile sources depend on the fuel type, engine load, and aftertreatment technology. IVOC emissions are highly dependent on engine power, with highest emissions at engine idle. With the increasing of engine load, engine combustion efficiency is continuously improved, and gaseous and particle I/SVOC emissions are gradually reduced. Compared with idle conditions, the gas-phase I/SVOC emission factors under 100% engine load decreased 72%-76%. At low load operations, the chemical composition of I/SVOC dominated by saturated hydrocarbon species. With engine load increased, IVOC become increasingly characterized by unsaturated hydrocarbons and oxygenated organics. The proportion of aromatic hydrocarbons in IVOCs increased with a higher load. With the increase of engine load, the saturation of gaseous I/SVOC decreases gradually. The proportion of saturated hydrocarbons (alkanes+ cycloalkanes) decreased from 61% to 40%. The proportion of unsaturated substances (olefin + aromatic hydrocarbon +OVOC) increased from 39% to 60%. The proportion of oxygen compound emission increased with the increase of engine load, which is newly formed in the incomplete combustion process when the engine temperature and pressure rise.

We discovered that chemical composition and volatility distribution measured I/SVOC emissions during engine idle operating conditions that were similar to diesel fuel which indicated that gaseous I/SVOC emission at low load is mainly from the direct volatilization of unburned diesel. The compositions of IVOCs were not consistent with diesel fuel under high loads which indicated that different formation pathways of IVOCs exist for different engine loads. At high load, other sources of IVOC will become the main source, which may be the pyrolysis of lubricating oil or diesel oil at high temperature.