10th International Aerosol Conference September 2 - September 7, 2018 America's Center Convention Complex St. Louis, Missouri, USA
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Comparing On-Road and Laboratory Measurements of Primary Emissions and Secondary Aerosol Formation Potential of Individual Light-Duty Vehicles
Pauli Simonen, Joni Kalliokoski, Panu Karjalainen, MIIKKA DAL MASO, Topi Rönkkö, Sanna Saarikoski, Minna Aurela, Matthew Bloss, Hilkka Timonen, Georgios Triantafyllopoulos, Athanasios Dimaratos, Leonidas Ntziachristos, Zissis Samaras, Jorma Keskinen, Tampere University of Technology
Abstract Number: 1229 Working Group: Combustion
Abstract Internal combustion engine powered vehicles produce exhaust particulate and gaseous pollutants that both affect climate and human health. Some of the emitted gaseous pollutants may produce secondary particulate mass in the atmosphere, as a consequence of atmospheric oxidation. Such secondary processes are often absent when estimating the contribution of transport to urban pollution using emission factors (EFs). Such EFs are most frequently expressed as mass of pollutant in the exhaust, normalized to the distance or fuel consumption of the vehicle concerned.
The EFs can be obtained from laboratory experiments on a chassis dynamometer or during on-road driving. While the laboratory results are highly reproducible because of the controlled environment and precisely defined vehicle operation, the emissions during engine laboratory driving cycles do not necessarily represent the emissions in real-world driving.
Here, we compare the EFs obtained from laboratory driving cycles to the ones obtained from on-road chase experiments for two EURO 6 light-duty vehicles, comprising a direct injection gasoline vehicle and a port fuel injection gasoline vehicle. In addition, on-road EFs are presented for a diesel particulate filter equipped EURO 6 light-duty vehicle. In the laboratory, NEDC and WLTC driving cycles were run on a chassis dynamometer. NOX, CO, CO2 and HC concentrations were measured utilizing a constant volume sampler (CVS).
During the on-road experiments, the vehicle was trailed by a mobile laboratory at a racing track where different driving patterns, including random driving were performed. For particle characterization, the mobile lab was equipped by a condensation particle counter (CPC) for particle counting. In addition, a combination of a CPC and a particle size magnifier (PSM) was used to determine the concentration of particles smaller than 3 nm in diameter. The chemical composition of the particles was measured with a soot-particle aerosol mass spectrometer (SP-AMS). Two electrical low-pressure impactors (ELPI) were used to measure the particle size distribution, and also particle mass concentration was calculated from the size distribution data. The second ELPI was measuring downstream of an oxidation flow reactor (TUT Secondary Aerosol Reactor; TSAR) to determine the secondary aerosol formation potential. In TSAR, the sample is oxidized by ozone and OH radicals, simulating atmospheric oxidation. Gas-phase emissions were measured with CO2 and NOX analyzers. In addition, a commercial portable emission measurement system (PEMS) was deployed during the on-road measurements to measure raw exhaust CO2, NOX and CO concentrations.
This study presents laboratory and on-road EFs for particle number and mass emissions, as well as the secondary aerosol production factor for the two EURO 6 gasoline light-duty vehicles, and the on-road EFs for the EURO 6 diesel vehicle. The effect of driving condition in both laboratory and on-road experiments is studied. Finally, the study discusses different methods to obtain the EF from the on-road experiment and their sensitivity to background effects.