10th International Aerosol Conference September 2 - September 7, 2018 America's Center Convention Complex St. Louis, Missouri, USA
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Effect of High-Speed Driving Conditions on SOA Formation Potential from GDI Vehicle
NIINA KUITTINEN, Stephen Zimmerman, Weihan Peng, Cavan McCaffery, Patrick Roth, Pauli Simonen, Jorma Keskinen, Topi Rönkkö, Roya Bahreini, David R. Cocker III, Georgios Karavalakis, Tampere University of Technology
Abstract Number: 1619 Working Group: Combustion
Abstract Aerosol particles from vehicle emissions are one the main contributors to impaired air quality and visibility in urban areas. It has been shown that, in many cases, the mass of secondary organic aerosol (SOA) formed as a result of photochemical oxidation of exhaust vapors in the atmosphere exceeds the emitted primary particulate matter. Traditionally, secondary aerosol formation potential has been studied using environmental chambers into which exhaust sample is collected throughout a transient driving cycle. Recently, some studies applying flow-through type oxidation reactors have indicated that SOA formation is highly dependent on vehicle driving condition. In these studies, well-established driving cycles such as the NEDC have been investigated. However, the ability of cycles like NEDC or the FTP to represent real-world driving conditions has been questioned, and some new driving cycles have been developed that better mimic the driving patterns in urban areas and freeways. In this study, the SOA formation potential of a modern GDI vehicle is examined over a variety of drive cycles representing different driving conditions.
Testing was conducted over duplicate cold-starts FTP, NEDC, and LA92 cycles and over duplicate hot-starts US06, Highway Fuel Economy Test (HWFET), and a set of cycles developed by the California Department of Transportation (Caltrans). The Caltrans cycles were developed to represent realistic driving conditions in California roads and characterized by high speeds (65 mph to 75 mph) and lower speeds (0 mph to 60 mph). Testing was performed on a GDI light-duty vehicle equipped with a wall-guided injection system and operating on typical California E10 fuel. Primary emissions measurements included gaseous pollutants, total and solid particle number, black carbon, and particle size distributions. The atmospheric aging of the emissions was studied using two parallel methods. TUT Secondary Aerosol Reactor (TSAR), a laminar oxidation flow reactor that allows real-time characterization of secondary aerosol formation, was applied for online measurements during the driving cycles. In addition, exhaust sample was injected to UC Riverside’s Mobile Atmospheric Chamber (MaCh) to compare the average SOA forming potential over one completed cycle, as well as to gain in-depth information on the formation process. The secondary aerosol was characterized using scanning mobility particle sizer (SMPS), volatility DMA (VDMA), and aerosol particle mass analyzer (APM), combined with high resolution time-of-flight aerosol mass spectrometer (HR-ToF-AMS) for bulk chemical composition. For the real-time oxidation with the TSAR, an electrical low pressure impactor (ELPI+) and a mini aerosol mass spectrometer (mAMS) were applied to measure real-time secondary particle mass, as well as bulk chemical composition of the SOA, respectively. The observations made during this study underline the effects of varying driving patterns on the SOA formation from GDI vehicles and allow comparison of SOA results between an atmospheric chamber (batch testing) and an oxidation flow reactor (real-time testing).