AAAR 31st Annual Conference
October 8-12, 2012
Hyatt Regency Minneapolis
Minneapolis, Minnesota, USA
Abstract View
Secondary Organic Aerosol Formation from Dilute Small Off-Road Engine Emissions
DANIEL S. TKACIK, Albert A. Presto, Allen Robinson, Carnegie Mellon University
Abstract Number: 709 Working Group: Carbonaceous Aerosols in the Atmosphere
Abstract Internal combustion engines are a major source of particulate matter (PM) in urban areas. A complex mixture of organics contributes 20 – 90% of fine PM mass. Organic PM results from emission of primary organic aerosol (POA) and formation of secondary organic aerosol (SOA). Small off-road engines (SOREs) are one class of sources that have been subject to much less regulation and therefore are much more polluting than on-road sources. For example, nearly 11% of total US hydrocarbon emissions come from handheld two-stroke engines (EPA 2005), even though these engines account for very little in terms of national fuel consumption.
In this study, we investigate SOA formation from dilute two-stroke and four-stroke SORE emissions via photo-oxidation under a range VOC:NOx ratios. Particle number and volume concentrations are measured using a scanning mobility particle sizer (SMPS) and particle composition is measured using an Aerodyne high-resolution aerosol mass spectrometer (HR-AMS). Gas-phase measurements are made using an online gas-chromatograph with a mass selective detector (GC-MS). SOA/POA ratios from both types of emissions range from 0.11 to 22. POA and SOA mass spectra are separated using positive matrix factorization (PMF). SOA resulting from the photo-oxidation of two-stroke SOA SORE exhaust is found to be more oxidized than SOA from four-stroke exhaust. SOA production from dilute two-stroke SORE emissions, which is calculated on a fuel-consumption basis, is found to be orders of magnitude larger than most on-road sources. This suggests that SOREs, especially two-stroke engines, may be a significant source of SOA.