AAAR 33rd Annual Conference
October 20 - October 24, 2014
Rosen Shingle Creek
Orlando, Florida, USA
Abstract View
Size Distributions and Volatility of Vehicle PM Emissions Measured in a Traffic Tunnel
ALBERT A. PRESTO, Xiang Li, Timothy Dallmann, Carnegie Mellon University
Abstract Number: 155 Working Group: Combustion
Abstract Emissions from motor vehicles are a major source of urban air pollution, including carbonaceous particulate matter (PM) in the form of organic and elemental carbon (OC and EC). Organic PM emissions from both gasoline and diesel vehicles readily evaporate with dilution or mild heating, meaning that populations living near roadways may be exposed to PM with different composition than what is measured in standard dynamometer testing.
This study considers measurements of PM size distributions and PM volatility conducted in a traffic tunnel in Pittsburgh, PA. PM size from 7-400 nm was measured with a pair of scanning mobility particle sizers. PM composition was measured with both filter and continuous measurements of OC and EC, and nonrefractory PM composition was monitored with an Aerosol Chemical Speciation Monitor. PM volatility was investigated using a thermodenuder (TD). The TD operated in two modes: (1) the TD was cycled through low temperature settings between 40-100 C and long residence time (19 sec) to investigate the volatility of organic PM, and (2) the TD was held at high temperature (250 C) and short residence time (3 sec) to quantify the size distribution of nonvolatile PM.
The PM number size distribution peaks at approximately 20-30 nm. Mild heating in the TD causes 10-50% of the organic PM to evaporate. TD modeling using the volatility distributions of May et al (2013) adequately describes the PM evaporation in the TD. High temperature stripping of the PM reveals two nonvolatile modes – one consisting of EC centered at 80-100 nm, and another consisting of particles smaller than 10 nm. The composition of the smaller nonvolatile mode is uncertain, and may contain ash particles resulting from impurities in fuel and lubricating oil.