AAAR 32nd Annual Conference
September 30 - October 4, 2013
Oregon Convention Center
Portland, Oregon, USA
Abstract View
Primary Emissions Measurements and Secondary Organic Aerosol Formation Experiments Provide Insight to the Atmospheric Burden of Particulate Matter from Mobile Sources
ANDREW MAY, Timothy Gordon, Shantanu Jathar, Albert A. Presto, Allen Robinson, Carnegie Mellon University
Abstract Number: 375 Working Group: Urban Aerosols
Abstract Mobile sources such as gasoline cars and diesel trucks emit a complex array of gas- and particle-phase organic material into the atmosphere that may contribute substantially to air pollution. Emissions include primary organic aerosol (POA), elemental carbon (EC), and organic vapors. Measurements of primary emissions are relative straightforward during source testing, while apportionment of pollutants to gasoline and diesel sources has been a topic of debate. Incorporating the formation of secondary organic aerosol (SOA) into apportionment estimates introduces even more uncertainty. Recent work has established two competing hypotheses: either gasoline vehicles dominate ambient SOA production from mobile sources or diesel vehicles do. Source attribution of SOA is further complicated due to varying regulations and fleet composition. Through comprehensive source testing, we have measured primary particulate matter (PM = POA + EC) and SOA precursors from an in-use fleet of on-road gasoline and diesel vehicles. These tests were coupled with environmental chamber experiments that quantified SOA production rates. We input distributions of measured PM emissions and SOA production rates into a Monte Carlo simulation to estimate the relative importance of gasoline and diesel vehicles to total ambient PM (primary + secondary) as a function of fuel consumption. Through our simulations, we find that while on-road diesel vehicles are the major contributor to primary PM, SOA production from on-road gasoline vehicles based on our chamber-derived yield values dominates the SOA budget from these two sources. For example, gasoline vehicles will be the dominant source of atmospheric PM from on-road sources as long as the vehicle fleet is greater than 60% gasoline on a fuel-consumed basis. The widespread implementation of diesel aftertreatment technologies will significantly reduce both primary PM and SOA precursors from diesel vehicles,; consequently, we predict futuristic vehicle fleets have an even greater quantity of ambient PM attributed to gasoline vehicles.