Characterization of particulate matter emissions from on-road gasoline and diesel vehicles using a soot particle aerosol mass spectrometer

T R Dallmann,A H Goldstein,S C Herndon,T W Kirchstetter,E C Wood,J P Franklin,E C Fortner,R A Harley,D R Worsnop,D R Worton,T B Onasch

doi:10.5194/acp-14-7585-2014

Abstract

Abstract. Particulate matter (PM) emissions were measured in July 2010 from on-road motor vehicles driving through a highway tunnel in the San Francisco Bay area. A soot particle aerosol mass spectrometer (SP-AMS) was used to measure the chemical composition of PM emitted by gasoline and diesel vehicles at high time resolution. Organic aerosol (OA) and black carbon (BC) concentrations were measured during various time periods that had different levels of diesel influence, as well as directly in the exhaust plumes of individual heavy-duty (HD) diesel trucks. BC emission factor distributions for HD trucks were more skewed than OA distributions (N = 293), with the highest 10% of trucks accounting for 56 and 42% of total measured BC and OA emissions, respectively. OA mass spectra measured for HD truck exhaust plumes show cycloalkanes are predominate in exhaust OA emissions relative to saturated alkanes (i.e., normal and iso-paraffins), suggesting that lubricating oil rather than fuel is the dominant source of primary organic aerosol (POA) emissions in diesel vehicle exhaust. This finding is supported by the detection of trace elements such as zinc and phosphorus in the exhaust plumes of individual trucks. Trace elements were emitted relative to total OA at levels that are consistent with typical weight fractions of commonly used additives present in lubricating oil. A comparison of measured OA and BC mass spectra across various sampling periods revealed a high degree of similarity in OA and BC emitted by gasoline and diesel engines. This finding indicates a large fraction of OA in gasoline exhaust is lubricant-derived as well. The similarity in OA and BC mass spectra for gasoline and diesel engine exhaust is likely to confound ambient source apportionment efforts to determine contributions to air pollution from these two important sources.

Highlights

On-road motor vehicles, especially those with diesel engines, are important sources of fine particulate matter (PM2.5) emissions (Dallmann et al, 2010)
The ability of the soot particle aerosol mass spectrometer (SP-AMS) to measure black carbon (BC) emitted by motor vehicles was evaluated through a comparison with a collocated MAAP absorption photometer
Black carbon concentrations measured with the MAAP were in good agreement with other approaches used to characterize BC during this field campaign (Dallmann et al, 2012)

Summary

Introduction

On-road motor vehicles, especially those with diesel engines, are important sources of fine particulate matter (PM2.5) emissions (Dallmann et al, 2010). Exposure to PM2.5 has been linked to various negative health effects (Pope and Dockery, 2006; Brook et al, 2010). PM2.5 emissions from motor vehicles are of particular importance in urban areas where emissions occur in close proximity to exposed populations (Jerrett et al, 2005; Brugge et al, 2007).

Objectives

Methods

Results