Chemical Analysis of Diesel Engine Nanoparticles Using a Nano-DMA/Thermal Desorption Particle Beam Mass Spectrometer

Abstract

Diesel engines are known to emit high number concentrations of nanoparticles (diameter < 50 nm), but the physical and chemical mechanisms by which they form are not understood. Information on chemical composition is lacking because the small size, low mass concentration, and potential for contamination of samples obtained by standard techniques make nanoparticles difficult to analyze. A nano-differential mobility analyzer was used to size-select nanoparticles (mass median diameter approximately 25-60 nm) from diesel engine exhaust for subsequent chemical analysis by thermal desorption particle beam mass spectrometry. Mass spectra were used to identify and quantify nanoparticle components, and compound molecular weights and vapor pressures were estimated from calibrated desorption temperatures. Branched alkanes and alkyl-substituted cycloalkanes from unburned fuel and/or lubricating oil appear to contribute most of the diesel nanoparticle mass. The volatility of the organic fraction of the aerosol increases as the engine load decreases and as particle size increases. Sulfuric acid was also detected at estimated concentrations of a few percent of the total nanoparticle mass. The results are consistent with a mechanism of nanoparticle formation involving nucleation of sulfuric acid and water, followed by particle growth by condensation of organic species.

Characterization of urban and rural organic particulate in the Lower Fraser Valley using two Aerodyne Aerosol Mass Spectrometers

“…The diesel exhaust spectrum was compared to laboratory generated diesel fuel and lubricating oil spectra and the study concluded that under most operating conditions the organic carbon fraction of in-use diesel vehicle exhaust aerosol is dominated by the recondensed vapour from the evaporated engine lubricating oil. These findings were similar to those found by Tobias et al (2001), which concluded that the dominant organic components of fuel and lubricating oil are n-alkanes, branched alkanes, cycloalkanes, and aromatics (including polyaromatic hydrocarbons). All spectra were dominated by the ion series C n H þ 2nþ1 (m/z 29, 43, 57, 71, 85,y), which is typical of saturated normal and branched alkanes.…”

Determinants of ultrafine particle exposures in transportation environments: findings of an 8-month survey conducted in Montréal, Canada

“…Indeed, lower UFP exposures were expected at increased wind speeds owing to the dispersion of vehicular emissions, and the observed inverse correlation between ambient temperature and UFP exposures was not surprising as the formation of UFPs from traffic exhaust depends in part on vapor condensation (Korhonen et al, 2004;Kulmala et al, 2004) which is favored at lower temperatures. Specifically, some evidence suggests that organic compounds from unburned fuel and lubricating oil are involved in the formation of UFPs from vehicle exhaust (Tobias et al, 2001;Sakurai et al, 2003).…”

Measuring Particulate Mass Emissions with the Electrical Low Pressure Impactor

“…The precise value of σ nuc is unimportant and could just as well be set to unity since the majority of particles in the nucleation mode will have aerodynamic sizes below the lowest impactor stage. The density can be adjusted lower in the event that the nucleation mode is predominantly hydrocarbon in origin, as with heavy duty diesel engines (Tobias et al 2001), or higher in the case of high sulfate content, as suspected for light duty diesels (Scheer et al 2005).…”