n-Alkane Profiles of Engine Lubricating Oil and Particulate Matter by Molecular Sieve Extraction

Abstract

As part of the Canadian Atmospheric Fine Particle Research Program to obtain reliable primary source emission profiles, a molecular sieve method was developed to reliably determine n-alkanes in lubricating oils, vehicle emissions, and mobile source dominated ambient particulate matter (PM). This work was also initiated to better calculate carbon preference index values (CPI: the ratio of the sums of odd over even n-alkanes), a parameter for estimating anthropogenic versus biogenic contributions in PM. n-Alkanes in lubricating oil and mobile source dominated PM are difficult to identify and quantify by gas chromatography due to the presence of similar components that cannot be fully resolved. This results in a hump, the unresolved complex mixture (UCM) that leads to incorrect n-alkane concentrations and CPI values. The sieve method yielded better chromatography, unambiguous identification of n-alkanes and allowed examination of differences between n-alkane profiles in light (LDV) and heavy duty vehicle (HDV) lubricating oils that would have been otherwise difficult. These profile differences made it possible to relate the LDV profile to that of the PM samples collected during a tunnel study in August 2001 near Vancouver (British Columbia, Canada). The n-alkane PM data revealed that longer sampling times result in a negative artifact, i.e., the desorption of the more volatile n-alkanes from the filters. Furthermore, the sieve procedure yielded n-alkane data that allowed calculation of accurate CPI values for lubricating oils and PM samples. Finally, this method may prove helpful in estimating the respective diesel and gasoline contributions to ambient PM.

Updating the Conceptual Model for Fine Particle Mass Emissions from Combustion Systems Allen L. Robinson

“…The decrease above C 30 indicates that there are few high-molecular-weight hydrocarbons in the exhaust, mirroring the carbon-number distribution of lubricating oil. 40,41 The fall off below C 20 is likely due to the inability of quartz filters to collect these more volatile organic vapors. In fact, a reasonable fraction (approximately one third) of the lower carbon-number portion of the material collected on quartz filters is likely adsorbed vapors, which is the source of sampling "artifacts" in organic PM sampling.…”

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“…Particles formed by condensation in the diluting exhaust plume are generally in the size range below 30 nm and are formed as the hot exhaust gases are expelled from the tailpipe of a vehicle, creating large numbers of very small particles in the air. They are semi-volatile and consist mainly of hydrocarbons and hydrated sulphuric acid Caravaggio et al, 2007). The conditions influencing the production of these semi-volatile nanoparticles and hence the shape of the particle size distributions, include dilution rate, dilution ratio and temperature.…”