Michael M. Rhead

Survival of polycyclic aromatic hydrocarbons during diesel combustion

The application of a radiotracer technique to investigate the sources of polycyclic aromatic hydrocarbons (PAH) in diesel exhaust emissions is described. In separate experiments, 14 C-radiolabeled naphthalene, 2-methylnaphthalene (2-MeNp), fluorene, pyrene, and benzo[a]pyrene (B[a]P) were each added to diesel fuel, which was combusted in a 2-L direct injection Perkins Prima diesel engine. Exhaust samples were collected using a novel exhaust gas sampling device designed for sampling organic species in automobile exhaust emissions. Survivals for these PAH were 0.87% for fluorene, 0.54% for 2-MeNp, 0.47% for naphthalene, 0.17% for pyrene, and 0.04% for B[a]P. A linear relationship was observed between the extent to which individual PAH survived combustion and the energy level of the lowest unoccupied molecular orbital (LUMO) of the molecule. LUMO energy levels for each molecule were calculated from Huckel molecular orbital theory. The relationship observed in the current experiment suggests that, forthese PAH and under steady-state engine conditions, it is the chemical kinetics of reactions occurring in the combustion chamber as opposed to thermodynamic stabilities that determine the extent of PAH survival during diesel combustion. Using this relationship, it should be possible to predict the extent of PAH survival in diesel emissions from a knowledge of the PAH composition of the fuel.

Polycyclic aromatic compound profiles from a light-duty direct-injection diesel engine

The exhaust from a direct-injection light-duty diesel engine was sampled for polycyclic aromatic compounds (PAC) at three constant speeds and at five load settings for each speed, using a total-exhaust solvent-stripping apparatus. Exhaust samples were analysed for 3- and 4-ring polycyclic aromatic hydrocarbons (PAH) and dibenzothiophene by g.c.-m.s. in electron-impact mode. The PAC recoveries (per cent of fuel PAC) were highest at low loads and progressively declined with increasing load. At 1000 rev min−1 the averaged recoveries of four PAC (fluorene, dibenzothiophene, phenanthrene and pyrene) decreased from 0.95% at low load to 0.2% at full load. The recoveries of all PAC converged at high load, indicating survival of fuel PAC unchanged. A greater range of PAC recoveries was found at low loads, e.g. the recovery of pyrene at 1% of full load was significantly higher than that of other PAC. At 3000 rev min−1 the combustion efficiencies were greater and average PAC recovery decreased from 0.47% at low load to 0.13% at full load. The range of PAC recoveries at low load was greater at higher speeds. The difference between the percentage recoveries of dibenzothiophene and fluorene on the one hand and their monomethyl derivatives on the other was also most marked at high speed and low loads. The increased range of recoveries at high speed may be due either to pyrosynthetic contributions or to a range of combustion efficiencies of individual PAC structures.

The sources of benzo[a]pyrene in diesel exhaust emissions

Abstract Results are presented for the combustion of diesel fuel spiked with [7,10- 14 C]benzo[ a ]pyrene in a Perkins Prima DI diesel engine. Diesel exhaust samples were collected using the Total Exhaust Solvent Scrubbing Apparatus (TESSA) sampling system. Analysis of the exhaust samples was performed by radio-high performance liquid chromatographic techniques developed for this research. The major radioactive species in the exhaust was identified as [ 14 C]benzo[ a ]pyrene which had survived combustion. The survival was 0.04% of the original activity. The initial specific activity of the radiochemical in the fuel (248 μCi/mg) was similar to that in the exhaust (200 μCi/mg). It was concluded that benzo[ a ]pyrene in the fuel surviving combustion was the major source of benzo[ a ]pyrene in the exhaust. Contributions from other sources including lubricating oil and pyrosynthetic formation within the combustion chamber amounted to no more than 20%.

Initial studies on the application of high-performance liquid chromatography to determine organocopper speciation in soil-pore waters

The use of reversed-phase high-performance liquid chromatographic techniques with molecular- and atomic-spectroscopic detectors to determine organocopper complexes in soil-pore wate is described. Polar dissolved organic compounds and associated copper complexes are separated using either a single Hypersil ODS column or two Hypersil ODS columns and a Hamilton PRP 1 column in series. Quantification was achieved using ultraviolet detectors for the organic molecular species and graphite furnace atomic-absorption spectrometry for the copper.

A POROUS CARBON FILM FOR THE COLLECTION OF ATMOSPHERIC AEROSOL FOR TRANSMISSION ELECTRON MICROSCOPY

This paper describes a method of direct sampling of fine urban aerosol using porous carbon films, to increase collection efficiency and retain the structural integrity of the aerosol. A nuclepore membrane filter was coated with carbon and washed with chloroform to leave a clean porous carbon film on a 200‐mesh transmission electron microscope copper grid. The grid was attached to a clean nuclepore filter using carbon cement. Sampling was conducted for 1 h at 1.9 L min−1 flow rate. The porous carbon grid with sample was then assayed using transmission electron microscopy, and negatives were suitable for image analysis. The collection of fine airborne particles using this method is appropriate for electron microscopy, with a minimum of interference to the structure of collected particles.

Diesel combustion of an alkylated polycyclic aromatic hydrocarbon

The combustion of an alkylated PAH in a direct-injection diesel engine has been investigated using a low-aromatic diesel fuel spiked with 2- and 3-ethylphenanthrene. Exhaust samples were collected using a total exhaust solvent stripping apparatus (TESSA). The 2- and 3-ethylphenanthrene were recovered in yields of 0.3 and 0.35 wt% respectively. The major product from the combustion of ethylphenanthrene was shown to be vinylphenanthrene, produced in a yield of 0.01 wt% of the total added ethylphenanthrene. Although there was no increase in the emission of phenanthrene or other PAH, a statistically significant increase in the emission of 3-methylphenanthrene was observed. These results suggest that for these isomers, under the engine conditions used, no significant dealkylation occurs. The results fit a model based on Dewar reactivity indices, which predicts the extent to which alkyl PAH isomers are dealkylated under pyrolysis conditions.

The contribution of lubricating oil to diesel exhaust emissions

Abstract A new method has been developed for assessing the lubricating oil contribution to diesel exhaust particulates involving a computer program which creates data sets from the integrator output of high resolution gas chromatography (HRGC) analyses of sump oil and exhaust samples. The computer matches up to 60 peaks and enables the presence of lubricating oil in an exhaust sample to be quantified. Samples of diesel exhaust were used to develop the method and the lubricating oil contribution to exhaust emissions was calculated to be 0.6 – 1.0 g/hr which represented 28% of the total particulates.

Investigation of the fate of specific hydrocarbon fuel components in diesel engine combustion

Abstract A technique is described whereby, in separate experiments, [ 14 C]octadecane and [ 14 C]benzene were added as part of the fuel to a diesel engine and radiolabelled products of combustion examined by radio-GC. In an attempt to elucidate specific products of combustion [ 13 C]benzene was included with the [ 14 C]benzene so that 13 C-products of combustion could be sought by GC-MS. Recovered radioactivity from the exhaust was 0.002% for the benzene combustion and 0.008% for the octadecane combustion. Octadecane itself was recovered in a yield of 9 × 10 −4 %.

The use of bromophenol blue as a tracer in sewage works

Abstract A reliable method for the quantitative assessment of water mixing in sewage works is presented. Using a rapid visible-spectroscopic technique to assay Bromophenol Blue, both laboratory and in situ adsorption/degradation studies are presented which confirm that this dye may be used quantitatively in tracer experiments.

The use of uric acid as a method of tracing domestic sewage discharges in riverine, estuarine and coastal water environments

Abstract The chemical tracking of sewage effluents discharged into fresh and saline waters presents difficulties, especially in estuaries. The main difficulty is caused by the dissolved constituents being used to monitor the effluent also occurring naturally at similar levels. Uric acid is present at significant levels in untreated sewage and is not normally found in unpolluted waters. Until now no suitable routine method has been available for uric acid estimation in fresh and saline waters at levels normally encountered in the environment. In this paper we describe a recently developed technique using high-performance liquid chromatography which estimates uric acid in both fresh and saline waters in the range 1–10,000 μg l −1 with a precision (2σ) of ±20% at 2 μg l −1 , ±4% at 40 μg l −1 and ±2% at 10 mg l −1 .