Peter F. Nelson

The hydrocarbon composition of exhaust emitted from gasoline fuelled vehicles

Abstract The non-methane hydrocarbon (NMHC) compositions of the exhausts from 67 vehicles in ‘on the road’ condition and driven through an urban driving cycle on a chassis dynamometer, have been determined. The major components were ethylene (11.2% w/w of NMHC), toluene (10.2%), acetylene (8.7%), m , p -Xylenes(6.5%), benzene (5.0%), propylene (5.0%) and i -pentane(4.8%). These compounds have also been reported as significant components in the exhausts from two similar populations of American vehicles. The NMHC compositions were found to be insensitive to the mass emission rates of hydrocarbons from the vehicles, except for the combustion-derived olefins, ethylene and propylene, which were affected by engine modifications introduced to satisfy emission control requirements. A close relationship was found between petrol composition and exhaust composition but this did not correspond simply to emissions of unburnt petrol. The aromatics are enriched relative to the alkanes in exhaust when compared with their proportions in the petrol.

Formation and fate of PAH during the pyrolysis and fuel-rich combustion of coal primary tar

The formation and fate of polycyclic aromatic hydrocarbons (PAH) during the pyrolysis and fuel-rich combustion of primary tar generated under rapid heating conditions have been studied. Experiments were performed using a quartz two-stage reactor consisting of a fluidized-bed reactor coupled to a tubular-flow reactor. Primary tar was produced in the fluidized-bed reactor by rapid coal pyrolysis at 600°C. The freshly generated tar was subsequently reacted in the tubular-flow reactor at 1000°C under varying oxygen concentrations covering the range from pyrolysis to stoichiometric oxidation. PAH species present in the tars recovered from the tubular-flow reactor were analyzed by high-performance liquid chromatography (HPLC). Twenty-seven PAH species, varying from 2-ring to 9-ring structures, were identified, including benzenoid PAH, fluoranthene benzologues and indene benzologues. The majority of PAH species identified from pyrolysis were also identified in the samples collected from oxidation experiments. However, three products, 9-fluorenone, cyclopenta[def]phenanthrene and indeno[1,2,3-cd]fluoranthene, were produced only during oxidizing conditions. The addition of a small amount of oxygen brought about measurable increases in the yields of the indene benzologues and 9-fluorenone, but the yields of all PAH products decreased at high oxygen concentrations, in accordance with their destruction by oxidation. Possible formation and destruction mechanisms of PAH under fuel-rich conditions have been discussed.

Sources of atmospheric hydrocarbons in Sydney: A quantitative determination using a source reconciliation technique

Abstract The relative strengths of the sources of atmospheric hydrocarbons in Sydney have been determined by a source reconciliation technique, which involved the detailed characterization of the compositions of the major hydrocarbon sources and about 150 determinations of the concentrations of numerous individual hydrocarbons in the air. The principal sources of atmospheric hydrocarbons are shown to be vehicle exhaust ( 36 ± 4% w/w of non-methane hydrocarbons), evaporative emissions of petrol ( 32 ± 4 % w/w) and evaporation of hydrocarbon and other solvents ( 23 ± 4 % w/w). The reliability of the results is confirmed by an analysis of the sensitivity of the source strength calculations to uncertainties in the source compositions and in the atmospheric concentrations, and to the reactivity of the hydrocarbons. The relative source strengths are compared with an inventory of hydrocarbon emissions in Sydney carried out by the State Pollution Control Commission. The results obtained by the two techniques agree well, except for petrol evaporation for which the source reconciliation method indicates a somewhat higher contribution.

The m,p-xylenes:ethylbenzene ratio. A technique for estimating hydrocarbon age in ambient atmospheres

Measurement of the relative concentrations of the aromatic isomers m, p-xylenes and ethylbenzene is proposed as the basis of a technique for estimating hydrocarbon age in ambient atmospheres. These compounds are shown to be present in constant proportion in the major anthropogenic sources of hydrocarbon emission in Sydney and this is probably also the case in at least some other urbanized regions. Differences in photochemical reactivity cause the isomers to disappear from the atmosphere at notably different rates, a fact which is confirmed by experiments with large outdoor smog chambers. n nApplication of the technique is illustrated by field measurements designed to clarify the importance of recirculation of previous days emissions on the formation of photochemical smog in the Sydney area.

Exposure to emissions of 1,3-butadiene and benzene in the cabins of moving motor vehicles and buses in Sydney, Australia

Abstract Concentrations of 1,3-butadiene and benzene have been measured inside the cabins of both pre-1986 (non-catalyst-equipped) and post-1986 (catalyst-equipped) vehicles on freeway and urban driving routes around Sydney, Australia. Mean in-vehicle concentrations of 1,3-butadiene and benzene observed for the newer cars during the morning peak-hour were 5.5 ± 2.l and 22.1 ± 4.1 ppb respectively. Corresponding values for the older, poorly maintained vehicle were 11.5 ± 3.0 and 48.1 ± 6.9 ppb, respectively, about double those of newer vehicles. 1,3-Butadiene was only observed at significant concentrations inside the cabins of moving vehicles during peak-hour traffic. Concentrations of this species both in the ambient air, and in the vehicle cabins during freeway trips in non-peak periods, were near or below the detection limit of 0.1 ppb. Therefore, commuter trips are likely to be the major source of exposure to this compound. Both using the airconditioner and driving with the vents closed were the most effective ventilation conditions for minimising the exposure to fresh exhaust. For both conditions, trip average in-vehicle concentrations were about 70% of those in the air directly outside the vehicle. For vehicles left in a parking station during the day, exposures to 1,3-butadiene during evening commuter trips were observed to be about 1.2 times those in the morning peak-hour. Concentrations of volatile organic compounds measured inside buses were about 50% of those observed for newer cars.

Conversion of fuel nitrogen in coal volatiles to NOx precursors under rapid heating conditions

Abstract The formation of NO x precursors during the rapid pyrolysis of three Australian coals has been studied by the determination of HCN using long path length Fourier transform infrared spectrometry and of nitrogen-containing species in the tars using gas chromatography with a nitrogen-specific detector. Significant differences in the release rates of HCN were observed, and these can be reconciled with differences in the composition of the nitrogen fraction of the tars. The stability of the species containing nitrogen in five-membered (pyrrole type) rings is significantly lower than that of species with nitrogen in six-membered (pyridine type) rings. This results in the more rapid formation of HCN from those coals with a greater proportion of nitrogen in pyrrole type structures. At high pyrolysis temperatures (1000 °C), these results suggest that nitrogen released from the decomposition of nitrogen-containing aromatics can be reincorporated into high molecular weight products.

NON-METHANE EXHAUST COMPOSITION IN THE SYDNEY HARBOUR TUNNEL: A FOCUS ON BENZENE AND 1,3-BUTADIENE

The concentrations of individual hydrocarbon species in the Sydney Harbour Tunnel were measured and used to estimate the average composition of emissions from moving motor vehicles in the Sydney urban area. The mean composition of non-methane hydrocarbons in the tunnel air on a weight basis was relatively constant. The mean concentrations for benzene and 1,3-butadiene were 45 and 13 ppbv, respectively, which in turn represented ∼ 5.2% w/w and ∼ 1.0% w/w of the total non-methane C2ue5f8C10 hydrocarbons in the tunnel air. The unit risk factor and the maximum incremental reactivity factor for 1 1,3-butadiene are approximately 30 times higher and 25 times higher, respectively, than the corresponding values for benzene. The concentration (μg m−3) of benzene, however, is only about 5 times that of 1,3-butadiene. On this basis, the relative contribution to the risk associated with exposure to fresh motor vehicle emissions in Sydney would be about 6 times higher for 1,3-butadiene than for benzene. Similarly, the contribution made by 1,3-butadiene to the total hydrocarbon reactivity of the tunnel air will be about 5 times that of benzene. Samples of three different grades of petrol (leaded, unleaded and premium unleaded) from three different brands of fuel were also analysed on two separate occasions. Compositions of leaded and standard unleaded petrol averaged across the three different brands are quite similar. The average aromatic content (% w/w) of the 3 different commercial brands were ∼ 35 and 30% for leaded and unleaded petrol, respectively. However, premium unleaded petrol has a much higher aromatic content of ∼ 47% w/w. Comparison of the petrol and tunnel compositions demonstrated that benzene is enriched relative to other aromatics in exhaust compared to its proportion in the petrol.

Functional forms of nitrogen in coals and the release of coal nitrogen as NOx precursors (HCN and NH3)

The influence of coal nitrogen on the pyrolytic release of NOx precursors, (HCN and NH3), has been investigated for a range of Australian coals. Functional forms of nitrogen in the coals were determined by X-ray photoelectron spectroscopy. Pyrrolic-type nitrogen predominated (50–60% coal nitrogen), but pyridinic and quaternary forms were also detected. The proportion of pyridinic increased and that of quaternary decreased with increasing carbon contents of the coals. Four coals, ranging in rank from brown to bituminous and in nitrogen content from 0.6–2.0%, dry ash free basis, were pyrolyzed in a fluidized bed reactor at temperatures ranging from 500 to 1100°C, gas residence times of 0.3–0.5 s and particle heating rates of 104 K s−1. Formation of HCN and NH3 occurred at higher temperatures than that required for maximum tar yields; cracking reactions of the tars are a probable source of HCN and NH3. However, the results show that release of nitrogen from structures which are not volatilised as tar also occurs. The major nitrogen-containing components of the tars were identified and quantified by gas chromatography. Nitrogen contained in pyridinic groups was more stable than that in pyrrolic groups; thus, a higher pyrolysis temperature was necessary to release nitrogen as HCN and NH3 from the pyridinic groups. For the range of coals and pyrolysis conditions studied here, however, nitrogen release (as a proportion of total coal nitrogen), in the form of NOx precursors, did not depend on coal type or coal nitrogen content.

Speciated hydrocarbon profiles and calculated reactivities of exhaust and evaporative emissions from 82 in-use light-duty: Australian vehicles

Mass emissions of non-methane hydrocarbon (NMHC) from 26 pre-1986 and 56 post-1985 catalyst-equipped in-service vehicles were determined from measurements made on a chassis dynamometer using an urban drive cycle. Evaporative emissions were measured on a subset (4 pre-1986 and 8 post-1985) of these vehicles. Average ADR emissions (mg/km) of the individual HCs from the older pre-1986 vehicles were generally 4–7 times the emissions from newer catalyst-equipped vehicles. Evaporative emissions from the older vehicles are also much higher than those of newer vehicles. Exhaust from newer catalyst-equipped vehicles had lower proportions of substituted aromatics and alkenes and higher proportions of lower molecular weight alkanes. The effect of fuel type on the exhaust emissions was also investigated by refuelling 9 of the pre-1986 vehicles with both unleaded and leaded petrol. A 20–40% reduction in HC mass emissions was observed when unleaded petrol was used instead of leaded petrol. Reactivities of the emissions and the contributions from different classes of compounds are also reported. The specific reactivity of the exhaust emissions from newer vehicles was lower than that for older vehicles owing to the smaller proportions of highly reactive alkenes and substituted aromatic species. Moreover, as older vehicles have higher average mass emissions, when considered on a per-km basis, the pre-1986 vehicles have a greater ozone-forming potential than post-1985 vehicles. The specific reactivities of the NMHC (gO3/gNMHC) of both the heat build and hot soak evaporative emissions were much lower than the exhaust emissions.

Measurements of kinetic isotope effects and hydrogen/deuterium distributions over methane oxidative coupling catalysts

The kinetic isotope effect for CH4 compared to that for CD4 has been measured for the oxidative coupling reaction of methane over LiMgO, SrCO3, and Sm2O3 catalysts in a flow reactor. Each catalyst gave results consistent with Cue5f8H bond breaking being the slow step. For temperatures between 680–780 °C over LiMgO, kHKD decreased slightly with temperature. The isotope effect for ethane production was more sensitive to the level of conversion and declined from 1.8 at low conversion to near unity under conditions where the ethylene to ethane ratio was high (~1). Selectivities to hydrocarbons were lower with CD4 and did not change with decreased flow rates, implying that either COx and C2 products arise by totally separate slow steps or, if a common step with CH3 radicals is involved, then COx formation occurs on the catalyst. Experiments with CH4CD4 mixtures showed that CH3CD3 and CH2CD2 were the dominant mixed products. The distribution of the ethanes always reflected the relative concentrations of CH3 and CD3 determined by the kinetic isotope effect. At low ethylene to total C2 ratios (~0.2) this was also true for ethylene; but at higher ratios substantial exchange to produce ethylenes other than C2H4, CH2CD2, and C2D4 occurred. The concentration of the exchanged methanes correlated with total methane conversion but was dependent on the surface. Exchange in the ethylenes also correlated with exchange in the methanes and purely gas phase processes appear at least partially responsible. H2: HD: D2 ratios are always at equilibrium and exchange also occurs between CD4 and H2.