Title: AIR POLLUTION IN DIESEL BUS GARAGES

Abstract:


Motor vehicles emnit exhaust products which are potentially noxious to a degree which depends on their ultimate concentration in the ambient air. Fitton (1957) has discussed some aspects of air pollution by road transport and has compared the emission of pollutants from petrol and diesel engines; well maintained and properly operated diesel engines emit much less carbon monoxide and unburnt fuel than petrol engines.

 Diesel engines are, however, liable to emit black smoke; in well maintained vehicles this may be limited to a small puff on acceleration, but in others dense black clouds may be emitted, particularly at full load. Kotin, Falk, and Thomas (1955) have reported the presence of carcinogenic hydrocarbons in smoke from an inefficiently operating diesel engine. Other potentially harmful exhaust products include oxides of nitrogen and aldehydes; these are emitted in similar concentrations by both petrol and diesel engines. 

Though much analytical work on the composition of motor exhausts has been published, relatively little is known about the concentrations of pollutants (other than carbon monoxide) which traffic may produce in the air men breathe; without this information it is difficult to make any reasonable assessment of possible hazards to health. The work reported in this paper is the first part of a larger attempt to fill this deficiency in our knowledge of air pollution. We have studied air pollution in diesel bus garages where there are clearly defined groups of men who are regularly exposed to relatively high concentrations of exhaust products. In some cases the same men have been employed on similar work over long periods and sickness records are available. 

Raffle (1957) has studied the deaths, retirements due to ill health, and transfers to alternative work due to lung cancer amongst various groups of London Transport employees. Results of pollution measurements in any garage are only applicable to the particular types of vehicle involved and to the running conditions obtaining within it, but they are of direct relevance to the health of the men employed there.



METHODS

Samples of smoke for hydrocarbon analyses were collected on weighed glass fibre filter sheets measuring 8 in. by 10 in. overall. These were supported on a wire mesh framework and air was drawn through with a vacuum cleaner motor. The air flow through the filter was measured with a miniature float-type meter mounted in the outlet. The flow, which gradually fell as the filter became laden with smoke, was about 1 cubic metre per minute. In addition small filters were used to determine the concentration of smoke (and, at Dalston, sulphur dioxide) at five points around the garage. These were of the type specified by the Department of Scientific and Industrial Research for atmospheric pollution measurements . A continuous strip recorder was used to obtain a semiquantitative record of smoke concentration over long periods; it was started at the beginning of each experiment and was left running for one week (Dalston) and two weeks (Merton) to check day-to-day variations.

Each glass fibre filter was weighed and extracted with cyclohexane in a Soxhlet apparatus for three hours, and the yellow solution so obtained was reduced to small volume and transferred to a column of alumina. The hydrocarbons were separated by elution with cyclohexane and were determined spectrophotometrically (Commins, to be published).

The two main samplers which were used to collect smoke for hydrocarbon analyses were run side by side on a separate occasion and the concentration determined from each to ensure that they were giving comparable results. These samples were combined and used to provide material for repeated determinations of 3 : 4-benzpyrene and some other hydrocarbons. The cyclohexane extract was divided into four parts and the results of repeated analyses are given in Table 1. This experiment gave only a rough estimate of the standard deviation, but it enables some assessment to be made of the significance of differences in the main experiment. The coefficients of variation are of the same order as those found in repeated determinations on general atmospheric smoke (Commins, to be published).

Nitrogen dioxide was determined colorimetrically by the method described by . Aldehydes were absorbed in sodium bisulphite solution and determined by the method of . At Merton garage two samples of air were collected in evacuated bottles and the- concentration of carbon monoxide was determined with an infra-red analyser. In addition, blood samples were taken from two subjects before and after exposure to pollution within the garage. The carbon monoxide in these samples was determined by the method of Lawther and Apthorp (1955).

RESULTS

Smoke and Hydrocarbons.-The amounts of smoke and hydrocarbons per 100 cubic metres of air sampled inside and outside each garage are shown in Tables 2 to 5.

Except where otherwise stated the figures represent single estimations. Anthracene and 1: 2-benzanthracene were detected but, as their determination was interfered with by some other compounds, results are not quoted. Phenanthrene, chrysene, coronene, and anthanthrene were also found in some samples. During periods 1, 2, and 4 on each occasion buses were moving in the garage, and the concentration of smoke was much higher inside than out. In general the differences in the concentrations of hydrocarbons inside and outside each garage were less marked.

Table 2 gives the results of the first experiment at Merton and shows that the concentrations of 1 : 2-benzpyrene, 3 : 4-benzpyrene, and 1 : 12-benzperylene were virtually the same inside and outside the garage during each of the four periods. Pyrene and fluoranthene concentrations were at times somewhat higher in the garage than outside. Since the concentration of smoke was higher inside the garage than outside, it is clear that the smoke produced by the buses contains a lower proportion of hydrocarbons than that outside. This first Merton experiment was carried out on a cold, still night and the concentration of smoke outside the garage was exceptionally high for the time of year. To assess more closely the effect of the buses the experiment was repeated in June when the general level of smoke was much lower. The concentrations of all hydrocarbons (Table 3) were very much lower than on the previous occasion, and were higher inside the garage than out during periods 1 and 2, indicating that the buses produced small amounts of hydrocarbons.

The experiments at Dalston garage were carried out in exactly the same way as those at Merton. Results from the first experiment on October 24/25 are shown in Table 4. The concentration of smoke was higher at the main sampling point inside the garage than outside at all times when buses were moving. 

As in the first Merton experiment the concentrations of 1: 2-benzpyrene, 3: 4-benzpyrene, and 1: 12-benzperylene were virtually the same inside and outside the garage, and again the concentrations of pyrene and fluoranthene were higher inside. Although a reasonably clear day had been chosen for this experiment, the concentrations of smoke and hydrocarbons outside during the first period were rather high, due to the emission of smoke from a number of nearby domestic chimneys. Hence, as at Merton, it was necessary to repeat the experiment when the emission from chimneys was expected to be at a minimum. The results of this experiment (June, 1957) are shown in Table 5; in general the concentrations of hydrocarbons were higher inside the garage than outside, indicating again the emission of small amounts by the buses.

The results obtained with the small smoke filters at various points in and around Merton garage are given in Table 6.

These measurements, which were made on a separate occasion, covered the first two periods only. They indicate the relative concentrations of smoke in and around the garage, but the absolute values are only approximate. The site (A) chosen for the main samples within the garage did in fact show the highest concentration of smoke. Next in order of magnitude came the office site (D) past which most buses run; the office door was on the same side as the exhaust pipes. At Dalston garage small filters were run concurrently with the main samplers covering each of the four periods; they also were left for a fifth period (7 a.m. to 5 p.m.). Results from the first visit are shown in Table 7. Again the site (P) chosen for the main samples during the first three periods showed the highest smoke concentration.

During the fourth period the main samples were collected at Q. It can also be seen from Table 7 that three of the garage sites showed lower concentrations of smoke than the outside sampling point (R). This suggested that an excessive amount of local pollution was being collected at the outside site. It came from nearby domestic chimneys, and this made it necessary to repeat the experiment during the summer when the amount of smoke from this source would be less. Results from the small filters on this second visit are shown in Table 8. The garage entrance (P) again showed the highest concentration of smoke in each period. On this occasion at none of the garage sites was there substantially less smoke than outside. During the day (period 5) the concentration in the dock was as high as that at the garage entrance. Sulphur dioxide concentrations were measured at each of the sites in the Dalston garage on the second visit and were well within the levels normally found in urban areas; there was no marked excess of sulphur dioxide within the garage, the highest concentration being 0-04 parts per million.

The continuous smoke sampler referred to earlier 2 12 * 2 was installed at Merton (site A, Fig. 1) at the beginning of each visit, and was left running for a period of two weeks. It was also installed at Dalston (site P, Fig. 2) at the beginning of the first visit there and was left running for one week. A smoke trace of greatly varying density was obtained with distinct "bursts" where buses had passed near during the run-in. The pattern of these "bursts" was similar on each week day with some variations at weekends. The "background" pollution was generally highest in the evening. The record showed that the level of smoke was much higher during the experiment at Merton on April 18/19 than on any of the succeeding 13 days, but that the general pattern was similar each day. There was little difference between successive days in June and the day chosen for the second experiment at Merton could be regarded as typical for the time of year. The record from Dalston showed that there was rather less pollution on the day of the first experiment there than on some of the subsequent days.

On the second visit to Dalston the continuous smoke filter was fitted with paper impregnated with thymol blue and was run through periods 1 to 4 only. A similar smoke trace was obtained, and the most intense  "bursts" during the run-in in the evening showed a pink coloration around the smoke. This indicated the presence of small quantities of acid, probably sulphuric acid. The effect was no greater than that observed at times in ordinary urban air.

The concentrations of nitrogen dioxide found in Merton and Dalston garages are shown in Table 9. Some samples were taken continuously throughout each period and others were collected instantaneously in evacuated litre bottles. Analyses from the first Merton experiment show that the nitrogen dioxide appears to follow the concentration of smoke. The results quoted from the second visit to Merton are not necessarily representative of the average concentrations during each period, since they are based on instantaneous samples only. Continuous samples Dalston 0-1 0-03 * 0-2 were taken during each of the two visits to Dalston and these followed the concentration of smoke in a similar manner. The maximum concentration of nitrogen dioxide found outside Dalston garage was 0-02 p.p.m. Samples taken in evacuated bottles a few feet from the end of the exhaust pipes of several buses at each garage contained up to 15 p.p.m. nitrogen dioxide.

Table 10 shows the concentrations of aldehydes found in Merton and Dalston garages; any ketones present would be included in these figures. Results obtained during the three periods when buses were moving in the garage were considerably higher than those obtained during period 3. Two samples taken in evacuated bottles directly from the exhausts of buses at Merton garage were found to contain 20 and 50 p.p.m. of carbon monoxide. The amount of carbon monoxide in the blood of one subject (BTC) rose from 0-038 to 0-075 volumes % between 5.30 p.m. and 12.30 a.m., whilst that in the blood of another subject (REW) fell from 0-350 to 0-075 volumes % during the same period. Neither subject was a smoker.


