大気中低級炭化水素各成分濃度の時刻変動相互関係および各成分の発生源の推定

抄録

Several series of sampling of light hydrocarbons in ambient air were made in 1970 and 1971. Air was taken in a 200ml syrings for every 30 to 60 minutes on a roof of the 5th story of the Institute of Public Health (I. P. H) building in Minato-ku, Tokyo and measured by gas chromatography.
A U-sharped trap (1.5ft x 1/in. od. stainless steel tube) filled glass beads (30/60mesh) was attached to six-port gas sampling valve on a gas chromatograph. The sampling gas in a 200ml syringe was passed through the trap which was chilled in liquid oxygen. The trap was then brought to 60-80°C by hot water and its contents simultaneously swept into the column. The chromatographic column was consisted of a 36ft x 1/8in. od. stainless steel tube packed with 10% dimethyl sulfolane coated on 40/60mesh of C-22 plus 1. 5ft x 1/8in. od. stainless steel tube packed with 10% carbowax 600 coated on 40/60mesh C-22. The dimethylsufolane column and the carbowax 600 column respectively maintained at 0°C and room temperature during analytical procedures. Dry nitrogen was used as carrier gas and its flow rate was 20ml/min. The results of the measurements are shown in the appendix.
The diurnal variations of total light hydrocabon concentrations incicate two peaks in a day and are very similar to that of the SO₂ concentrations at the Tokyo Tower (see Fig. 1), although the sources of hydrocarbon and SO₂ are apparently different. Therefore their concentrations are probably strongly affected by weather.
The percentages of each hydrocarbon in total hydrocarbons are shown in Fig. 2. The proportions of propane. isobutane and n-butane reach maximum in the midnight, but that of propylene, I-butene, and isobutene which are active in photochemical reaction are approximately constant. The standard deviations of these variation of concentrations of these hydrocarbons increase in the following order, 1-butene, isobutene <propylene<n-pentane<isopentane<2-methylpentane, 3-methylpentane<n-hexane<isobutane<n-butane<propane<acetylene.
The correlation coefficients and the slopes of regression lines were also calculated between the concentrations of two different components, and the diagram of correlation was constructed (see Table. 1 and Fig.3), It should be noticed that the correlations of isobutane-n-butane, and isopentane-n-pentane are always very significant, all the slopes of the regression lines containning the value at intersections are nearly equal (see Table. 2). These show that the main source of ambient hydrocarbons is seemed to he automobile exhaust.
To estimate the contribution of the source to ambient hydrocarbons, we measured hydrocarbon concentrations at various sources which are listed in Table. 3. It is recognized from Table 3 that the main sources of ambient propane, isobutane, n-butane, isopentane and n-pentane are the exhaust gases from “gasoline A”, “gasoline B ” and “propane” shown in Table 3, gasoline vapor, and leak of liquid propane gas. The rate of contribution of these five sources can be calculated from the values in Table 3 on several suppositions. Supposing “gasoline A”/ “gasoline B” ratio to be the same as that described in the National date in 1969, the validity of these suppositions could be tested by using isobutane concentration, and it is proved by the agreement between the calculatedand found values (see Table 4). The proportions of source strenght [of], “Propane-power autoes” to that of “gasoline-powered autoes” were calculated from eq.(12) and the diurnal variations are shown in Fig 4. It is always found that the propane-drived taxies are relatively abundant at midnight.