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Long-term variation of chemical composition of atmospheric aerosol on the Oki Islands in the Sea of Japan
Atmospheric Environment Vol. 24A, No. 6, pp 1379 1390. 1990. Printed in Great Britain.
0004 6981/90 $3.00+0.00 Pergamon Press pie
L O N G - T E R M VARIATION OF C H E M I C A L C O M P O S I T I O N OF A T M O S P H E R I C AEROSOL O N THE OKI ISLANDS IN THE SEA OF JAPAN HITOSHI MUKAI, YOSHINAR1 AMBE a n d KEIKO SHIBATA Chemistry and Physics Division,National Institute for Environmental Studies,Onogawa Yatabe, Tsukuba, Ibaraki, 305, Japan
and TATSUNORI MUKU, KAZUO TAKESHITA,TSUNEO FUKUMA,JUNICHI TAKAHASHIa n d SHINJI MIZOTA Saigo Health Center, Shimane, Minatomachi Saigo-cho, Oki, Shimane, 685, Japan (First received 23 January 1989 and in final fi)rm 31 August 1989) Chemicalcomposition in aerosols collected on the Oki Islands, which are located in the Sea of Japan, were measured for 4½years (1983-1988)and their variations were investigatedfrom the viewpointsof aerosol background level and transport of aerosols from both the mainland of Japan and the Asian Continent. Kosa, which is soil dust from the Asian deserts, strongly influenced the variations of the concentration of soil-derived components in aerosol, which showed high concentrations every spring and November. Sulfate had a good correlation with V in the variation and their concentrations increased in summer as the result of the transport of the aerosol from the mainland of Japan. Whereas high Pb concentration in winter was presumed to be attributed to the contribution of lead-enriched aerosol transported from the Asian Continent by the northwest monsoon. The differences of aerosol composition between summer and winter were seen in the ratios of Pb/Zn and Sulfate/V, which may be good indicators for the characterization of aerosol in Asian region. Long-term trends of changing of aerosol composition were also studied, and only C indicated a slight increase for 4 years. Abstract
Key word index: Regional background aerosol, chemical composition of aerosol, long-term monitoring, long-range transport, the Asian region.
I. INTRODUCTION In recent years, long-range transport (LRT) of air pollutants such as S related compounds has caused some serious environmental problems in European countries (Ottar, 1976; Wright and Gjessing, 1976; Schofield, 1976; Hauhs and Wright, 1986). It was also found that some other pollutants such as Pb and some metals (Lannefors et al., 1983; Qblad and Selin, 1986), and soot (Brosset, 1976; Rosen et al., 1981; Rosen and Novakov, 1983), were transported on a regional scale. In many cases, the observation of these pollutants at regional background sites such as Arctic (Ottar, 1981), remote mountainous sites (Reiter et al., 1984, 1986) and islands (Darzi and Winchester, 1982; Duce et al., 1983; Prospero et al., 1985) were useful not only to know the natural base line level of air pollutants but also to detect the air pollutants transported. In the Asian region, a few reports concerning LRT from the mainland of Japan have also been published (Meteorological Research Institute, 1979; Okita et al., 1986; Ito et al., 1986). Especially in winter, relatively high concentrations of pollutants were observed on islands in the western Pacific Ocean, which means the
northwest monsoon in winter transported air pollutants from Japan to the Pacific. But the data on LRT between Japan and the Asian Continent has not appeared yet except in the reports on soil dust from Asian deserts (Ishizaka, 1972; Duce et aL, 1980; Ishizaka et al., 1981; Uematsu et al., 1983). One of the aims of this study is to know the regional background level of air pollutants around the Sea of Japan and to evaluate the influences of LRT between Japan and the Asian Continent. The other aim is to study about the long-term trend of air pollution in the Asian region. For these reasons, the aerosol composition has been measured since 1983 on an island (Oki Islands) in the Sea of Japan. In this paper, we present the results of the chemical analysis of the aerosol collected monthly for over a 4-year period on this island, along with seasonal characteristics of aerosol composition. 2. EXPERIMENTAL
2.1. Samples The Oki Islands are located in the Sea of Japan (Fig. 1), about 90 km distant from mainland of Japan to the north
1379
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HITOSHI MUKAI et al. was heated (200°C) over 4-h, until black soot was decomposed. Si (as SiO2 in the filter and soil component) was removed by the treatment of 5 ml of HF (Special grade, Wako Pure Chemical Ind. Ltd. or Suprapur, Merck). Finally, this solution was evaporated to near dryness and was dissolved with 5 ml of 0.4 N HNO 3. Metal elements in this solution were analyzed by inductively coupled plasma atomic emission spectroscopy (Jarrel-Ash Plasma Atomcomp, model 975, and Seiko Ind. Inc., JY-48PVH). Water soluble compounds such as SO~2- , N O 3 , C1- and NH~ were extracted from an eighth of the filter by 10 ml of deionized water and analyzed by ion chromatography (Dionex model 10 and QIC). Carbon and N were determined with CHN analyzer (Yanaco, MT-2) by use of the sample collected on quartz fiber filter.
3. RESULTS AND DISCUSSION
3.1. Average concentrations of chemical composition of aerosol
Fig. 1. Map showing eastern Asian area and the sampiing sites on the Oki Islands, expanded at the upper part of the map.
and about 300 km distant from the edge of the Asian Continent. About 30,000 people live there, and there is no large pollution source except for two small power plants and fishing boats. The opposite side of these islands, which is Shimane or Tottori prefecture, also has no large industrial area. There are, however, some industrial areas in mainland Japan. The two nearest ones are about 200 km and 300 km from the Oki Islands to the south and to the southwest, respectively. Aerosol was collected monthly with two low volume air samplers on the mountain top (200 m a.s.1.) at Dogo on the Oki Islands (site 1). Two kinds of samples were used for the metal analysis and for C analysis, respectively. That is, a cellulose nitrate membrane filter (Advantec, A-300, 11 cm dia.) and a quartz fiber filter (2500 QAST, Pallflex Products Co.) wer~ fitted with two samplers, respectively. As these samplers have a cyclone type classifier, particles > 10 #m dia. were almost removed before sampling. Sampiing was usually done during 1 month with a flow rate of 20 f min- ~; usually, the 20th day of every month is the day for changing filters. In order to know the contribution of anthropogenic local pollution of this island, another sampler was placed on the roof of the office building at site 2, which faces the Saigo Bay; a small power plant is at this bay shore. Quartz fiber filters were heated (300°C) in a vacuum oven overnight prior to use. These filters were kept in the air conditioned room (20°C, r.h. <60%) for over 2 days, and were weighed. Then, they were sent to Saigo Health Center at Dogo by mail. After sampling, these filters were sent back to our institute and kept in the storeroom (-20°C), until analyses were made. 2.2. Analysis A quarter of the membrane filter was placed in a 100 ml Teflon beaker and digested with 5 ml of conc. HNO 3 (ELSS, Kanto Chemical Co., Inc.), 12 ml ofHzO 2 (for AAS analysis, Wako Pure Chemical Ind. Ltd.) and 5 ml of HCIO, (for poisonous metal analysis, Wako Pure Chemical Ind. Ltd.). It
T h e arithmetic m e a n c o n c e n t r a t i o n s a n d s t a n d a r d deviations of 24 aerosol chemical compositions based o n the m e a s u r e m e n t s from D e c e m b e r 1983 to M a y 1988 at site 1 are s h o w n in Table 1, including the values of some other locations. N o n o d a k e is one of the m o n i t o r i n g stations of the N a t i o n a l Air Surveillance N e t w o r k in J a p a n (Air Quality Bureau, E n v i r o n m e n t Agency, Japan) a n d one of the cleanest sites in this network. Almost all values of the Oki Islands were the same as or lower than those of Nonodake. In comparison with the values of N o r t h Alpine (Reiter et al., 1986) a n d Sweden (Lannefors et al., 1983), soil-derived elements such as Al, Fe, Ca, K, M g a n d Ti were considerably higher, because the soil c o m p o n e n t s derived from K o s a (soil dust from the Asian deserts), which come to J a p a n in every spring, raised the average c o n c e n t r a t i o n s of these soil-related elements. O n the o t h e r h a n d , some a n t h r o p o g e n i c elements such as Zn, Pb, Cu, Ni, a n d V showed c o m p a r a b l e values at three sites, despite that these sites have different geographical conditions. Sulfate c o n c e n t r a t i o n was slightly high at the Oki Islands. This m a y result from the t r a n s p o r t a t i o n of large a m o u n t of SO 2 - from the m a i n l a n d of J a p a n in s u m m e r season as s h o w n below. The equivalent ratio of NH,~ to SO 2 - was a b o u t 0.4, which means SO 2 was not neutralized completely a n d partly exists as H 2 S O 4. Since this H2SO 4 causes C l - a n d N O 3 loss (Hitchcock et al., 1980; H a r r i s o n a n d Pio, 1983) from sea salt particles or others on the filter during the sampling period of one m o n t h , C l - a n d N O ~- values in this table do not reflect real c o n c e n t r a t i o n in the a t m o s p h e r e ; their values are too low c o m p a r e d to those of o t h e r sites. F r o m rough calculation, it was found that aerosol sampled o n this island comprised soil (22%), sea salt (8%), NH,~ a n d SO42- (35%), NO~- (1%), c a r b o n (15%) a n d some metal elements (0.3%). The summ a t i o n of these c o m p o n e n t s was > 8 0 % . If organic c o m p o u n d s were added to this summation, we could explain a b o u t 9 0 % of the content of the aerosol.
Chemical composition variation of aerosol
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Table 1. Average concentrations of aerosol mass and chemical composition from December 1983 to May 1988 on the Oki Islands (site 1), including the data at other sites for comparison Components Aerosol (ttg m 3t SO ]- (/~g m - 3) C NH.~ Na NO 3 CI A1 Ee Ca K Mg Zn (ng m 3) Pb Ti Mn As Cu V Sr Ni Cd Co Sc Cr
Arithmetic mean 12.2
S.D. 4.50
3.59 1.73 0.510 0.430 0.114 0.045 0.228 0.150 0.151 0.130 0.107 14.9 12.4 12.4 5.61 3.28 1.65 1.58 1.34 0.903 0.276 0.196 0.045 <2.0
1.06 0.534 0.282 0.136 0.104 0.0936 0.174 0.102 0.105 0.0589 0.0489 3.97 4.64 9.55 2.73 1.65 0.798 0.623 0.718 0.345 0.113 0.112 0.037 (1.35)
Nonodake* 15.0
North Alpinet 1.90
0.610 0.090 0.270 0.180 0.290 0.230 40 31 26 8.3 3.1 < 10 3.1
0.725 0.039 0.747 0.062 0.086 0.056 0. I 01 0.035 10.8 11.7 1.58
Sjoangen++ 2.4
0.19 0.088 0.074 0.076 24 21 5.0 6.7 2.4 2.5
-~ 2.7 2.6 0.1 0.053 1.0
1.5 0.032 2.8
* Miyagi Pre. Japan. Arithmetic mean values in 1984, from NASN data (Air Quality Bureau, Environment Agency, Japan, 1985). ?Arithmetic mean values (198(~1984) at Wank (1780 m a.s.1.), F.R.G. (Reiter et al., 1987). ++Arithmetic mean values during 1 year (1976), Sweden (Lannefors et al., 1983). Concerning enrichment factor (E.F.), which is defined as (X/A1) ...... ~/(X/Al)crust, that of Pb was calculated to be 2943, normalized by A1 of earth crust (Taylor, 1964). Zn, As and Cd also has high values; 132, 581 and 669, respectively. These values were similar to those of North Alpine (Reiter et al., 1987), indicating that there are some contributions from anthropogenic sources to the aerosol on this island.
3.2. Trend of concentration changes for 4 years Figures 2 and 3 show the variations of concentrations of aerosol and some representative chemical composition of it. In these figures dashed lines indicate annual mean values. Averaged aerosol concentrations were almost constant for 4 years, showing the seasonal variation having the local maxima in spring and summer. These two maxima corresponded to AI and sulfate concentration peaks, respectively. The variation of AI concentration was illustrated along with the occurrences of Kosa phenomena (arrows) in Fig. 2(b). It was found that the AI concentration was strongly influenced by the Kosa phenomenon. The concentration of AI at the non-Kosa season was about 150 ng m 3, but during spring this concentration increased up to about 800 ng m - 3. This was considered to be responsible for the high average values of soil components, compared to those of other countries as mentioned above. Since the scale of the Kosa phenom-
enon changed from year to year, annual mean values also changed; for instance, in Japan we had large scale ones in 1984, 1985 and 1988. Therefore, it is difficult to evaluate the trend of changing of its concentration. Calcium was often reported to be enriched in Kosa particles (Mizohata and Mamuro, 1980). The ratio of Ca, which was corrected by the subtraction of Ca corresponding to sea salt from total Ca, to A1 is 0.65 +0.11 (S.D.) in Kosa periods (1985-1987) but 0.57 _+0.7 (S.D.) in non-Kosa periods. Therefore, on average Ca seemed to be slightly enriched compared to AI in Kosa period. But the range of this ratio was from 0.41 to 0.86, indicating the composition of Kosa particle varies with the place of origin. Sodium had a tendency to decrease in annual mean concentration (Fig. 2(c)). This was related to the decrease of contribution from soil as shown by annual change of A1, because a part of Na is derived from soil component. On the other hand, annual mean concentration of sulfate was almost constant (Fig. 3(a)). Sulfate concentration showed an increase in every summer except wet season (early July) and sometimes high concentrations were observed in spring. Since the wind from the southwest blows frequently in summertime in Japan, the increase of SO ] - concentration at this season was considered to be attributable to the transport of SO 24from the mainland of Japan. The contribution of SO 2 from sea salt was under 3% of total SO24 , so
1382
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Fig. 2. Variations of (a) aerosol, (b) A1 and (c) Na concentrations in the atmosphere for 4½ years on the Oki Islands. Dashed lines are their annual averages.
that the greater part of the SO~- was so-called excessSO 24-. Since the level of excess (non-sea-salt)-SO42- at the Pacific was reported as < 1/~gm-3 (Saitzman et al., 1986), these observed values were rather high. Carbon was the only element that had a tendency to increase. The variation pattern was complicated and there seemed to be different sources at each season. Soot particles are known as a pollutant that is transported to remote area such as the Arctic (Rosen et al., 1981), so it may be a problem also in the Asian region from the standpoint of LRT of air pollutants.
Lead, Zn and Cu showed no remarkable change in annual mean concentration for 4 years, in contrast to the Pb concentration at North Alpine which was reported to have decreased gradually in the last 10 years (Reiter et al., 1984).
3.3. Characteristics o f seasonal variations Figures 4(a), (b) and (c) show the seasonal variations patterns of the atmospheric concentrations of chemical composition; each value is averaged at each month
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for 4½.years. From these figures, it was found that these seasonal variations could be classified into the following four groups. (1) High in spring--A1, Fe, K, Ca, Ti, Mn, Sc, Sr, Co. (2) High in s u m m e r - - S O l - , NH,~, C, V, Ni, N, Cu. (3) High in winter and spring--NO 3 , CI -, Na, Mg, Cd, As, Pb. (4) Not clear--Zn.
The first group is soil component and their concentration increased in spring and November. As mentioned above, spring is a typical season of Kosa, but Kosa is also observed in November (Arao et al., 1979). Hence it was considered that peak of November was due to soil particles transported from the Asian deserts. Sulfate, V and Ni (also C) of the second group are related to oil burning. High V and Ni concentrations in summer suggested that high concentration of SO in summer did not result from the increase of conver-
1384
HITOSHIMUKAIet al. (a)
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sion rate of S O 2 t o S O ,2- but the increase of primary emission; probably SO 2- was carried by the south or southwest monsoon from the industrial area of Japan. The contribution from human activity including the power plants on this island was considered to be small, because SO,2- and other elements concentrations in aerosol collected at site 2 were similar to those of site 1, although site 2 faces the harbor where there are some buildings and fishing I~oats. This means that the variation of aerosol composition on this island was mainly affected by aerosols transported from surrounding areas. Nitrate and CI- showed the reverse pattern to SO,2- due to the reaction with H2SO 4. Nitrate and Cl- were found to exist as coarse particles in both summer and winter by the measurement of size distribution of main ions. Nitrate was considered to react with sea salt particles. Therefore, this variation is not due to the formation of NH,NO3 and NH4C1 in the cold season (Stelson et al., 1979). On the other hand, in spring a lot of soil dust containing much Ca exists in aerosol, so these CI- and NO 3- losses seemed to be hindered by the reaction with CaCO 3 with H2SO4 instead of NO 3 and CI-. Thus, these variation patterns do not show actual variations, as found from the inconsistency of variation pattern between CI and Na. As Mg came from sea salt in addition to soil, its variation pattern was similar to that of Na. The third group also contained some anthropogenic elements such as Pb and As. Especially, Pb concentration increased in winter in contrast with sulfate. Since Pb concentration, not only in the atmosphere but also in aerosol, was high in winter, a different aerosol seemed to be sampled in between summer and winter. Furthermore, it was significant that its concentration was considerably higher in spring, which is Kosa season.
Zinc was considered to have various sources and its concentration did not vary seasonally so much. 3.4. Correlations among chemical compositions In order to know the relationships between components, correlation coefficients were calculated on the basis of their concentrations in the atmosphere (Fig. 5). Soil components such as Al, Fe, Ca, Ti had good correlations (r>0.8) with other. Some scatter diagrams of soil-derived elements are illustrated in Fig. 6; circles and triangles mean winter (November-April) and summer (May-October) samples, respectively. Regression lines of these elements
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Fig. 5. Correlation matrix of aerosol components, based on the concentrations in the atmosphere. Correlation coefficients are indicated as the degree of the density of the shade.
Chemical composition variation of aerosol
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(Fe, Ca, Ti and Sc) from A1 had the intercepts of almost zero (for instance Fig. 6(a) and (b)) and their slopes (Ti/AI: 0.054, Fe/AI: 0.58) were consistent with crustal abundance (0.054 and 0.62, respectively). But the intercepts of the regression lines of K and M n from A1 were not zero (Fig. 6(c) and (d)), they were considered to get a little contribution from other anthropogenic sources in addition to soil. Whereas as Mg (and also St) had a contribution from sea salt in addition to soil, the intercepts of their regression lines were not zero either (Fig. 7(a)). If we plot the scatter diagram between A1 and soil-derived Mg, which is calculated by Equation (1), it is found that they are highly correlated and its intercept was almost zero (Fig. 7(b)), indicating that Mg had two sources; soil and sea salt. Soil Mg = total M g - 0 . 1 2 0 × sea salt Na
(1)
0.120 was ratio of Mg to Na in sea water (Weast, 1978) sea salt Na = total N a - s o i l Na soil Na = 0.348 x AI (from crustal abundance). As mentioned above, SO 2- had correlations with V, Ni, NH,~ and C, as shown in Fig. 5. From the scatter diagram of excess-SO 2- vs N H 2 (Fig. 8), it can be found that only a half of SO 2- is neutralized by N H ~ , which means at least half the residue exists as H2SO 4 or most sulfate exists as NH4HSO 4, even though gaseous N H 3 may neutralize these acids on the filter
both during and after sampling. A photograph of the aerosol, collected on the electron microscope grid covered with thin film of formval by using an electrostatic aerosol sampler, is shown in Fig. 9. Many particles have the morphology characteristic of H2SO 4 or NH~HSO4 as reported by Ferek e t a / . (1983). Therefore, it was considered that most of the H2SO 4, which is produced by the conversion from SO 2, was not neutralized by NH3, because the concentration of NH 3 was low over the ocean (Okita et al., 1986). The negative value of the correlation coefficient for C I - - S O ~ - (Fig. 5) suggested that acidic SO~ particles caused C1- loss. This CI loss by H2SO 4 particles probably occurred on the filter during the sampling period. Aerosols having a satellite ring like Fig. 9 were observed in both summer and winter, which was consistent with the result that the ratio of NH~ to S O l - was low in both summer and winter, as shown in Fig. 8. Zn, Cu, Pb, As and Cd had some correlations with each other and especially Z n - C u , Z n - P b and P b - A s were significant. Zn and Pb also indicated some correlations with soil components. But the correlation coefficients, calculated based on concentrations in aerosol instead of the atmosphere, did not show good correlations, so that their relations were considered to be insignificant.
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elements, as shown in the last section. But the seasonal characteristics were found in the relations of Pb vs Zn and excess-SO 2- vs V. Figures 10 and 11 show the scatter plots of these pairs. In both cases, winter samples (circle plots) had higher values in slopes of their regression lines. This means that Pb and SO~are concentrated to Zn and V, respectively in winter. Figure 12 shows the averaged ratios of Pb to Zn in aerosol in winter (December 1983-March 1984) at several sites of Japan in addition to the Oki Islands, which were calculated from NASN data (Air Quality Bureau, Environment Agency, Japan, 1984). These sampling sites include not only several urban areas but also rural areas such as mountainous sites. The values of many sites were under 0.67, despite that the northern city, where coal is used as a fuel for heating the home in winter, had a lower value (for instance 0.198). But that of the Oki Islands (1.13) is at least two times higher than those, indicating that the somewhat different aerosol from Japan was observed on this island in winter; the average of this ratio on the Oki Islands for 4½ years was 0.97+0.15 in winter but 0.66+0.13 in summer. Oblad and Selin (1986) pointed out that the ratio of Pb to Br in aerosol at a background site in Sweden changed with the air mass trajectories. In view of the main wind direction in winter at the Oki Islands, this high value of the ratio of Pb to Zn may be due to the transport of Pb-concentrated aerosol from the Asian Continent. On the Oki Islands, wind direction apparently changes with season because of the monsoon. As the major wind direction is not so influenced by local winds on a small island, the surface wind direction observed on this island is not different basically from the wind direction at high altitudes such as the 850 mb level. In Fig. 13, surface wind directions are classified into the wind from the main land of Japan (NE-E-S-WSW) and from the direction of the Asian Continent (W-NW-N), and their frequencies are plotted for each month. Based on these data, 60-75% of wind directions in winter are found to be from the direction of the Asian Continent, whereas in summer the wind from the mainland of Japan is dominant. Since leaded gasoline is still in use in Asian coun, tries, a high concentration of Pb in the air has often been reported. Rho (1984) reviewed the pollution in Korea and introduced Pb concentrations to be 1240-3180 ngm -3 in 1977-1978. The ratio of Pb to Zn was also calculated to be 3.9-5.5 from this data. This high ratio is probably due to the enrichment of Pb by the large contribution from leaded gasoline. However, as the production of unleaded gasoline have been started since mid-1987 in Korea (Kim and Cho, 1986), atmospheric Pb concentration is expected to decrease gradually in the future. In China, leaded gasoline was also used, but Dod et al. (1986) reported that most atmospheric Ph (143 531 ngm 3) in China was derived from coal combustion. The ratio of Pb to Zn was 0.424).82, which were slightly high values compared to those of typical cities in Japan (0.204).67)
Chemical composition variation of aerosol
1387
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Fig. 10. Scatter diagram of Pb concentration vs Zn concentration in the atmosphere on the Oki Islands. Winter samples (November-April), indicated by circle plots, are showing the different relation from that of summer samples (May-October), which are indicated by triangle plots. Correlation coefficients for winter and summer samples were 0.829 and 0.873, respectively. Average lead concentrations in winter and summer were 15.0 and 9.5 ngm -3, respectively.
Fig. 11. Scatter diagram of excess-SO42 vs V-sV(total V - s o i l V), which means non-soil-V. Group of winter (November-April) samples (circles) and summer (May-October) samples (triangles) had somewhat different slopes each other. Correlation coefficients for two groups were 0.534 and 0.623, respectively. Average concentrations of excess-SO]- in summer and winter were 3.66 and 3.36/~gm -3, respectively; those of V-sV were 1.57 and 0.96 ngm -3.
(Fig. 12). C o n t r a r y to those, atmospheric Pb concent r a t i o n in J a p a n was reported to be 28-170 n g m - 3 in 1984 (Air Quality Bureau, E n v i r o n m e n t Agency, Japan, 1985). Leaded gasoline is rarely used in J a p a n a n d its p r o d u c t i o n h a s been stopped since 1987. This ratio
on the Oki Islands in s u m m e r decreased to a r o u n d 0.5, which is consistent with the Japanese value. Thus, the ratio of P b to Z n m a y be a good indicator of t r a n s p o r t of aerosol from the Asian Continent,
AE(A) 24:6-0
1388
HITOSHIMUKAI et al.
0.19~ ~/ MeanPb/7.nRatio / JO 662~ ~, (1983'De¢~1984'Ma~0.3281 0"4054'
~., ~'~
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,~0.349
- s,
,
~Q~ 0.495 ~(Dec.1984-Mar.1985) Fig. 12. Pb/Zn ratios in aerosols in winter at several sites in Japan. These values are calculated from the date of National Air Surveillance Network (Air Quality Bureau, Environment Agency,Japan, 1984, 1985).
100
,
,
,
,
,
,
+
,
,
,
o 50 g
u.P i
i
i
1
i
i
Month Fig. 13. Frequencies of the wind directions observed on the Oki Islands for 10 years. The wind directions are classified into the wind (-O-) from the main land of Japan (from NE via E and S to WSW) and (-O-) from the direction of the Asian Continent (from W via NW to N). These data are calculated from the table by The Japan Meteorological Agency (1977).
despite further detailed studies being needed. Of course, since the Pb concentration in the atmosphere was higher in winter than that in summer, its concentration itself is also considered to be an indicator. But absolute concentrations of elements in the atmosphere vary with meteorological condition, so that the ratios between elements are better indicators than such concentrations. The similar situation as above were seen in the relation between V and SO 2-. As in Japan most SO 2 is derived from oil burning, SO 2- and V have some positive correlation. By the data of Mamuro and
Mizohata (1978), the ratio of SO¢2- to non-soil-V in aerosol was 830 on average with the range (530-1150) in Japan. Whereas in the countries where coal is used as a main fuel, the ratio of SO 2- to V may be smaller than that in Japan, because V is not so enriched in coal. However, the relative SOJ- concentration increases with time by the conversion of gaseous SO 2 and the ratio of SO 2- to V also increases with time. Therefore, it is not possible to compare the ratio in Japan to those in other countries directly. For instance, Dod et al. (1986) showed S/V ratio in Beijing (China) and the ratios of SO 2- to non-soil-V were calculated to be 220-590, which are somewhat small values in comparison with the value in Japan contrary to the above assumption. But, when the molar ratio of particulate S (SO 2 ) to gaseous S (SO2) in Beijing (about 0.1) is taken into consideration, these ratios (220-590) in Beijing are considered to increase beyond the ratio in Japan (830) if enough time goes by, because the ratio of particulate S to gaseous S in Japan is about 0.3 (Matsuda and Mamuro, 1978). In the interior of Japan, the ratio in aerosols, which are retained for a long time in the air, seems to be high. By the data measured on the Ogasawara Islands (Yoshizumi and Asakuno, 1986), which are 1000 km from the mainland of Japan, the ratio of excess-SO 2- to V was about 2500 in winter. As shown in Fig. 11, the ratio of excess-SO 2- to non-soil-V (total V - s o i l V; soil V=0.00148xA1 (Mizohata and Mamuro, 1980)changed seasonally on the Oki Islands. The ratio was 3740+ 1120 in winter and 2420 + 720 in summer on average. Although it was difficult to compare the absolute values of ratios to those at other sites such as Japanese cities, Beijing, from the above reasons, the good correlation with the variation of Pb/Zn ratio, which is illustrated in Fig. 14, suggested that this seasonal difference also indicated the difference of the origin of aerosol between summer and winter; probably indicating the difference of source of SO 2- in the atmosphere or the transported distance of SO ] - . In addition, Pb/V and Pb/SO 2- ratios may also be good indicators showing the seasonal difference of aerosol composition, because the proportions of the emissions of such fuel-related components are different for each country. However, as for the values of Pb/Zn and S O l - / V , since sampling periods used in this study were too long to clarify the relations between the variations of these ratios and meteorological conditions, further studies based on a shorter sampling period will be needed for confirming the above explanations.
4.
CONCLUSIONS
Over 4 years of measurements of aerosol composition on the Oki Islands in the Sea of Japan gave much significant information on regional background levels of aerosol and the transport of aerosol around the Sea
Chemical composition variation of aerosol
1389
1O000
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Ex-S04
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0
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1988
Fig. 14. Variations of Pb/Zn ratio and excess-SO] / ( V - soil V). They are showing the similar variation pattern; they are high in winter (December-February) and low in summer. of Japan. The trends of changes of elemental concentrations for this sampling period were also studied, but there are no c o m p o n e n t s which indicated remarkable changes in a n n u a l m e a n concentrations. Only C showed a slight increase. Kosa, soil dust from the Asian deserts, influe~lced the c o n c e n t r a t i o n s of soil c o m p o n e n t s ih aerosol in spring and increased the concentration levels of soil elements by up to 5 times as much as those of nonKosa seasons. Therefore, a n n u a l average concentrations of soil-related elements were also relatively high c o m p a r e d to other countries such as Sweden. Sulfate c o n c e n t r a t i o n s were rather high c o m p a r e d to other b a c k g r o u n d sites. Especially, high concentrations of b o t h SO42- and V in s u m m e r suggested that SO42 - was t r a n s p o r t e d from m a i n l a n d Japan. In winter, V c o n c e n t r a t i o n s was lower, however, the S O l c o n c e n t r a t i o n did not decrease so much, so the ratio of S O ] - to V showed different values between s u m m e r and winter. F r o m the electron microscopic observation of aerosol, most particles containing S O l - were found to exist as H 2 S O 4 mists. Correlations a m o n g elements were studied and such information on their origins (soil, sea salt, oil b u r n i n g a n d so on) of these elements was obtained. Particularly, P b and Z n showed good correlation in each season. The P b / Z n ratio increased in winter a n d its value was different from those of typical Japanese cities. In view of the use of leaded gasoline in Asian countries, the high P b / Z n ratio and the high concentration of P b in winter were presumed to be due to the t r a n s p o r t of aerosol, in which Pb was concentrated, from the Asian Continent. In addition, SO~ / V ratio was found to suggest the seasonal differences of origins of aerosols.
Acknowledgements We are very grateful to members of Saigo Health Center and NTT (Saigo) for their assistance in field work. The helpful suggestions of Dr Y. Yokouchi, Dr T. Fujii, Dr M. Nishikawa and Dr A. Tanaka are gratefully acknowledged.
REFERENCES
Air Quality Bureau, Environment Agency, Japan (1984) Ippan kankyou taiki sokuteikyoku sokutei kekka houkoku, 1983 (annual report on the results of measurements of air pollutants in Japan in 19837, pp. 2274-2280. Air Quality Bureau, Environment Agency, Japan (1985) lppan kankyou taiki sokuteikyoku sokutei kekka houkoku, 1984 (annual report on the results of measurements of air pollutants in Japan in 1984), pp. 2298 2315. Arao K., Makino Y. and Nagaki Y. (19791 Some statistical aspects of yellow sand. Sci. Bull. Fac. Educ., Nagasaki Univ. 30, 65 74. Brosset C. (1976) Airborne particles: black and white episodes. Ambio 5, 157 163. Darzi M. and Winchester J. W. (1982) Aerosol characteristics at Mauna Loa observatory, Hawaii, After east Asian dust storm episodes. J. 9eophys. Res. 87, 1251 1258. Dod R. L., Giauque R. D. and Novakov T. (1986) Sulfate and carbonaceous aerosols in Beijing, China. Atmospheric Environment 20, 2271 2275. Duce R. A., Unni C. K. and Ray B. J. (1980) Long-range atmospheric transport of soil dust from Asia to the tropical North Pacific: temporal variability. Science 209, 1522 1524. Duce R. A., Arimoto R., Ray B. J., Unni C. K. and Harder P. J. (1983) Atmospheric trace elements at Enewetak Atoll: 1, concentrations, sources, and temporal variability. J..qeophys. Res. 88, 5321 5342. Ferek R., Lazrus A. L. and Winchester J. W. (1983) Electron microscopy of acidic aerosols collected over the northeastern United States. Atmospheric Environment 17, 1545-1561. Harrison R. M. and Pio C. A. (1983) Size-differentiated composition of inorganic atmospheric aerosols of both marine and polluted continental origin. Atmospheric Environment 17, 1733 1738. Hauhs M. and Wright R. F. (1986) Regional pattern of acid deposition and forest decline along a cross-section through Europe. Water, Air Soil Pollut. 31,463~474. Hitchcock D. R., Spiller L. L. and Wilson W. E. (1980) Sulfuric acid aerosols and HCI release in coastal atmosphere. Evidence of rapid formation of sulfuric acid particulates. Atmospheric Environment 14, 165 182. Ito T., Okita T., Ikegami M. and Kanazawa I. (1986) The characterization and distribution of aerosol and gaseous species in the winter monsoon over the western Pacific Ocean. II The residence time of aerosols and SO z in the long-range transport over the ocean. ,I. atmos. Chem. 4, 401M.I 1.
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Ishizaka Y. (1972) On materials of solid particles contained in snow and rain water: part 1. J. Met. Soc. Japan. 50, 362-375. Ishizaka Y, Ono A. and Kadowaki S. (1981) Size distribution and mineral composition of yellow sand in the air over Japan and its main origins (in Japanese). Tenki 28, 651-665. Kim Y.-K. and Cho K.-R. (1986) The motor vehicle emissions control program in Korea. Proceedings of the Second Joint Conference of Air Pollution Studies in Asian Areas (Japan Society of Air Pollution), pp. 100 110. Lannefors H., Hansson H.-C. and Granat L. (1983) Background aerosol composition in southern Sweden fourteen micro and macro constituents measured in seven particle size intervals at one site during one year. Atmospheric Environment 17, 87-101. Mamuro T. and Mizohata A. (1978) Multielement analyses of airborne particulates over various areas in Japan (I) (in Japanese). J. Japan Soc, Air Pollut. 13, 357-364. Matsuda Y. and Mamuro T. (1978) Simultaneous analysis of gaseous and particulate sulfur in the atmosphere by X-ray fluorescence spectrometry (II) (in Japanese). J. Japan Soc. Air Pollut. 13, 76 83. Meteorological Research Institute, Japan (1978) Development of monitoring techniques for global background air pollution. Technical Reports of the Meteorological Research Institute 1, pp. 1-177. Mizohata A. and Mamuro T. (1980) Chemical elemental balances and identification of air pollution sources in Sakai, Osaka (I) (in Japanese). J. Japan Soc. Air Pollut. 15, 198-206. Okita T., Okuda M., Murano K., Itoh T., Kanazawa I., Hirota M., Hara H., Hashimoto Y., Tsunogai S., Ohta S. and Ikebe Y. (1986) The characterization and distribution of aerosol and gaseous species in the winter monsoon over the western Pacific Ocean: I--Measurements taken on islands and on board a ferry boat. J. atmos. Chem. 4, 343-358. Oblad M. and Selin E. (1986) Measurements of elemental composition in background aerosol on the west coast of Sweden. Atmospheric Environment 20, 1419-1432. Ottar B. (1976) Monitoring long-range transport of air pollutants: the OECD study. Ambio 5, 203-206. Ottar B. (1981) The transfer of airborne pollutants to the Arctic region. Atmospheric Environment 15, 1439-1445. Prospero J. M., Savoie D. L. and Nees R. T. (1985) Particulate sulfate and nitrate in the boundary layer over the North Pacific Ocean. J. 9eophys. Res. 90, 10,586-10,596. Rho C.-S. (1984) Chemical pollution in Korea: An experience
of the developing countries. Studies in Environmental Chemistry for Protection of the Environment (edited by Pawlouski: L., Verdier A. J. and Lacy W. J.), 23, pp. 65-76. Elsevier Science, Amsterdam. Reiter R., P6tzl K. and Sladkovic R. (1984) Determination of the concentration of chemical main and trace elements (chemical matrix) in the aerosol from 1972 to 1982 at a North-Alpine Pure Air Mountain Station at 1780 m a.s.l. Part I: methods of measurement, total concentrations, families of elements, annual variations, trend analysis. Arch. Meteor. Geophys. Bioclimatol. B 34, 215-241. Reiter R., Sladkovic R. and P6tzl K. (1987) Marked changes in the aerosol chemical matrix recently observed at 1780 m a.s.1. (BAPMoN Mountain Station) and results of first comparisons with samples obtained simultaneously at 740 m a.s.1. Met. Atmos. Phys. 36, 83-88. Rosen H., Novakov T. and Bodhaine B. A. (1981) Soot in the Arctic. Atmospheric Environment 15, 1371-1374. Rosen H. and Novakov T. (1983) Combustion-generated carbon particles in the Arctic atmosphere. Nature 306, 768-770. Saltzman E. S., Savoie D. L., Prospero J. M. and Zika R. G. (1986) Methanesulfonic acid and non-sea-salt sulfate in Pacific air: regional and seasonal variations. J. atmos. Chem.4, 227-240. Schofield C. L. (1976) Acid precipitation: effects on fish. Ambio 5, 228-230. Stelson A., Friedlander S. K. and Seinfeld J. H. (1979) A note on the equilibrium relationship between ammonia, nitric acid and particulate ammonium nitrate. Atmospheric Environment 13, 369-371. Taylor S. R. (1964) Abundance of chemical elements in the continental crust: a new table. Geochim. Cosmochim. Acta 28, 1273-1285. The Japan Meteorological Agency (1977) Frequency table for wind direction and speed (1967-1976). Technical Data Series 42, pp. 171-172. Uematsu M., Duce R. A., Prospero J. M., Chen L., Merrill J. T. and McDonald R. L. (1983) Transport of mineral aerosol from Asia over the North Pacific Ocean. J. geophys. Res. 88, 5343-5352. Weast R. C. (1978) Handbook of Chemistry and Physics, 59th edition (1978-1979). p. F-203. CRC Press, Florida. Wright R. F. and Gjessing E. G. (1976) Acid precipitation: changes in the chemical composition of lakes. Ambio 5, 219-223. Yoshizumi K. and Asakuno K. (1986) Characterization of atmospheric aerosols in Chichi of the Ogasawara (Bonin) Islands. Atmospheric Environment 20, 151-155.
0004 6981/90 $3.00+0.00 Pergamon Press pie
L O N G - T E R M VARIATION OF C H E M I C A L C O M P O S I T I O N OF A T M O S P H E R I C AEROSOL O N THE OKI ISLANDS IN THE SEA OF JAPAN HITOSHI MUKAI, YOSHINAR1 AMBE a n d KEIKO SHIBATA Chemistry and Physics Division,National Institute for Environmental Studies,Onogawa Yatabe, Tsukuba, Ibaraki, 305, Japan
and TATSUNORI MUKU, KAZUO TAKESHITA,TSUNEO FUKUMA,JUNICHI TAKAHASHIa n d SHINJI MIZOTA Saigo Health Center, Shimane, Minatomachi Saigo-cho, Oki, Shimane, 685, Japan (First received 23 January 1989 and in final fi)rm 31 August 1989) Chemicalcomposition in aerosols collected on the Oki Islands, which are located in the Sea of Japan, were measured for 4½years (1983-1988)and their variations were investigatedfrom the viewpointsof aerosol background level and transport of aerosols from both the mainland of Japan and the Asian Continent. Kosa, which is soil dust from the Asian deserts, strongly influenced the variations of the concentration of soil-derived components in aerosol, which showed high concentrations every spring and November. Sulfate had a good correlation with V in the variation and their concentrations increased in summer as the result of the transport of the aerosol from the mainland of Japan. Whereas high Pb concentration in winter was presumed to be attributed to the contribution of lead-enriched aerosol transported from the Asian Continent by the northwest monsoon. The differences of aerosol composition between summer and winter were seen in the ratios of Pb/Zn and Sulfate/V, which may be good indicators for the characterization of aerosol in Asian region. Long-term trends of changing of aerosol composition were also studied, and only C indicated a slight increase for 4 years. Abstract
Key word index: Regional background aerosol, chemical composition of aerosol, long-term monitoring, long-range transport, the Asian region.
I. INTRODUCTION In recent years, long-range transport (LRT) of air pollutants such as S related compounds has caused some serious environmental problems in European countries (Ottar, 1976; Wright and Gjessing, 1976; Schofield, 1976; Hauhs and Wright, 1986). It was also found that some other pollutants such as Pb and some metals (Lannefors et al., 1983; Qblad and Selin, 1986), and soot (Brosset, 1976; Rosen et al., 1981; Rosen and Novakov, 1983), were transported on a regional scale. In many cases, the observation of these pollutants at regional background sites such as Arctic (Ottar, 1981), remote mountainous sites (Reiter et al., 1984, 1986) and islands (Darzi and Winchester, 1982; Duce et al., 1983; Prospero et al., 1985) were useful not only to know the natural base line level of air pollutants but also to detect the air pollutants transported. In the Asian region, a few reports concerning LRT from the mainland of Japan have also been published (Meteorological Research Institute, 1979; Okita et al., 1986; Ito et al., 1986). Especially in winter, relatively high concentrations of pollutants were observed on islands in the western Pacific Ocean, which means the
northwest monsoon in winter transported air pollutants from Japan to the Pacific. But the data on LRT between Japan and the Asian Continent has not appeared yet except in the reports on soil dust from Asian deserts (Ishizaka, 1972; Duce et aL, 1980; Ishizaka et al., 1981; Uematsu et al., 1983). One of the aims of this study is to know the regional background level of air pollutants around the Sea of Japan and to evaluate the influences of LRT between Japan and the Asian Continent. The other aim is to study about the long-term trend of air pollution in the Asian region. For these reasons, the aerosol composition has been measured since 1983 on an island (Oki Islands) in the Sea of Japan. In this paper, we present the results of the chemical analysis of the aerosol collected monthly for over a 4-year period on this island, along with seasonal characteristics of aerosol composition. 2. EXPERIMENTAL
2.1. Samples The Oki Islands are located in the Sea of Japan (Fig. 1), about 90 km distant from mainland of Japan to the north
1379
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HITOSHI MUKAI et al. was heated (200°C) over 4-h, until black soot was decomposed. Si (as SiO2 in the filter and soil component) was removed by the treatment of 5 ml of HF (Special grade, Wako Pure Chemical Ind. Ltd. or Suprapur, Merck). Finally, this solution was evaporated to near dryness and was dissolved with 5 ml of 0.4 N HNO 3. Metal elements in this solution were analyzed by inductively coupled plasma atomic emission spectroscopy (Jarrel-Ash Plasma Atomcomp, model 975, and Seiko Ind. Inc., JY-48PVH). Water soluble compounds such as SO~2- , N O 3 , C1- and NH~ were extracted from an eighth of the filter by 10 ml of deionized water and analyzed by ion chromatography (Dionex model 10 and QIC). Carbon and N were determined with CHN analyzer (Yanaco, MT-2) by use of the sample collected on quartz fiber filter.
3. RESULTS AND DISCUSSION
3.1. Average concentrations of chemical composition of aerosol
Fig. 1. Map showing eastern Asian area and the sampiing sites on the Oki Islands, expanded at the upper part of the map.
and about 300 km distant from the edge of the Asian Continent. About 30,000 people live there, and there is no large pollution source except for two small power plants and fishing boats. The opposite side of these islands, which is Shimane or Tottori prefecture, also has no large industrial area. There are, however, some industrial areas in mainland Japan. The two nearest ones are about 200 km and 300 km from the Oki Islands to the south and to the southwest, respectively. Aerosol was collected monthly with two low volume air samplers on the mountain top (200 m a.s.1.) at Dogo on the Oki Islands (site 1). Two kinds of samples were used for the metal analysis and for C analysis, respectively. That is, a cellulose nitrate membrane filter (Advantec, A-300, 11 cm dia.) and a quartz fiber filter (2500 QAST, Pallflex Products Co.) wer~ fitted with two samplers, respectively. As these samplers have a cyclone type classifier, particles > 10 #m dia. were almost removed before sampling. Sampiing was usually done during 1 month with a flow rate of 20 f min- ~; usually, the 20th day of every month is the day for changing filters. In order to know the contribution of anthropogenic local pollution of this island, another sampler was placed on the roof of the office building at site 2, which faces the Saigo Bay; a small power plant is at this bay shore. Quartz fiber filters were heated (300°C) in a vacuum oven overnight prior to use. These filters were kept in the air conditioned room (20°C, r.h. <60%) for over 2 days, and were weighed. Then, they were sent to Saigo Health Center at Dogo by mail. After sampling, these filters were sent back to our institute and kept in the storeroom (-20°C), until analyses were made. 2.2. Analysis A quarter of the membrane filter was placed in a 100 ml Teflon beaker and digested with 5 ml of conc. HNO 3 (ELSS, Kanto Chemical Co., Inc.), 12 ml ofHzO 2 (for AAS analysis, Wako Pure Chemical Ind. Ltd.) and 5 ml of HCIO, (for poisonous metal analysis, Wako Pure Chemical Ind. Ltd.). It
T h e arithmetic m e a n c o n c e n t r a t i o n s a n d s t a n d a r d deviations of 24 aerosol chemical compositions based o n the m e a s u r e m e n t s from D e c e m b e r 1983 to M a y 1988 at site 1 are s h o w n in Table 1, including the values of some other locations. N o n o d a k e is one of the m o n i t o r i n g stations of the N a t i o n a l Air Surveillance N e t w o r k in J a p a n (Air Quality Bureau, E n v i r o n m e n t Agency, Japan) a n d one of the cleanest sites in this network. Almost all values of the Oki Islands were the same as or lower than those of Nonodake. In comparison with the values of N o r t h Alpine (Reiter et al., 1986) a n d Sweden (Lannefors et al., 1983), soil-derived elements such as Al, Fe, Ca, K, M g a n d Ti were considerably higher, because the soil c o m p o n e n t s derived from K o s a (soil dust from the Asian deserts), which come to J a p a n in every spring, raised the average c o n c e n t r a t i o n s of these soil-related elements. O n the o t h e r h a n d , some a n t h r o p o g e n i c elements such as Zn, Pb, Cu, Ni, a n d V showed c o m p a r a b l e values at three sites, despite that these sites have different geographical conditions. Sulfate c o n c e n t r a t i o n was slightly high at the Oki Islands. This m a y result from the t r a n s p o r t a t i o n of large a m o u n t of SO 2 - from the m a i n l a n d of J a p a n in s u m m e r season as s h o w n below. The equivalent ratio of NH,~ to SO 2 - was a b o u t 0.4, which means SO 2 was not neutralized completely a n d partly exists as H 2 S O 4. Since this H2SO 4 causes C l - a n d N O 3 loss (Hitchcock et al., 1980; H a r r i s o n a n d Pio, 1983) from sea salt particles or others on the filter during the sampling period of one m o n t h , C l - a n d N O ~- values in this table do not reflect real c o n c e n t r a t i o n in the a t m o s p h e r e ; their values are too low c o m p a r e d to those of o t h e r sites. F r o m rough calculation, it was found that aerosol sampled o n this island comprised soil (22%), sea salt (8%), NH,~ a n d SO42- (35%), NO~- (1%), c a r b o n (15%) a n d some metal elements (0.3%). The summ a t i o n of these c o m p o n e n t s was > 8 0 % . If organic c o m p o u n d s were added to this summation, we could explain a b o u t 9 0 % of the content of the aerosol.
Chemical composition variation of aerosol
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Table 1. Average concentrations of aerosol mass and chemical composition from December 1983 to May 1988 on the Oki Islands (site 1), including the data at other sites for comparison Components Aerosol (ttg m 3t SO ]- (/~g m - 3) C NH.~ Na NO 3 CI A1 Ee Ca K Mg Zn (ng m 3) Pb Ti Mn As Cu V Sr Ni Cd Co Sc Cr
Arithmetic mean 12.2
S.D. 4.50
3.59 1.73 0.510 0.430 0.114 0.045 0.228 0.150 0.151 0.130 0.107 14.9 12.4 12.4 5.61 3.28 1.65 1.58 1.34 0.903 0.276 0.196 0.045 <2.0
1.06 0.534 0.282 0.136 0.104 0.0936 0.174 0.102 0.105 0.0589 0.0489 3.97 4.64 9.55 2.73 1.65 0.798 0.623 0.718 0.345 0.113 0.112 0.037 (1.35)
Nonodake* 15.0
North Alpinet 1.90
0.610 0.090 0.270 0.180 0.290 0.230 40 31 26 8.3 3.1 < 10 3.1
0.725 0.039 0.747 0.062 0.086 0.056 0. I 01 0.035 10.8 11.7 1.58
Sjoangen++ 2.4
0.19 0.088 0.074 0.076 24 21 5.0 6.7 2.4 2.5
-~ 2.7 2.6 0.1 0.053 1.0
1.5 0.032 2.8
* Miyagi Pre. Japan. Arithmetic mean values in 1984, from NASN data (Air Quality Bureau, Environment Agency, Japan, 1985). ?Arithmetic mean values (198(~1984) at Wank (1780 m a.s.1.), F.R.G. (Reiter et al., 1987). ++Arithmetic mean values during 1 year (1976), Sweden (Lannefors et al., 1983). Concerning enrichment factor (E.F.), which is defined as (X/A1) ...... ~/(X/Al)crust, that of Pb was calculated to be 2943, normalized by A1 of earth crust (Taylor, 1964). Zn, As and Cd also has high values; 132, 581 and 669, respectively. These values were similar to those of North Alpine (Reiter et al., 1987), indicating that there are some contributions from anthropogenic sources to the aerosol on this island.
3.2. Trend of concentration changes for 4 years Figures 2 and 3 show the variations of concentrations of aerosol and some representative chemical composition of it. In these figures dashed lines indicate annual mean values. Averaged aerosol concentrations were almost constant for 4 years, showing the seasonal variation having the local maxima in spring and summer. These two maxima corresponded to AI and sulfate concentration peaks, respectively. The variation of AI concentration was illustrated along with the occurrences of Kosa phenomena (arrows) in Fig. 2(b). It was found that the AI concentration was strongly influenced by the Kosa phenomenon. The concentration of AI at the non-Kosa season was about 150 ng m 3, but during spring this concentration increased up to about 800 ng m - 3. This was considered to be responsible for the high average values of soil components, compared to those of other countries as mentioned above. Since the scale of the Kosa phenom-
enon changed from year to year, annual mean values also changed; for instance, in Japan we had large scale ones in 1984, 1985 and 1988. Therefore, it is difficult to evaluate the trend of changing of its concentration. Calcium was often reported to be enriched in Kosa particles (Mizohata and Mamuro, 1980). The ratio of Ca, which was corrected by the subtraction of Ca corresponding to sea salt from total Ca, to A1 is 0.65 +0.11 (S.D.) in Kosa periods (1985-1987) but 0.57 _+0.7 (S.D.) in non-Kosa periods. Therefore, on average Ca seemed to be slightly enriched compared to AI in Kosa period. But the range of this ratio was from 0.41 to 0.86, indicating the composition of Kosa particle varies with the place of origin. Sodium had a tendency to decrease in annual mean concentration (Fig. 2(c)). This was related to the decrease of contribution from soil as shown by annual change of A1, because a part of Na is derived from soil component. On the other hand, annual mean concentration of sulfate was almost constant (Fig. 3(a)). Sulfate concentration showed an increase in every summer except wet season (early July) and sometimes high concentrations were observed in spring. Since the wind from the southwest blows frequently in summertime in Japan, the increase of SO ] - concentration at this season was considered to be attributable to the transport of SO 24from the mainland of Japan. The contribution of SO 2 from sea salt was under 3% of total SO24 , so
1382
HITOSHI MUKAIet al.
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1985
1986
1982
1988
Fig. 2. Variations of (a) aerosol, (b) A1 and (c) Na concentrations in the atmosphere for 4½ years on the Oki Islands. Dashed lines are their annual averages.
that the greater part of the SO~- was so-called excessSO 24-. Since the level of excess (non-sea-salt)-SO42- at the Pacific was reported as < 1/~gm-3 (Saitzman et al., 1986), these observed values were rather high. Carbon was the only element that had a tendency to increase. The variation pattern was complicated and there seemed to be different sources at each season. Soot particles are known as a pollutant that is transported to remote area such as the Arctic (Rosen et al., 1981), so it may be a problem also in the Asian region from the standpoint of LRT of air pollutants.
Lead, Zn and Cu showed no remarkable change in annual mean concentration for 4 years, in contrast to the Pb concentration at North Alpine which was reported to have decreased gradually in the last 10 years (Reiter et al., 1984).
3.3. Characteristics o f seasonal variations Figures 4(a), (b) and (c) show the seasonal variations patterns of the atmospheric concentrations of chemical composition; each value is averaged at each month
Chemical composition variation of aerosol
1383
a)
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1987
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Fig. 3. Variations of(a) sulfate, (b) carbon and (c) Pb concentrations in the atmosphere for 4½ years on the Oki Islands. Dashed lines are their annual averages.
for 4½.years. From these figures, it was found that these seasonal variations could be classified into the following four groups. (1) High in spring--A1, Fe, K, Ca, Ti, Mn, Sc, Sr, Co. (2) High in s u m m e r - - S O l - , NH,~, C, V, Ni, N, Cu. (3) High in winter and spring--NO 3 , CI -, Na, Mg, Cd, As, Pb. (4) Not clear--Zn.
The first group is soil component and their concentration increased in spring and November. As mentioned above, spring is a typical season of Kosa, but Kosa is also observed in November (Arao et al., 1979). Hence it was considered that peak of November was due to soil particles transported from the Asian deserts. Sulfate, V and Ni (also C) of the second group are related to oil burning. High V and Ni concentrations in summer suggested that high concentration of SO in summer did not result from the increase of conver-
1384
HITOSHIMUKAIet al. (a)
(b)
20
(c)
N0 3
SO, At
Ct NHz
~ .c
ve ~
C
KI
eE o o CG
Mg,
V
O c '~
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Ti
As Cu
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Zn Sc
I F M
A M d
J
A
I I I S O N D
I
I F
i M
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Month
I M
I d
I d
I A
i I I S O N D
Month
I
I L I I I I I I I I , F M A M d d A S O N D
Month
Fig. 4. Seasonal variation patterns of the concentrations of various components. Each value is averaged at each individual month (December 1983-May 1988).
sion rate of S O 2 t o S O ,2- but the increase of primary emission; probably SO 2- was carried by the south or southwest monsoon from the industrial area of Japan. The contribution from human activity including the power plants on this island was considered to be small, because SO,2- and other elements concentrations in aerosol collected at site 2 were similar to those of site 1, although site 2 faces the harbor where there are some buildings and fishing I~oats. This means that the variation of aerosol composition on this island was mainly affected by aerosols transported from surrounding areas. Nitrate and CI- showed the reverse pattern to SO,2- due to the reaction with H2SO 4. Nitrate and Cl- were found to exist as coarse particles in both summer and winter by the measurement of size distribution of main ions. Nitrate was considered to react with sea salt particles. Therefore, this variation is not due to the formation of NH,NO3 and NH4C1 in the cold season (Stelson et al., 1979). On the other hand, in spring a lot of soil dust containing much Ca exists in aerosol, so these CI- and NO 3- losses seemed to be hindered by the reaction with CaCO 3 with H2SO4 instead of NO 3 and CI-. Thus, these variation patterns do not show actual variations, as found from the inconsistency of variation pattern between CI and Na. As Mg came from sea salt in addition to soil, its variation pattern was similar to that of Na. The third group also contained some anthropogenic elements such as Pb and As. Especially, Pb concentration increased in winter in contrast with sulfate. Since Pb concentration, not only in the atmosphere but also in aerosol, was high in winter, a different aerosol seemed to be sampled in between summer and winter. Furthermore, it was significant that its concentration was considerably higher in spring, which is Kosa season.
Zinc was considered to have various sources and its concentration did not vary seasonally so much. 3.4. Correlations among chemical compositions In order to know the relationships between components, correlation coefficients were calculated on the basis of their concentrations in the atmosphere (Fig. 5). Soil components such as Al, Fe, Ca, Ti had good correlations (r>0.8) with other. Some scatter diagrams of soil-derived elements are illustrated in Fig. 6; circles and triangles mean winter (November-April) and summer (May-October) samples, respectively. Regression lines of these elements
05
Z
Fig. 5. Correlation matrix of aerosol components, based on the concentrations in the atmosphere. Correlation coefficients are indicated as the degree of the density of the shade.
Chemical composition variation of aerosol
->/..
(a)
B 400
AI
(c)
(b)
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1385
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900
20
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.941
[ng/m 3 ]
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e)
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Fig. 6. Scatter diagrams of(a) Ti, (b) Fe, (c) K and (d) Mn vs AI. Triangle plots mean samples collected in summer (May-October) and circle plots mean samples collected in winter (November April). In these figures the equations of regression line and correlation coefficient (R) are also shown.
(Fe, Ca, Ti and Sc) from A1 had the intercepts of almost zero (for instance Fig. 6(a) and (b)) and their slopes (Ti/AI: 0.054, Fe/AI: 0.58) were consistent with crustal abundance (0.054 and 0.62, respectively). But the intercepts of the regression lines of K and M n from A1 were not zero (Fig. 6(c) and (d)), they were considered to get a little contribution from other anthropogenic sources in addition to soil. Whereas as Mg (and also St) had a contribution from sea salt in addition to soil, the intercepts of their regression lines were not zero either (Fig. 7(a)). If we plot the scatter diagram between A1 and soil-derived Mg, which is calculated by Equation (1), it is found that they are highly correlated and its intercept was almost zero (Fig. 7(b)), indicating that Mg had two sources; soil and sea salt. Soil Mg = total M g - 0 . 1 2 0 × sea salt Na
(1)
0.120 was ratio of Mg to Na in sea water (Weast, 1978) sea salt Na = total N a - s o i l Na soil Na = 0.348 x AI (from crustal abundance). As mentioned above, SO 2- had correlations with V, Ni, NH,~ and C, as shown in Fig. 5. From the scatter diagram of excess-SO 2- vs N H 2 (Fig. 8), it can be found that only a half of SO 2- is neutralized by N H ~ , which means at least half the residue exists as H2SO 4 or most sulfate exists as NH4HSO 4, even though gaseous N H 3 may neutralize these acids on the filter
both during and after sampling. A photograph of the aerosol, collected on the electron microscope grid covered with thin film of formval by using an electrostatic aerosol sampler, is shown in Fig. 9. Many particles have the morphology characteristic of H2SO 4 or NH~HSO4 as reported by Ferek e t a / . (1983). Therefore, it was considered that most of the H2SO 4, which is produced by the conversion from SO 2, was not neutralized by NH3, because the concentration of NH 3 was low over the ocean (Okita et al., 1986). The negative value of the correlation coefficient for C I - - S O ~ - (Fig. 5) suggested that acidic SO~ particles caused C1- loss. This CI loss by H2SO 4 particles probably occurred on the filter during the sampling period. Aerosols having a satellite ring like Fig. 9 were observed in both summer and winter, which was consistent with the result that the ratio of NH~ to S O l - was low in both summer and winter, as shown in Fig. 8. Zn, Cu, Pb, As and Cd had some correlations with each other and especially Z n - C u , Z n - P b and P b - A s were significant. Zn and Pb also indicated some correlations with soil components. But the correlation coefficients, calculated based on concentrations in aerosol instead of the atmosphere, did not show good correlations, so that their relations were considered to be insignificant.
HITOSHIMUKAZet al.
1386
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Fig. 7. Scatter diagrams of (a) Mg and (b) soil Mg vs AI. Soil Mg is calculated by Equation (1) in the text. Triangle plots indicate the summer samples (May-October) and circle plots indicate winter samples (November-April).The equation of regression line and correlation coeflicient(R) are shown in each figure. 2 , NH4 -
[
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x Ex-S04
+ (-1.BBE-I) / ,¢
%
/1
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Fig. 8. Scatter diagram ofNH,~ vs excess-SO2-. Dashed line represents an equivalent position of sulfate and ammonium. Triangle plots means summer samples (May-October) and circle plots means winter samples (November-April). 3.5. Seasonal differences ofPb/Zn and excess-SO]- / V ratios In most cases, there were little differences between summer and winter samples in scatter diagrams of
elements, as shown in the last section. But the seasonal characteristics were found in the relations of Pb vs Zn and excess-SO 2- vs V. Figures 10 and 11 show the scatter plots of these pairs. In both cases, winter samples (circle plots) had higher values in slopes of their regression lines. This means that Pb and SO~are concentrated to Zn and V, respectively in winter. Figure 12 shows the averaged ratios of Pb to Zn in aerosol in winter (December 1983-March 1984) at several sites of Japan in addition to the Oki Islands, which were calculated from NASN data (Air Quality Bureau, Environment Agency, Japan, 1984). These sampling sites include not only several urban areas but also rural areas such as mountainous sites. The values of many sites were under 0.67, despite that the northern city, where coal is used as a fuel for heating the home in winter, had a lower value (for instance 0.198). But that of the Oki Islands (1.13) is at least two times higher than those, indicating that the somewhat different aerosol from Japan was observed on this island in winter; the average of this ratio on the Oki Islands for 4½ years was 0.97+0.15 in winter but 0.66+0.13 in summer. Oblad and Selin (1986) pointed out that the ratio of Pb to Br in aerosol at a background site in Sweden changed with the air mass trajectories. In view of the main wind direction in winter at the Oki Islands, this high value of the ratio of Pb to Zn may be due to the transport of Pb-concentrated aerosol from the Asian Continent. On the Oki Islands, wind direction apparently changes with season because of the monsoon. As the major wind direction is not so influenced by local winds on a small island, the surface wind direction observed on this island is not different basically from the wind direction at high altitudes such as the 850 mb level. In Fig. 13, surface wind directions are classified into the wind from the main land of Japan (NE-E-S-WSW) and from the direction of the Asian Continent (W-NW-N), and their frequencies are plotted for each month. Based on these data, 60-75% of wind directions in winter are found to be from the direction of the Asian Continent, whereas in summer the wind from the mainland of Japan is dominant. Since leaded gasoline is still in use in Asian coun, tries, a high concentration of Pb in the air has often been reported. Rho (1984) reviewed the pollution in Korea and introduced Pb concentrations to be 1240-3180 ngm -3 in 1977-1978. The ratio of Pb to Zn was also calculated to be 3.9-5.5 from this data. This high ratio is probably due to the enrichment of Pb by the large contribution from leaded gasoline. However, as the production of unleaded gasoline have been started since mid-1987 in Korea (Kim and Cho, 1986), atmospheric Pb concentration is expected to decrease gradually in the future. In China, leaded gasoline was also used, but Dod et al. (1986) reported that most atmospheric Ph (143 531 ngm 3) in China was derived from coal combustion. The ratio of Pb to Zn was 0.424).82, which were slightly high values compared to those of typical cities in Japan (0.204).67)
Chemical composition variation of aerosol
1387
I O
O
O
1
pm
Fig. 9. Transmission electron microscopic image of aerosol particles collected on the grid by using electrostatic aerosol sampler on 27 February in 1987 on the Oki Islands. The grid was prepared with a formval film, coated with carbon. Many particles have ring-like satellites. These particles may be H2SO 4 mists and (NH,;)HSO4.
30 Pb -
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Fig. 10. Scatter diagram of Pb concentration vs Zn concentration in the atmosphere on the Oki Islands. Winter samples (November-April), indicated by circle plots, are showing the different relation from that of summer samples (May-October), which are indicated by triangle plots. Correlation coefficients for winter and summer samples were 0.829 and 0.873, respectively. Average lead concentrations in winter and summer were 15.0 and 9.5 ngm -3, respectively.
Fig. 11. Scatter diagram of excess-SO42 vs V-sV(total V - s o i l V), which means non-soil-V. Group of winter (November-April) samples (circles) and summer (May-October) samples (triangles) had somewhat different slopes each other. Correlation coefficients for two groups were 0.534 and 0.623, respectively. Average concentrations of excess-SO]- in summer and winter were 3.66 and 3.36/~gm -3, respectively; those of V-sV were 1.57 and 0.96 ngm -3.
(Fig. 12). C o n t r a r y to those, atmospheric Pb concent r a t i o n in J a p a n was reported to be 28-170 n g m - 3 in 1984 (Air Quality Bureau, E n v i r o n m e n t Agency, Japan, 1985). Leaded gasoline is rarely used in J a p a n a n d its p r o d u c t i o n h a s been stopped since 1987. This ratio
on the Oki Islands in s u m m e r decreased to a r o u n d 0.5, which is consistent with the Japanese value. Thus, the ratio of P b to Z n m a y be a good indicator of t r a n s p o r t of aerosol from the Asian Continent,
AE(A) 24:6-0
1388
HITOSHIMUKAI et al.
0.19~ ~/ MeanPb/7.nRatio / JO 662~ ~, (1983'De¢~1984'Ma~0.3281 0"4054'
~., ~'~
1:13~O.524
1
,~0.349
- s,
,
~Q~ 0.495 ~(Dec.1984-Mar.1985) Fig. 12. Pb/Zn ratios in aerosols in winter at several sites in Japan. These values are calculated from the date of National Air Surveillance Network (Air Quality Bureau, Environment Agency,Japan, 1984, 1985).
100
,
,
,
,
,
,
+
,
,
,
o 50 g
u.P i
i
i
1
i
i
Month Fig. 13. Frequencies of the wind directions observed on the Oki Islands for 10 years. The wind directions are classified into the wind (-O-) from the main land of Japan (from NE via E and S to WSW) and (-O-) from the direction of the Asian Continent (from W via NW to N). These data are calculated from the table by The Japan Meteorological Agency (1977).
despite further detailed studies being needed. Of course, since the Pb concentration in the atmosphere was higher in winter than that in summer, its concentration itself is also considered to be an indicator. But absolute concentrations of elements in the atmosphere vary with meteorological condition, so that the ratios between elements are better indicators than such concentrations. The similar situation as above were seen in the relation between V and SO 2-. As in Japan most SO 2 is derived from oil burning, SO 2- and V have some positive correlation. By the data of Mamuro and
Mizohata (1978), the ratio of SO¢2- to non-soil-V in aerosol was 830 on average with the range (530-1150) in Japan. Whereas in the countries where coal is used as a main fuel, the ratio of SO 2- to V may be smaller than that in Japan, because V is not so enriched in coal. However, the relative SOJ- concentration increases with time by the conversion of gaseous SO 2 and the ratio of SO 2- to V also increases with time. Therefore, it is not possible to compare the ratio in Japan to those in other countries directly. For instance, Dod et al. (1986) showed S/V ratio in Beijing (China) and the ratios of SO 2- to non-soil-V were calculated to be 220-590, which are somewhat small values in comparison with the value in Japan contrary to the above assumption. But, when the molar ratio of particulate S (SO 2 ) to gaseous S (SO2) in Beijing (about 0.1) is taken into consideration, these ratios (220-590) in Beijing are considered to increase beyond the ratio in Japan (830) if enough time goes by, because the ratio of particulate S to gaseous S in Japan is about 0.3 (Matsuda and Mamuro, 1978). In the interior of Japan, the ratio in aerosols, which are retained for a long time in the air, seems to be high. By the data measured on the Ogasawara Islands (Yoshizumi and Asakuno, 1986), which are 1000 km from the mainland of Japan, the ratio of excess-SO 2- to V was about 2500 in winter. As shown in Fig. 11, the ratio of excess-SO 2- to non-soil-V (total V - s o i l V; soil V=0.00148xA1 (Mizohata and Mamuro, 1980)changed seasonally on the Oki Islands. The ratio was 3740+ 1120 in winter and 2420 + 720 in summer on average. Although it was difficult to compare the absolute values of ratios to those at other sites such as Japanese cities, Beijing, from the above reasons, the good correlation with the variation of Pb/Zn ratio, which is illustrated in Fig. 14, suggested that this seasonal difference also indicated the difference of the origin of aerosol between summer and winter; probably indicating the difference of source of SO 2- in the atmosphere or the transported distance of SO ] - . In addition, Pb/V and Pb/SO 2- ratios may also be good indicators showing the seasonal difference of aerosol composition, because the proportions of the emissions of such fuel-related components are different for each country. However, as for the values of Pb/Zn and S O l - / V , since sampling periods used in this study were too long to clarify the relations between the variations of these ratios and meteorological conditions, further studies based on a shorter sampling period will be needed for confirming the above explanations.
4.
CONCLUSIONS
Over 4 years of measurements of aerosol composition on the Oki Islands in the Sea of Japan gave much significant information on regional background levels of aerosol and the transport of aerosol around the Sea
Chemical composition variation of aerosol
1389
1O000
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llllli[ILll
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1985
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1988
Fig. 14. Variations of Pb/Zn ratio and excess-SO] / ( V - soil V). They are showing the similar variation pattern; they are high in winter (December-February) and low in summer. of Japan. The trends of changes of elemental concentrations for this sampling period were also studied, but there are no c o m p o n e n t s which indicated remarkable changes in a n n u a l m e a n concentrations. Only C showed a slight increase. Kosa, soil dust from the Asian deserts, influe~lced the c o n c e n t r a t i o n s of soil c o m p o n e n t s ih aerosol in spring and increased the concentration levels of soil elements by up to 5 times as much as those of nonKosa seasons. Therefore, a n n u a l average concentrations of soil-related elements were also relatively high c o m p a r e d to other countries such as Sweden. Sulfate c o n c e n t r a t i o n s were rather high c o m p a r e d to other b a c k g r o u n d sites. Especially, high concentrations of b o t h SO42- and V in s u m m e r suggested that SO42 - was t r a n s p o r t e d from m a i n l a n d Japan. In winter, V c o n c e n t r a t i o n s was lower, however, the S O l c o n c e n t r a t i o n did not decrease so much, so the ratio of S O ] - to V showed different values between s u m m e r and winter. F r o m the electron microscopic observation of aerosol, most particles containing S O l - were found to exist as H 2 S O 4 mists. Correlations a m o n g elements were studied and such information on their origins (soil, sea salt, oil b u r n i n g a n d so on) of these elements was obtained. Particularly, P b and Z n showed good correlation in each season. The P b / Z n ratio increased in winter a n d its value was different from those of typical Japanese cities. In view of the use of leaded gasoline in Asian countries, the high P b / Z n ratio and the high concentration of P b in winter were presumed to be due to the t r a n s p o r t of aerosol, in which Pb was concentrated, from the Asian Continent. In addition, SO~ / V ratio was found to suggest the seasonal differences of origins of aerosols.
Acknowledgements We are very grateful to members of Saigo Health Center and NTT (Saigo) for their assistance in field work. The helpful suggestions of Dr Y. Yokouchi, Dr T. Fujii, Dr M. Nishikawa and Dr A. Tanaka are gratefully acknowledged.
REFERENCES
Air Quality Bureau, Environment Agency, Japan (1984) Ippan kankyou taiki sokuteikyoku sokutei kekka houkoku, 1983 (annual report on the results of measurements of air pollutants in Japan in 19837, pp. 2274-2280. Air Quality Bureau, Environment Agency, Japan (1985) lppan kankyou taiki sokuteikyoku sokutei kekka houkoku, 1984 (annual report on the results of measurements of air pollutants in Japan in 1984), pp. 2298 2315. Arao K., Makino Y. and Nagaki Y. (19791 Some statistical aspects of yellow sand. Sci. Bull. Fac. Educ., Nagasaki Univ. 30, 65 74. Brosset C. (1976) Airborne particles: black and white episodes. Ambio 5, 157 163. Darzi M. and Winchester J. W. (1982) Aerosol characteristics at Mauna Loa observatory, Hawaii, After east Asian dust storm episodes. J. 9eophys. Res. 87, 1251 1258. Dod R. L., Giauque R. D. and Novakov T. (1986) Sulfate and carbonaceous aerosols in Beijing, China. Atmospheric Environment 20, 2271 2275. Duce R. A., Unni C. K. and Ray B. J. (1980) Long-range atmospheric transport of soil dust from Asia to the tropical North Pacific: temporal variability. Science 209, 1522 1524. Duce R. A., Arimoto R., Ray B. J., Unni C. K. and Harder P. J. (1983) Atmospheric trace elements at Enewetak Atoll: 1, concentrations, sources, and temporal variability. J..qeophys. Res. 88, 5321 5342. Ferek R., Lazrus A. L. and Winchester J. W. (1983) Electron microscopy of acidic aerosols collected over the northeastern United States. Atmospheric Environment 17, 1545-1561. Harrison R. M. and Pio C. A. (1983) Size-differentiated composition of inorganic atmospheric aerosols of both marine and polluted continental origin. Atmospheric Environment 17, 1733 1738. Hauhs M. and Wright R. F. (1986) Regional pattern of acid deposition and forest decline along a cross-section through Europe. Water, Air Soil Pollut. 31,463~474. Hitchcock D. R., Spiller L. L. and Wilson W. E. (1980) Sulfuric acid aerosols and HCI release in coastal atmosphere. Evidence of rapid formation of sulfuric acid particulates. Atmospheric Environment 14, 165 182. Ito T., Okita T., Ikegami M. and Kanazawa I. (1986) The characterization and distribution of aerosol and gaseous species in the winter monsoon over the western Pacific Ocean. II The residence time of aerosols and SO z in the long-range transport over the ocean. ,I. atmos. Chem. 4, 401M.I 1.
1390
HITOSHI MUKAI et al.
Ishizaka Y. (1972) On materials of solid particles contained in snow and rain water: part 1. J. Met. Soc. Japan. 50, 362-375. Ishizaka Y, Ono A. and Kadowaki S. (1981) Size distribution and mineral composition of yellow sand in the air over Japan and its main origins (in Japanese). Tenki 28, 651-665. Kim Y.-K. and Cho K.-R. (1986) The motor vehicle emissions control program in Korea. Proceedings of the Second Joint Conference of Air Pollution Studies in Asian Areas (Japan Society of Air Pollution), pp. 100 110. Lannefors H., Hansson H.-C. and Granat L. (1983) Background aerosol composition in southern Sweden fourteen micro and macro constituents measured in seven particle size intervals at one site during one year. Atmospheric Environment 17, 87-101. Mamuro T. and Mizohata A. (1978) Multielement analyses of airborne particulates over various areas in Japan (I) (in Japanese). J. Japan Soc, Air Pollut. 13, 357-364. Matsuda Y. and Mamuro T. (1978) Simultaneous analysis of gaseous and particulate sulfur in the atmosphere by X-ray fluorescence spectrometry (II) (in Japanese). J. Japan Soc. Air Pollut. 13, 76 83. Meteorological Research Institute, Japan (1978) Development of monitoring techniques for global background air pollution. Technical Reports of the Meteorological Research Institute 1, pp. 1-177. Mizohata A. and Mamuro T. (1980) Chemical elemental balances and identification of air pollution sources in Sakai, Osaka (I) (in Japanese). J. Japan Soc. Air Pollut. 15, 198-206. Okita T., Okuda M., Murano K., Itoh T., Kanazawa I., Hirota M., Hara H., Hashimoto Y., Tsunogai S., Ohta S. and Ikebe Y. (1986) The characterization and distribution of aerosol and gaseous species in the winter monsoon over the western Pacific Ocean: I--Measurements taken on islands and on board a ferry boat. J. atmos. Chem. 4, 343-358. Oblad M. and Selin E. (1986) Measurements of elemental composition in background aerosol on the west coast of Sweden. Atmospheric Environment 20, 1419-1432. Ottar B. (1976) Monitoring long-range transport of air pollutants: the OECD study. Ambio 5, 203-206. Ottar B. (1981) The transfer of airborne pollutants to the Arctic region. Atmospheric Environment 15, 1439-1445. Prospero J. M., Savoie D. L. and Nees R. T. (1985) Particulate sulfate and nitrate in the boundary layer over the North Pacific Ocean. J. 9eophys. Res. 90, 10,586-10,596. Rho C.-S. (1984) Chemical pollution in Korea: An experience
of the developing countries. Studies in Environmental Chemistry for Protection of the Environment (edited by Pawlouski: L., Verdier A. J. and Lacy W. J.), 23, pp. 65-76. Elsevier Science, Amsterdam. Reiter R., P6tzl K. and Sladkovic R. (1984) Determination of the concentration of chemical main and trace elements (chemical matrix) in the aerosol from 1972 to 1982 at a North-Alpine Pure Air Mountain Station at 1780 m a.s.l. Part I: methods of measurement, total concentrations, families of elements, annual variations, trend analysis. Arch. Meteor. Geophys. Bioclimatol. B 34, 215-241. Reiter R., Sladkovic R. and P6tzl K. (1987) Marked changes in the aerosol chemical matrix recently observed at 1780 m a.s.1. (BAPMoN Mountain Station) and results of first comparisons with samples obtained simultaneously at 740 m a.s.1. Met. Atmos. Phys. 36, 83-88. Rosen H., Novakov T. and Bodhaine B. A. (1981) Soot in the Arctic. Atmospheric Environment 15, 1371-1374. Rosen H. and Novakov T. (1983) Combustion-generated carbon particles in the Arctic atmosphere. Nature 306, 768-770. Saltzman E. S., Savoie D. L., Prospero J. M. and Zika R. G. (1986) Methanesulfonic acid and non-sea-salt sulfate in Pacific air: regional and seasonal variations. J. atmos. Chem.4, 227-240. Schofield C. L. (1976) Acid precipitation: effects on fish. Ambio 5, 228-230. Stelson A., Friedlander S. K. and Seinfeld J. H. (1979) A note on the equilibrium relationship between ammonia, nitric acid and particulate ammonium nitrate. Atmospheric Environment 13, 369-371. Taylor S. R. (1964) Abundance of chemical elements in the continental crust: a new table. Geochim. Cosmochim. Acta 28, 1273-1285. The Japan Meteorological Agency (1977) Frequency table for wind direction and speed (1967-1976). Technical Data Series 42, pp. 171-172. Uematsu M., Duce R. A., Prospero J. M., Chen L., Merrill J. T. and McDonald R. L. (1983) Transport of mineral aerosol from Asia over the North Pacific Ocean. J. geophys. Res. 88, 5343-5352. Weast R. C. (1978) Handbook of Chemistry and Physics, 59th edition (1978-1979). p. F-203. CRC Press, Florida. Wright R. F. and Gjessing E. G. (1976) Acid precipitation: changes in the chemical composition of lakes. Ambio 5, 219-223. Yoshizumi K. and Asakuno K. (1986) Characterization of atmospheric aerosols in Chichi of the Ogasawara (Bonin) Islands. Atmospheric Environment 20, 151-155.