Seasonal variation of methanesulfonic acid in the atmosphere over the oki islands in the sea of ] Japan

Pergamon

Atmospheric

Enuironment Vol. 29, NO. 14. pp. 1637-1648, 1995 Copyright 6 1995 Elsewer Science Ltd Printed in Great Britain. All rights reserved 1352-2310’95 S9.50 + 0.00

1352-2310(95)00057-7

SEASO.NAL VARIATION OF METHANESULFONIC ACID IN THE ATMOSPHERE OVER THE OK1 ISLANDS IN THE SEA OF JAPAN HITOSHI MUKAI and YOKO Global Environment

YOKOUCHI

Research Group, National Institute for Environmental Tsukuba, Ibaraki, 305 Japan

Studies, 16-2 Onogawa,

and MOTOYUKI

SUZUKI

Industrial Institute of Science, University of Tokyo, 7-22-l Roppongi, Minato-ku, Tokyo, 106 Japan

(First received 16 April 1994 and in final form 18 January 1995)

Abstract-Seasonal variation of methanesulfonic acid (MSA) in the atmosphere over the Oki Islands in the Sea of Japan was measured over a 9-year period. The results show that the variation was strongly influenced by the primary production activity (e.g., phytoplankton) in the sea around the islands. The MSA concentration ranged from 3 to 95 ngm-j, which is very similar to the previously reported data for islands at similar latitude, such as Norfolk Island and Cape Grim. The seasonal maximum of the MSA concentration occurred in May or June, corresponding to the spring bloom of phytoplankton in the Sea of Japan. These maximum values differed from year to year, affected by the algal growth activity and the weather conditions (e.g. amount of rainfall) during the year. Higher densities of phytoplankton and higher MSA concentrations seemed to be related to the coldness of the air and to the deeper mixing of the sea surface water that occurred during the winter just before that spring.

The non-sea-salt (NSS)-sulfate concentration was significantly higher than the expected concentration originating from the dimethylsulfate (DMS) decomposition in the atmosphere. This means that the anthropogenic sulfur compounds considerably contributed to the NSS-sulfate concentration on this island. The seasonal variation of MSA clearly differed from that of the atmospheric methylarsenic compounds (which may be produced biologically in the sea and then released into the atmosphere), suggesting differences in their sources and production mechanisms. Key word index: Methanesulfonic acid, algal bloom, the Sea of Japan, seasonal variation, trend.

1. INTRODUCI’ION

In the atmosphere, methanesulfonic acid (MSA) is an important intermediate product in the decomposition of dimethylsulfide (DMS). DMS is mainly produced biologically in the sea by phytoplankton (e.g., the Dinophycese and the Prymnesiophyceae) via three biological processes: metabolic exertion, grazing, and senescence, with the latter two processes probably being the major DMS sources (Vairavamurthy et al., 1985; Turner et al., 1988; Nguyen et al., 1988; Keller et al., 1989; Belviso et al., 1990; Burgermeister et al., 1990; Gibson et al., 1990). This biogenic DMS is then released into the atmosphere (Andreae and Raemdonck, 1983; 13ates et al., 1987). Moller (1984) estimated that about 30 Tg-S yr-’ of DMS comes from the whole ocean and about 10 Tg-S yr- r comes from all the continents. Recently, Erickson et al.

(1990) estimated the global oceanic emission of DMS at 15 Tg-S yr-‘, which is less than half of that previously estimated by Andreae and Raemdonck (1983), namely, 38 Tg-S yr - I. Such amounts of DMS, however, are still considerably large compared with the emission of anthropogenic SO*, namely, about 126 Tg-S (Dignon and Hameed, 1989). Charlson et al. (1987) suggested that DMS emission controls the concentration of NSS (non-sea-salt)-sulfate aerosol, which is cloud condensation nuclei in the atmosphere, thus influencing cloud formation, which in turn influences the Earth’s climate. DMS is decomposed by OH and NO3 radicals (Plane, 1989), producing SO1 and MSA (Hatakeyama et al., 1982; Niki et al., 1983; Grosjean, 1984; Hynes et al., 1986). Daytime reaction of DMS with OH is thought to proceed via two pathways; proton abstraction by OH and the addition of OH to the S atom.

1637 AE 29:14-D

H. MUKAI et al.

1638

The addition of OH to DMS produces MSA, dimethylsulfoxide, and dimethylsulfone finally (Plane, 1989). Furthermore, this OH addition reaction is faster at lower temperatures (Hynes et al., 1986). On the other hand, SO2 is well produced via the proton abstraction pathway. As for the yield of S02, however, Yin et al. (1990) summarized the results of the chamber experiments to have a wide range (21-74%). In general, the presence of higher NO, in the chamber gave lower SO2 and higher MSA yields. Since the oxidation of DMS with NO3 radicals is estimated to produce SOZ and MSA at a ratio of 1: 3 (Jensen et al., 1991), polluted air may produce more MSA than does unpolluted air, as suggested by the field data of Mihalopoulos et al. (1992). Thus, although the yield of MSA from DMS may vary with the atmospheric conditions (e.g., temperature, and other matrix constituents), MSA is an important degradation product of DMS. MSA was found in ambient air by Panter and Penzhorn (1980). Since then, seasonal variation of MSA has been reported for several islands in the Pacific Ocean (Saltzman et al., 1986), for Tasmania (Ayers et al., 1986,1991), and for Plymouth in the U.K. (Watts et al., 1987,199O). In most cases, the maximum concentration occurred in the summertime. At low latitudes, however, there was no clear seasonal variation and the concentrations were relatively low (Savoie et al., 1994). Saltzman et al. (1986) found high MSA concentrations at Shemya located in western North Pacific, where primary productivity is high. In general, at continental shelf areas, primary production is higher than that in the open ocean and the production activity of DMS is thought to be high. The

production activity of DMS must affect MSA concentration in the atmosphere, because Ayers et al. (1991) pointed out the correlation between MSA and DMS concentration for Cape Grim. Although, the sea near the Asian continent has relatively high primary productivity, there is no systematic data on MSA in this region. In this study, we present the seasonal variation of MSA in the atmosphere over an island in the Sea of Japan measured over a 9-year period (1983-1992). We also discuss the relationship between this variation and the scale of phytoplankton bloom around this island. In addition, we compare this variation of MSA with the variation of methylarsenic compounds (also in the atmosphere), which are biologically produced, and discuss the differences in their sources.

2. EXPERIMENTAL

The samples were collected at two sites at Dogo Island on the Oki Islands, as shown in Fig. 1. Station 1 was on a mountain top (200 m above sea level) and had little contribution from the human activity occurring on this island. Station 2 was on the roof of a five-storey office building in the downtown area and faced Saigo Bay, in which some fishing boats and a ferryboat were present. The sample at station 2 was considered as the surface level sample, and was possibly influenced by both phytoplankton activity in Saigo Bay and human activities. At each station, a low-volume air sampler (Shintaku Co., Japan) collected airborne particulate matter at an air flow rate of 20 emin- ’for a sampling time of about one month (from the 20th of the month to the 20th of the next month). The sampler had a cyclone-type classifier, thus particles larger than 10pm were excluded from the sample. Each sample was collected on a quartz-fiber filter (110 mm in

I I

I I I I I

Oki Islands

I I I

r-J50

- SETONAIKAI

:I, 100

I PACIFIC 120

OCEAN

140

Fig. 1. Sampling stations on the Oki Islands. PM line and PN line are the sampling lines of sea water by the research ships conducted periodically by Japan Meteorological Agency (1984-1992).

Seasonal variation of methanesulfonic acid

1639

Table 1. The operating conditions for the ion chromatography Eluent A Eluent B Column Suppressor Detector Eluent for rate Suppressor flow rate Gradient program (?<) Eluent A 100 100 Eluent B 0 0

1 mM NaOH 200 mM NaOH (with anion trap column, ATC-10) HPICAS6 + AG6 + AG6 AMMS (25 mM H2 SOJ electric conductivity detector 1 mlmin-’ 15 ml min-’

2 8

60

I .z

40

b P

2

86 14

62 38

0 100

0 100

100 0

+

20

Room Temp.

+

60-c

-)_

100-c

IO

20

30

Day

diameter, PALLFLEX 2500 Qast, Putnum). Each filter was stored in a cold room ( - 20°C) until it was analyzed. The sampling at station 1 was carried out from December 1983 to December 1992. The sampling at station 2 was done from February 1988 to De:cember 1992. Gradient ion chromatography (Dionex 4000i) was used to analyze MSA. First, we cut a small sample from the loaded filter (one-eighth of the filter), and then extracted the MSA and other ionic species from this sample by placing it in an ultrasonic bath for 15 min with 10 ml of deionized water with occasional shaking, followed by the fully shaking for extracting. Table 1 shows the analytical conditions for the gradient elution. (Prior to use, we det:assed the eluent by evacuating it for 30 min in an ultrasonic bath using an aspirator). After injecting the resulting sample solution into the chromatograph, MSA eluted after about 9 min, which was between the elution of formate (7 mm) and chloride (13 min). The peak areas of MSA in the chrom;atogram of the samples were integrated using an integrator (Hitachi chromate-integrator D-2000), and the MSA concentration was calculated by comparing the concentration with those of standard solutions. The detection limit of MSA was around 0.02 ppm in the solution sample. The reproducibility of the analysis was about 3%, which is the relative standard deviation of the repeated measurements of a 1 ppm solution. Other ionic species (e.g., nitrate, sulfate, and sodium) were determined using ion chromatography under an ordinal condition to calculate NSS-sulfate: NSS-sulfate = sulfate - 0.25 x sodium.

3.1. Preservability of MSA on ajlter

Since there was a possibility that a part of the collected MSA had evaporated from a filter while sampling because of the warm temperature (as high as about 60°C) in the sampler and of the long sampling period (1 month), we studied the effects of temperature and the sampling time on the recovery of MSA from a filter. We added 10 pg of MSA to each of several quartz-fiber filters, and then kept the filters under three different temperatures, room temperatures, 6O”C, and lOO”C, for one month. As shown in Fig. 2, for the room temperature and an almost

100% recovery

“‘{

100

50

0

0

50 MSA concentration

100 at Station

150 2 (ng/m3)

Fig. 3. Relation of MSA concentration between stations 1 and 2 for 1988-1992.

have risen to about 60°C during the summer, the inside temperature must have been lower than that due to the air flow through the sampler. Therefore, from this result we estimated that there was no large decrease in MSA on the filter during sampling.

3. RESIJLTS AND DISCUSSION

60°C conditions,

Fig. 2. Residual percent of MSA on quartz filters at three different temperatures.

of the

MSA from the filter was possible throughout the one-month period. However, for the 100°C condition, about half of the MSA had evaporated from the filter after about one month. Although the surface temperature of a sampler, which was placed outdoors, may

3.2. The difference between stations The difference in the atmospheric MSA concentration between stations 1 and 2 was similar to the

difference in total particulate matter at each station; the ratio of particulate matter concentration at station 1 to that at station 2 is always around 0.7. Figure 3 shows a scatter plot of MSA concentration for stations 1 and 2. The correlation between the two sites is very good (i.e., R = 0.904), showing that there was no local influence from Saigo Bay, and that the slight difference that did exist only came from the differences in heights between the two sites. Therefore, we assumed that the source area of the MSA was not local, such as Saigo Bay, but the sea around the islands. Therefore, only the data at station 1 was used in our results and discussion,

1640

H. MUKAI et al.

D

‘84

‘85

‘86

‘87

‘88

J

‘91

Month

Fig. 4. Seasonal variation of MSA in the air at station 1 from December in 1983 to December in 1992.

3.3. Seasonal variation

of MSA

Figure 4 shows the seasonal variation of MSA concentration in the atmosphere at station 1 over a g-year period, and Fig. 5 shows the averaged seasonal variations at stations 1 and 2. Both stations had a similar seasonal pattern, namely, a maximum in May or June (except in 1990 at station 2 where the maximum occurred in August) and a minimum in the winter. The concentration ranged from 5 to 130 ngmF3 at the surface level (station 2) and from 3 to 94ngmm3 at 200 m above sea level (station l), which are on the same order as those reported for Cape Grim (Ayers et al., 1986,1991), for Norfolk Island (Saltzman et al., 1986), and the Plymouth (Watts et al., 1990). These other places are located at similar latitudes as the Oki Islands and are relatively close to

-c-

Station 1 (Average for 1984-1992)

----f,----

Station 2 (Average for 1988-1992)

0 JFMAMJJASOND Month

Fig. 5. The averaged seasonal variations of MSA at station 1 (1984-1994) and station 2 (1988-1992).

a continent. The primary production at such continental shelf areas is considered to be larger than that in the open ocean. To show that the variation of MSA concentration must be influenced by the primary production activity in the seas near the islands, we first look at previously published results of primary production. Figure 6a shows the variation of chlorophyll-a in the surface sea water along the PM line (Fig. 1) in the Sea of Japan observed by the research ship of the Japan Meteorological Agency (Japan Meteorological Agency, 1988-1992). The chlorophyll-a was analyzed by fluorometry. The observations were carried out for four seasons (January-February, April-May, July-August, September-October). Since the PM line had 9 sampling points, the data for each season in Fig. 6a consists of 9 data sets along the PM line. From this figure, we see that the maximum primary production did not occur in summer (July-August) but in spring (April-May). The concentration of chlorophyll-a decreased in the summer, and then increased in the autumn. Although not enough data were available to precisely determine the month of maximum primary production in this region, according to other reports (Nagata and Kitani, 1985,1987; Kimoto et al., 1987; Nagata and Nakura, 1993) the maximum usually occurs in April and May. This period corresponded to the maximum MSA concentration in the atmosphere. Watts et al. (1990) also reported that the maximum MSA concentration at Plymouth was not in summer, such as August, but in spring, in May. However, in winter (January or February) and in autumn (September), the variation of MSA does not seem to correspond to the increase of chlorophyll-a. Turner et al. (1988) pointed out that although the DMS concentration in sea water did not always correspond to the chlorophyll-a concentration, it sometimes correlated with the amount of certain algal species. In general dinoflagellates, coccolithophores

1641

Seasonal variation of methanesulfonic acid

WSSAWSSAWSSAWSSAWSSAWSSAWSSAWSSAWSSA ‘89 PO ‘84 ‘85 ‘86 ‘81 ‘88

‘91

‘92

‘91

‘92

Season (b)

~

.._._._ __.__ +.___.. ___ PN_line

WSSAWSSAWSSAWSSAWSSAWSSAWSSAWSSAWSSA ‘85 ‘86 ‘87 ‘88 ‘89 ‘90 ‘84 Season

Fig. 6. (a) Seasonal variation of chlorophyll-a in surface water along PM line in the Sea of Japan, observed by Japan Meteorological Agency (Japan Meteorological Agency, 1984-1992). The observations were

carried out in January-February (winter), April-May (spring), July-August (summer) and SeptemberOctober (autumn). (b) Cell number density of total diatoms in the surface water along PM line (Sea of Japan) and PN line (East China Sea). These data are from Japan Meteorological Agency (1984-1992).

and some other species (Keller et al., 1989) well produce the precursor of DMS, namely, dimethylsulfoniopropionate (DMSP). Figure 6b shows the variation in cell number density of diatoms in the surface water along the PM line in the Sea of Japan and the PN line Im the East China Sea (Japan Meteorological Agency, 1984-1992). The seasonal variations in this density seem to be more sensitive to the DMS productivity than those of chlorophyll-a in that the large maximum occurred in spring, but no large increase occurred in winter. This seasonal variation seems to be more consistent with the seasonal variation of MSA concentration than that of chlorophyll-a, even though there are not so many species of diatoms that produce DMSP well (Keller et al., 1989). Since dinoflagellates, which can produce DMSP very well, increased in the Sea of Japan just

after the bloom of diatoms, the cell number density of diatoms may be a good indicator of algal growth activity. Furthermore, Fig. 4 shows that a relatively higher maximum of MSA concentration occurred in the spring of ‘84, ‘86, ‘88, and ‘89. This variation was very consistent with the variation in cell number density of diatoms during the spring. The years when a high MSA peak occurred, were always associated with a high cell number density of diatoms during that spring along the PM and/or PN line, which means that primary production in spring in the adjacent seas strongly affects the MSA concentration. (We note that a higher spring peak did not occur in 1991, despite the higher cell number density only reported at the PN line that year. This suggests that the phytoplankton activity at PN line (East China Sea), which is about

H. MUKAI et al.

1642

1000 km away from the Oki Islands, does not always indicate the good relationship to the MSA concentration in the atmosphere around the Oki Islands in the Sea of Japan.) A possible reason for the discrepancy between the minimum cell number density (for chlorophyll-a as well) observed in the summer and the relatively high peak concentration of MSA in that during the summer, air masses mainly come from the coast of the Sea of Japan, which then cross over the Setonaikai inland sea area, which has high primary productivity. In addition, there may be a grazing effect by zooplankton (Leek et al., 1990), despite that the amount of zooplankton along the PM line was not the summer (Japan always high during Meteorological Agency, 1984-1992). Furthermore, this discrepancy must be related to the yield of MSA from DMS. Since considerably high concentrations of N-related compounds, such as nitric acid, are often transported from mainland Japan to this island in summer (Mukai et al., 1990), the yield of MSA must increase due to the reaction of these compounds with NO3 radicals (Jensen et al., 1991). For further discussion of the above speculations, however, it is necessary to systematically monitor phytoplankton and zooplankton in the adjacent seas. 3.4. Interannual change of MSA As mentioned in the above section, the maximum values of MSA changed from year to year, and this change correlated well with the cell number density of diatoms during that spring (except for 1991). This means that the primary production activity strongly affected the DMS production around the island. Li et al. (1993) reported that the MSA concentration at Alert from 1980 to 1991 slightly decreased (3% per year) and that the spring peak of MSA was related to the index for the quasi-biennial oscillation (Herman et

al., 1991). The MSA concentration on the Oki Islands was also relatively low during the last three observation years, similar to the decreasing trend seen at Alert. However, the spring peak variation in MSA on the Oki Islands did not coincide with that at Alert. The summer peak variation at Alert, which is considered to be influenced basically by the primary production activity around the Arctic, may have a small anticorrelation to the variation of MSA spring peak on the Oki Islands. Therefore, it appears that the MSA concentration on the Oki Islands was affected by completely different sources from those at Alert. Figure 7 shows the air temperature on the Oki Islands. Comparing these temperatures with Fig. 5 for the MSA concentration, we see that the year having a higher spring MSA peak had a prior colder winter, as in ‘84,‘86, and ‘88. In the Sea of Japan, as in the North Atlantic (Strass and Woods, 1991; Campbell and Aarup, 1992; Sullivan et al., 1993), the algal growth is controlled by the amount of nutrients, because in the summer, phytoplankton does not grow, as seen in the chlorophyll-a data (Fig. 6a). In general, since a cold winter makes the sea surface cold, and a strong monsoon stirs the sea water (Naganuma, 1987; Hirai, 1994), sea surface water can be mixed well, resulting in more nutrients being supplied to the surface water from the deep water. Figure 8 shows the average mixing depth of sea water in winter along the PM line estimated from the temperature profile data taken by the research ships of Meteorological Agency (Meteorological Agency, Japan, 19841992). Since this observation only shows the situation of sea water temperature on a certain observation day, we cannot discuss the general situation of that during the entire winter. However, good correlation between mixing depth and cell number density of diatoms can be recognized (except for 1984), confirming the relation between colder winters and larger spring blooms.

30

o--m-T I 1 . DJDJDJAJ~JAIAJ~JAJ~ ‘84 ‘85 ‘86

‘87

‘88

‘89

‘90

‘91

‘92

Month Fig. 7. Monthly mean air temperature at Saigo on the Oki Islands from, 1984 to 1992.

1643

Seasonal variation of methanesulfonic acid

Year

Fig. 8. Mixing depth of surface sea water along PM line in winter (Japan Meteorological Agency, 1984-1992).

Legrand and Feniet-Saigne (1991) pointed out that MSA records for snow cores taken from the Antarctic might be related to strong El Nino events. They considered that the stagnation of Antarctic surface water might enhance the: primary productivity. However, since El Nino events occurred in 1982-1983, 1987-1988, and 1992, in this work the high concentration of MSA we:re considered to be observed after El Nino events (ma:y be at La Nina events). During El Nino events, MSA concentrations were relatively low. We also considered whether or not the Kosa phenomenon was responsible for supplying iron to the ocean (Martin and Fitzwater, 1988). We know the scale of the Kosa phenomenon from data for Al and Fe concentrations in the atmosphere in spring at Matsue, Shimane Prefecture, Japan (Environment Agency, Japan, 1991). In every spring, we can observe the Kosa (yellow sand) coming from the Asian deserts. A large Kosa p:henomenon was seen in 1990. Relatively smaller Kosa events occurred in ‘84,‘85, ‘88,‘89, ‘91 and ‘92. However, we had few Kosa phenomena in 1986’and 1987. Such variation was very different from that of MSA spring peak. Therefore, no relationship between this phenomenon and the MSA peak concentration was confirmed. Charlson et al. (1987) presented the increase in DMS emissions as the negative feedback mechanism of global warming. However, our results suggest a different feedback mechanism. Namely, if global warming progresses, since winters become warmer, the mixing depth of surface sea water becomes shallower, resulting in not enough nutrients being supplied to the surface water from deep water, as suggested by Williamson and Holligan (1990). As a result, the algal growth activity will decrease and the emission rate of DMS from the ocean will decrease, thus contributing to global warming. Legrand et al.

(1991) estimated that oceanic emission of DMS was lower during inter-glacial period (141-118 kyr BP,

13 kyr BP -present) compared with the last glacial period (118-13 kyr BP), based on the differences in MSA concentration between these ages seen in ice core data. Welch et al. (1993) pointed out that the MSA concentration in the ice core in Antarctica was higher when the extent of ice in the Ross Sea increased, which means a colder climate produces better conditions for algal growth. However, the results obtained here only shows the possibility of such a scenario for a short time and for a limited area, because our MSA data is not consistent with that from other observations, such as for the Antarctica (Legrand and Feniet-Saigne, 1991) and the Arctic regions (Li et al., 1993; Jaffrezo et al., 1994). Further research is necessary to understand the complex systems of algal growth in each ocean (e.g. Bakun, 1990; Leek et al., 1990; Legand and Feniet-Saigne, 1991) and to understand how the entire ocean system will change by global warming over a long-time period. In addition, since the weather (especially precipitation) also directly affects MSA concentration in the atmosphere, we must take into consideration changes in weather. In fact, we had little rain in May and June in 1989 on the Oki Islands, as shown in Fig. 9, possibly related to the highest observed MSA peak during entire observation time on the Oki Islands. 3.5. Comparison with other sites Figure 10 shows the months when the maximum MSA concentration in the atmosphere occurred (only the data of the Amsterdam Island and Baltic Sea were the DMS concentration in the atmosphere and in sea water, respectively), For easy comparison, we shifted the x-axis for the sites in the southern hemisphere by 6 months to match the seasons between the two hemispheres. The period of high MSA concentration should be related to the period of algal bloom around a sampling site. As shown in Fig. 10, the maximum

1984

1985

1986 1987 1988

1989 1990

1991

1992

Year

Fig. 9. Precipitation amount in May and July at Saigo on the Oki Islands.

H. MUKAI et al.

1644

J

A

Month(Southernhemisphere) 0 N D J FMAMJ

S

Ocean current

90

Alert

I-

SO-,

Barrow-

70 -

NorthwestScottand

ShyowaStation

7Mawson

60 - BatticSea(#)s&m 3 503

P’ymoti _J

40 L

’

OkifThiswork) M-Y ,-;;k;;;m’am -

30 -

-

warmcurrent

-

cold current

I

not classified

, Cape Grim tsland(“)

New Caledonia

20 10 o-’

buthem lmmlsphers]

hotthem hemkphed J

”

F

M

(

A

’

M

I

J

I

I

JASOND

’

t

I

’

Month (Northern hemisphere)

Fig. 10. The periods when the MSA or DMS concentration in the air show maximum. Each data is from the references as follows: Shemya, Midway, Norfolk Island and New Caledonia ia (Saltzman et al., 1986); Plymouth (Watts et al., 1987, 1990); Northwest Scotland (Davison and Hewitt, 1992);Cape Grim (Ayers et al., 1986, 1991);Baltic Sea (Leek et al., 1990); Amsterdam Island (Putaud et nl., 1992); Mawson (Prosper0 et al., 1991);Shyowa Station (Kanamori et al., 1990);Barrow (Li et al., 1993b); Alert (Li et al., 1993a). (*) means the variation of DMS in the atmosphere. In the case of Baltic Sea (#), variation of DMS in the sea is illustrated.

of MSA or DMS concentration seems to be earlier, in April-June, for the mid-latitudes (20-60”) than for the higher latitudes (greater than 60’7, in July-August. Furthermore, the sites that are influenced by cold currents seem to show a later maximum (June-August) than those influenced by warm currents. Since, in general, temperature increase is more gradual in high latitudes than in low latitudes, this tendency is understandable. For the Oki Islands, the peak MSA concentration occurred in the same month as that for Norfolk island. These islands are at similar latitude and are influenced by warm currents. For Plymouth, although its latitude is relatively high, the MSA peak appeared in the similar month to the Oki islands. This may be due to the influence from the warm current from the Gulf of Mexico. A spring maximum was also observed in Alert (Li et al., 1993). However, since sunrise occurs in spring in the Arctic region, the atmospheric conditions in Alert may be very different from those at other sites. Therefore, the spring peak of MSA at Alert may be excluded as a special case, because Li et al. (1993) reported that the summer maximum was due to DMS emission from the Arctic Ocean at that time. For the Baltic Sea, since it is not open ocean, a different situation may exist for algal growth. Leek et al. (1990) reported that DMS concentration in the Baltic Sea correlated with the variation of zooplankton, in which the grazing effect to liberate DMS was important. Figure 11 shows the ranges of MSA concentration at several sites shown in Fig. 10. Although the differences in MSA concentration were not so great among the sites, the MSA concentration was higher at the mid-latitudes (25-60”, especially 5&60”) than at the lower (10-25”) and higher latitudes (over 800).

month

Furthermore, the MSA concentration at the Oki Islands was slightly higher than that at other mid-latitude sites. Since the Oki islands are surrounded by industrialized areas, such as western Japan, and air pollutants may be sometimes transported to the islands, there is a possibility that the yield of MSA from DMS is higher than that at other cleaner sites such as Norfolk island. Also, high primary production near the Asian continent (especially near the East China Sea) may be related to the concentration of MSA. 3.6. The relation between MSA and NSS-sulfate Saltzman et al. (1983, 1986) reported that the ratio of MSA to NSS-sulfate was 5-10%. This ratio, however, may vary with ambient temperature from a few percent to close to 100% (Bates et al., 1992), and is also influenced by the presence of NO,. In our observations, since anthropogenic NSS-sulfate can be transported to the Oki Islands from mainland Japan and the Asian continent (Mukai et al., 1990), this ratio was very low (under 2%), as shown in Fig. 12. Since NSS-sulfate had high concentrations in spring and summer (during our 9-year observation period) due to the influence from mainland Japan and may be the Asian continent (Mukai et al., 1990, 1994), there was a small positive correlation between NSS-sulfate and MSA. By assuming that the ratio of MSA to NSS-sulfate is a function of temperature, as reported by Bates et al.

(1992), we calculated (using their empirical equation) a ratio of about 0.2 from the mean temperature (15°C) in May and June on these islands. Therefore, an MSA concentration of 100 ngme3 in May or June corresponds to a concentration of 0.50 pg mm3 for NSS-sulfate originating from DMS. In addition, if we

1645

Seasonal variation of methanesulfonic acid

h

2.5

% 2 6

2

.g % 1.5 g

8

I

3 0.5

0

10

20

30

40

50

60

70

80

90

Latitude Fig. 11. The ranges of MSA concentration at several sites previously reported as shown in Fig. 10. The legend is the same as Fig. 10. The data at Fanning and American Samoa are from Saltzman et al. (1986). Other data were from the same references as in Fig. 10.

3.7. Comparison with seasonal variation of methylarsenic compounds Vi’

80

60

3 %

40

B v 20 $ 0

0

2

4

6

8

NSS-Sulfate concentration (pg/m3) Fig. 12. The relation between MSA concentration and NSS-sulfate concentration in the atmosphere at station 1.

take into consideration the NO, presence in the atmosphere, the yield of MSA may reach as high as 75%, because the ratio of MSA to SOZ was reported to be 3: 1 (Jensen et al., 1991). In this case, we will be able to get a lower limit of NSS-sulfate come from DMS. If we assume that only SO2 is oxidized to sulfate, only a concentration of 0.033 pg me3 for NSS-sulfate is expected. Since an average NSS-sulfate concentration on the Oki Islands in May and June was around 5 pgm-’ (Mukai et al., 1990), we estimated that 0.7-10% of the total NSS-sulfate came from biogenic DMS. Similarly, for winter, we estimated that 0.2-l% of the total NSS-sulfate (3 pgmm3) came from DMS, suggesting that, in this region, influence from anthropogenic emission is considerably greater than from biogenic DMS from the sea.

Methylarsenic compounds are also products from the biological methylation of arsenic in pond sediment (Wood, 1974), in the sea (Andreae, 1979), in soil (Takamatsu et al., 1982), and in other environmental media (Braman, 1975; Cox, 1975; Woolson, 1977). In general, methylated arsenic is introduced into the atmosphere as volatile trimethylarsine. Trimethylarsine is oxidized into trimethylarsine oxide and dimethylarsenic acid in the atmosphere and can be detected in airborne particulate matter. Mukai et al. (1986) pointed out that the maximum concentration of methylarsenic compounds (trimethyl form + dimethyl form) in airborne particulate matter occurred in August on the Oki Islands (Fig. 13), and that the variation in this maximum concentration was strongly influenced by air temperature. Tanaka et al. (1984) also reported that a high concentration (about 170pg-Asm-“) of dimethyl form of arsenic occurred in July at Yokohama, Japan. Figure 13 shows the seasonal variations of both compounds in 1984 at the Oki Islands. Since methylarsenic compounds can be produced in the sea (Andreae, 1979), in a similar manner as MSA, we expected the same seasonal variation pattern as MSA. However, as shown in this figure, the seasonal variation of methylarsenic compounds was different from that of MSA; MSA had a peak in May and then decreased gradually, whereas the methylarsenic compounds continuously increased up to August. This difference indicates that the major source of methylarsenic compounds was not algae in the sea, because Walsh et al. (1979) estimated that the emission of methylarsenic compounds from land was larger than that from the sea. Therefore, the summer

H. MUKAI et al.

1646 ____+___ -.

MSA Methylarseniccompounds

*Oti3”

J

F

M

A

M

J

J

A

S

0

N

D

Month

Fig. 13. The comparison of seasonal variations between MSA and methylarsenic compounds (trimethyl + dimethyl form) concentrations in the atmosphere on the Oki Islands in 1984 (Mukai et al., 1986).

in the concentration of methylarsenic compounds may be influenced by the emission from not only the island itself but also the air mass coming from mainland Japan. In general, arsenic concentration is higher in the Earth’s crust (2 ppm) than in the sea (about 2 ppb), which is just the opposite for sulfur, namely, 260 ppm in the crust and 960 ppm in the sea. Such differences are considered to be essential to the difference of the emission rates of both methylated compounds from each source.

peak

4. CONCLUSIONS

Seasonal variation in the MSA concentration on the Oki Islands in the Sea of Japan was measured over a 9-year period. The concentration and the seasonal variation of MSA were similar to those for Norfolk Island and Plymouth, which are influenced by warm ocean currents. The variation for the Oki Islands was strongly influenced by the primary production activity in the Sea of Japan. The maximum MSA concentration occurred in May or June, corresponding to the spring bloom in the seas near the islands. The spring MSA peak concentration was strongly controlled by the scale of algal spring bloom during that year. Algal growth was controlled by the mixing depth of sea surface water, which was influenced by the cold weather during that winter. During the last three years in our observation period, the winter was relatively warm and a low spring MSA peak occurred, a trend that wi s similar to that reported for Alert in the Arctic. From our results, since global warming appeared to cause a decrease in the primary production around the Oki Islands, we conclude that

DMS emission from the sea around Japan did not contribute to the negative-feedback mechanism in global warming. Relatively high NSS-sulfate concentration in the atmosphere on these islands was due to the contribution from anthropogenic NSS-sulfate. We estimated the biogenic NSS-sulfate (i.e., that originating from DMS) to be at most 10% of the total NSS-sulfate during spring. Our results also show that the seasonal variation of biogenic methylarsenic compounds in the atmosphere differed from that of MSA. This suggests that the major sources of methylarsenic compounds are not present in the sea but on land. Acknowledgements-We are sincerely grateful to Mr S. Mizota, Mr S. Hashimoto, and other members of Saigo Health Center for their help in sampling. We also thank Dr H. Tanaka and Dr Shiomota (Far Seas Fisheries Research Laboratory) and Dr A. Harashima, Dr M. Kunugi, Dr C. Saito, and Dr K. Murano (NIES), for useful suggestions. We arc also indebted to Miss A. Otani, Miss M. Hiraide and Miss Y. Goto for developing the analytical technique used in determining the MSA concentrations.

REFERENCES Andreae M. 0. (1979) Arsenic speciation in seawater and interstitial water: the influence of biological-chemical interactions on the chemistry of a trace element. Limnol. Oceanogr. 24,440-452.

Andreae M. 0. and Raemdonck H. (1983) Dimethyl sulfide in the surface ocean and the marine atmosphere: a global view. Science 221, 744-747. Ayers G. P., Ivey J. P. and Goodman H. S. (1986) Sulfate and methanesulfonate in the marine aerosol at Cape Grim, Tasmania. J. atmos. Chem. 4, 173-185. Ayers G. P., Ivey J. P. and Gillett R. W. (1991) Coherence between seasonal cycles of dimethyl sulphide, methanesulphonate and sulphate in marine air. Nature 349,404~406.

Seasonal variation of methanesulfonic acid Braman R. S. (1975) Arsenic in the Environment. In Arsenical Pesticides (ACS Symp. Ser. 7) (edited by Woolson E. A.), pp. 1!08-123, American Chemical Society, Washington, DC. Bakun A. (1990) Global climate change and intensification of coastal ocean upwelling. Science 247, 198-201. Bates T. S., Cline J. D., Gammon R. H. and Kelly-Hansen S. R. (1987) Regional and seasonal variations in the flux of oceanic dimethylsulfide to the atmosphere. J. geophys. Res. 92, 2930-2938. Bates T. S., Calhoun J. A. and Quinn P. K. (1992) Variations in the methanesulfonate to sulfate molar ratio in submicron meter marine aerosol particles over the south Pacific Ocean. J. geophys. Res. 9?, 9859-9865. Belviso S.. Kim S-K.. Rassoulzadeean F.. Kraika B.. Neuven B. C., ‘Mihalopoulos N. and Bust-Menard P. 6990) Production of dim~ethylsulfonium propionate (DMSP) and dimethylsulfide (DMS) by a microbial food web. Limnol. Oceanogr. 3!3, 1810-1821. Burgermeister S. and Georgii H.-W. (1991) Distribution of methanesulfonate, NSS sulfate and dimethylsulfide over the Atlantic and North Sea. Atmospheric Environment, 25A, 587-595. Burgenneister S., Zimmermann R. L., Georgii H.-W., Bingermer H. G., Kirst G. O., Janssen M. and Ernst W. (1990) On the biogenic origin of dimethylsulfide: relation between chlorophyll., ATP, organismic DMSP, phytoplankton species, and DMS distribution in Atlantic surface water and atmosphere. J. geophys. Res. 95,20,607-20,615. Campbell J. W. and Aarup T. (1992) New production in the North Atlantic derived from seasonal patterns of surface chlorophyll. Deep-Sea Res. 39, 1669-1694. Charlson R. J., Lovelock J. E., Andreae M. 0. and Warren S. G. (1987) Oceanic phytoplankton, atmospheric sulphur, cloud albedo and climate. Nature 326, 655-661. Cox D. P. (1975) Microbiological methylation of arsenic. In Arsenical Pesticides (ACS Symp. Ser. 7) (edited by Woolson E. A.), pp. 81-96. American Chemical Society, Washington, D.C. Davison B. and Hewitt C. N. (1992) Natural sulphur species from the North Atlantic and their contribution to the United Kingdom sulphur budget. J. geophys. Res. 97, 2475-2488. Dignon J. and Hameed S. (1989) Global emission of nitrogen and sulfur oxides from 1860 to 1980. JAPCA 39,180-186. Environmental Agency, Japan (1991) Annual reports on the results of measurements of air pollutants in Japan in 1990 (in Japanese), pp. 1824. Erickson III D. J., Ghan S. J. and Penner J. E. (1990) Global ocean-to-atmosphere dimethyl sulfide flux. J. geophys. Res. 95, 7543-7552. Gibson J. A. E., Garrick R. C., Burton H. R. and McTaggart A. (1990) Dimethylsulfide and the alga Phaeocystis pouchetii in antarctic coastal waters. Marine Biology 104, 339-346. Grosjean D. (1984) Photooxidation of methyl sulfide, ethylsulfide, and methanethiol. Environ. Sci. Technol. 18, 460-468. Hatakeyama S., Okuda M. and Akimoto H. (1982) Formation of sulfur dioxide and methanesulfonic acid in the nhotooxidation of dimethvl sulfide in the air. Geoohvs. . , Res: Lett. 9. 583-586.

-

Herman J. R., McPeters R. and Stolarski R. (1993) Global average ozone chan8,e from November 1978 to May 1990. J. geophys. Res. 96, 17,297-17,305. Hirai M. (1994) Evaluation of the effects of winter cooling on sea surface temperature in the spring around Tsushima current regions. Bull. Japan Sea Nat/. Fish. Res. Inst. 44, 1-17.

Hynes A. J., Wine P. II. and Semmes D. H. (1986) Kinetics and mechanism of QH reactions with organic sulfides. J. Phys. Chem. 90, 4148-4156. Jaffrezo J.-L., Davidson C. I., Legrand M. and Dibb J. E.

1647

(1994) Sulfate and MSA in the air and snow on the Greenland ice sheet. J. geophys. Res. 99, 1241-1253. Japan Meteorological Agency (1990-1992) The Results of Ocean0 Graphical Observation 80-92, Tokyo, Japan Meteorological Agency. Jensen N. R., Hjorth J., Lohse C., Skov H. and Restelh G. (1991) Products and mechanism of the reaction between in air. Atmospheric NO, and dimethylsulphide Environment 25A. 1897-1904.

Kanamori S., Kanamori Y., Nishikawa M., Aoki S. and Watanabe 0. (1990) Trace constituents in aerosol in Antarctica. (in Japanese) Proc. Ann. Meeting of Geochemicat Sot. Jpn. in 1990, p. 17. Keller M. D., Bellows W. K. and Guillard R. L. (1989) Dimethyl sulfide production in marine phytoplankton. In Biogenic Sulfur in the Environment (edited by Saltzman E. S. and Cooper W. J.), pp. 167-182. ACS Symposium Series 393, American Chemical Society, Washington, DC. Kimoto K., Nakashima J. and Morioka Y. (1987) Standing stock of chlorophyll-a and primary productivity in a small inlet of Kyushu. (in Japanese) Bull. Seikai Region Fish. Res. Lab. 64,35-46.

Leek C., Larsson U., B&gander L. E., Johansson S. and Hajdu S. (1990) Dimethyl sulfide in the Baltic Sea: annual variability in relation to biological activity. J. geophys. Res. 95,3353-3363. Legrand M., Feniet-Saigne C., Saltzman E. S., Germain C., Barkov N. I. and Petrov V. N. (1991) Ice-core record of oceanic emissions of dimethylsulfide during the last climate cycle. Nature 350, 144-145. Legrand M. and Feniet-Saigne C. (1991) Methanesulfonic acid in south polar snow layers: a record of strong El Nino?. Geophys. Res. Lett. 18, 187-190. Li S.-M., Barrie L. A. and Sirois A. (1993a) Biogenic sulfur aerosol in the Arctic troposphere: 2 Trends and seasonal variations. J. geophys. Res. 98, 24623-24631. Li S.-M., Barrie L. A., Talbot R. W., Harriss R. C., Davidson C. I. and Jaffrezo J.-L. (1993b) Seasonal and geographic variations of methanesulfonic acid in the Arctic troposphere. Atmospheric Environment 27A, 301 l-3024. Martin J. H. and Fritzwater S. E. (1988) Iron deficiency limits phytoplankton growth in the north-east Pacific Subarctic. Nature 331, 341-343.

Mihalopoulos N., Nguyen B. C., Boissard C., Campin J. M., Putaud J. P., Belviso S., Barnes I. and Becker K. H. (1992) Field study of dimethylsulfide oxidation in the boundary layer: variation of dimethylsulfide, methanesulfonic acid, sulfurdioxide, non-sea-salt sulfate and aitken nuclei at a coastal site, J. atmos. Chem. 14, 459-477. Moller D. (1984) On the global natural sulphur emission. Atmospheric Environment 18, 29-39. Mukai H., Ambe Y., Muku T., Takeshita K. and Fukuma T. (1986) Seasonal variation of methylarsenic compounds in airborne particulate matter. Nature 324, 239-241. Mukai H., kmbe Y., Shibata K., Muku T., Takeshita K., Fukuma T.. Takahashi J. and Mizota S. (1990) Lone-term variation of chemical composition of atmospheric a&sol on the Oki Islands in the Sea of Japan. Atmospheric Enviornment 24A, 1379- 1390. Mukai H., Tanaka A., Fujii T. and Nakao M. (1994) Lead isotope ratios of airborne particulate matter as tracers of long-range transport of air pollutants around Japan. J. geophys. Res. 99, 3717-3726. Naganuma K. (1987) Some areas of fluctuations of the seasonal water temperature in the Tsushima warm current region in the Japan Sea. Bull. Jau. Sea Rea. Fish. Res. Lab. 37, l-11. Nagata H. and Kitani K. (1985) Chlorophyll-a distribution and oceanographic structure in the sea area of the San-in district in spring, 1984. (in Japanese) Bull. Jap. Sea Reg. Fish. Res. Lab. 35, 161-164. Nagata H. and Kitani K. (1987) Investigation of environmental factors concerning primary productivity in winter

1648

H. MUKAI et al.

to spring by ferry boats. (in Japanese) Bull. Jap. Sea Reg. Fish. Res. Lab. 37, 21-26.

Nagata H. and Nakura N. (1993) Seasonal changes of river discharge and chlorophyll-a concentration in Toyama Bay, southern Japan Sea. (in Japanese) Bull. Jap. Sea Reg. Fish. Rex Lab. 43, 55-68.

Nguyen B. C., Belviso S., Mihalopoulos N., Gostan J. and Nival P. (1988) Dimethyl sulfide production during natural phytoplankton blooms, Mar. them. 24, 133-141: Niki H., Maker P. D., Savege C. M. and Breitenbach L. P. (1983) An FTIR study of mechanism for the reaction HO + CHsSCH,. Int. J. Chem. Kinet. 15, 647-654. Panter R. and Penzhorn R. -D. (1980) Alkvl sulfonic acids in the atmosphere. Atmospheric‘En&onm&t 14, 149-151. Plane J. M. C. (1989) Gas-phase atmospheric oxidation of biogenic sulfur compounds: a review. In Biogenic Sulfur in the Environment (edited by Saltzman E. S. and Cooper W. J.), pp. 167-182. ACS Symposium Series 393, American Chemical Society, Wahington, DC. Prosper0 J. M., Savoie D. L., Saltzman E. S. and Larsen R. (1991) Impact of oceanic sources of biogenic sulphur on sulphate aerosol, concentrations at Mawson, Antarctica. Nature 350, 221-223. Putaud J. P., Mihalopoulos N., Nguyen B. C., Campin J. M. and Belviso S. (1992) Seasonal variations of atmospheric sulfurdioxide and dimethylsulfide concentrations at Amsterdam Island in the Southern Indian Ocean. J. atmos. Chem. 15, 117-131. Saltzman E.S., Savoie D. L., Zika R. G. and Prosper0 J. M. (1983) Methane sulfonic acid in the Marine Atmosphere. J. geophys. Res. 88, 10,897-10,902. Saltzman E. S., Savoie D. L., Prosper0 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.

Savoie D. L., Prosper0 M., Arimoto R. and Duce R. A. (1994) Non-sea-salt sulfate and methanesulfonate at American Samoa. J. geophys. Res. 99, 3587-3596. Strass V. H. and Woods J. D. (1991) New production in the summer revealed by the meridional slope of the deep chlorophyll maximum. Deep-Sea Res. 38, 35-56. Sullivan C. W., Arrigo K. R., McClain C. R., Comiso J. C.

and Firestone J. (1993) Distributions of phytoplankton blooms in the southern ocean. Science 262, 1832-1837. Takamatsu T., Aoki H. and Yoshida T. (1982) Determination of arsenate, arsenite, monomethylarsonate, and dimethylarsinate in soil polluted with arsenic. Soil Sci. 133, 239-246. Tanaka S., Kaneko M. and Hashimato Y. (1984) Chemical form and behavior of arsenic compounds in the atmosphere. (in Japanese) J. Chem. Sot. Japan 637-642. Turner S. M., Maline G. and Liss P. S. (1988) The seasonal variation of dimethyl sulfide and dimethylsulfoniopropionate concentrations in nearshore waters. Limnol. Ocenogr. 33, 364-375. Vairavamurthy A., Andreae M. 0. and Iverson R. L. (1985) Biosynthesis of dimethylsulfide and dimethylpropiothetin by Hymenomonas carterae in relation to sulfur source and salinity variations. Limnol. Oceanogr. 30, 59-70. Walsh P. R., Duce R. A. and Fasching J. L. (1979) Considerations of the enrichment, sources, and flux of arsenic in the troposphere. J. geophys. Res. 84,1719-1726. Watts S. F., Watson A. and Brimblecombe P. (1987) Measurements of the aerosol concentrations of methanesulphonic acid, dimethyl sulphoxide and dimethyl sulphone in the marine atmosphere of the British Isles. Atmospheric Environment 21, 2667-2672.

Watts S. F., Brimblecombe P. and Watson A. J. (1990) Methane sulphonic acid, dimethyl sulphoxide and dimethyl sulphone in aerosols. Atmospheric Environment 24A, 353-359.

Welch K. A., Mayewski P. A. and Whitlow S. I. (1993) Methanesulfonic acid in coastal antarctic snow related to sea-ice extent. Geophys. Res. Lett. 20, 443-446. Williamson P. and Holligan P. M. (1990) Ocean productivity and climate change. Trens Ecol. Euo[. 5, 299-303. Wood J. M. (1974) Biological cycles for toxic elements in the environment. Science 183, 1049-1052. Woolson E. A. (1977) Fate of Arsenicals in different envircnmental substrates. Environ. Health Pers. 19,73-81. Yin F., Grosjean D. and Seinfeld J. H. (1990) Photooxidation of dimethvl sulfide and dimethvl disulfide. I: Mechanism development. J. atmos. them. li, 309-364.