Impacts of the eruption of Miyakejima Volcano on air quality over far east Asia

Transcription

1 JOURNAL OF GEOPHYSICAL RESEARCH, VOL. 109,, doi: /2004jd004762, 2004 Impacts of the eruption of Miyakejima Volcano on air quality over far east Asia Mizuo Kajino and Hiromasa Ueda Disaster Prevention Research Institute, Kyoto University, Kyoto, Japan Hikaru Satsumabayashi Nagano Research Institute for Health and Pollution, Nagano, Japan Junling An Institute of Atmospheric Physics, Chinese Academy of Sciences, Beijing, China Received 11 March 2004; revised 22 June 2004; accepted 22 July 2004; published 6 November [1] A regional-scale Eulerian Model System for Soluble Particles (MSSP) was constructed to simulate environmental changes caused by a SO 2 4 increase as the result of the eruption of Miyakejima Volcano in the northwest Pacific Ocean. The measured volcanic SO 2 emission was 9 Tg yr 1 for a year from the beginning of the eruption, July It is equivalent to 70% of global volcanic emission and 6.9% of global anthropogenic emission. Seasonal variations of the volcanic sulfate increase, and change of gas-aerosol partitioning of NH 3 and ph decrease of precipitation were studied using the MSSP model for 1 year from September 2000 to August 2001, together with observations performed at Happo Ridge observatory in the mountainous area in central Japan. In winter, northwesterly wind prevails, and volcanic SO 2 4 was mainly transported southeastward to the Pacific Ocean while volcanic SO 2 4 was transported southwestward to Japan, Korea, and Taiwan, owing to the subtropical high-pressure system over the Pacific Ocean in summer. Temporal variations of SO 2 4 concentrations and gas-aerosol equilibrium of NH 3 at Happo Ridge were well-simulated. In the plume from the Asian continent, 98.7% of total SO 2 4 was anthropogenic, and 63.5% of NH 3 existed in aerosol phase as (NH 4 ) 2 SO 4. In the volcanic plume, 95.5% was volcanic, excessive sulfate fixed 100% of NH 3 into aerosol phase, and aerosol was strongly acidified. Modeled annual mean ph of precipitation in Japan decreased by , which is equivalent to neutralization by yellow sand. INDEX TERMS: 0305 Atmospheric Composition and Structure: Aerosols and particles (0345, 4801); 0345 Atmospheric Composition and Structure: Pollution urban and regional (0305); 0370 Atmospheric Composition and Structure: Volcanic effects (8409); 0368 Atmospheric Composition and Structure: Troposphere constituent transport and chemistry; 0365 Atmospheric Composition and Structure: Troposphere composition and chemistry; KEYWORDS: regional air pollution model, volcanic sulfate, anthropogenic sulfate Citation: Kajino, M., H. Ueda, H. Satsumabayashi, and J. An (2004), Impacts of the eruption of Miyakejima Volcano on air quality over far east Asia, J. Geophys. Res., 109,, doi: /2004jd Introduction [2] Since July 2000, Mt. Oyama on Miyakejima Island (written as Miyakejima Volcano hereafter), located in the northwest Pacific Ocean and 180 km south from Tokyo Metropolitan area, has begun to erupt and been emitting huge amount of sulfur dioxide. Sulfur dioxide concentration in Miyakejima Island is exceeding environmental air quality standards still now in February 2004 and residents have been evacuating from the island for 3 and a half years. Seismological and Volcanological Department of Japan Meteorological Agency (SVD-JMA) have been performing Copyright 2004 by the American Geophysical Union /04/2004JD continuous measurements of smoke height and sulfur dioxide emission of Miyakejima Volcano since September 2000, 2 months after the beginning of the eruption [Kazahaya, 2001]. According to the measurement, volcanic sulfur dioxide emission is at least 9 Tg during one year from the beginning of the observation. It is about 70% of global emission from volcanos from 1970s to 1997, that is 13 Tg yr 1 [Andres and Kasgnoc, 1998] and 6.9% of global emission from anthropogenic sources, 130 Tg yr 1, i.e., fossil fuel combustion and biomass burning in 1985 [Benkovitz et al., 1996]. The volcanic emission amounts to about a half of anthropogenic sulfur dioxide emission from China (20.4 Tg yr 1 ) and more than 10 times as that from Japan (0.80 Tg yr 1 ) [Streets et al., 2003]. The maximum value of smoke height among each observation 1of11

2 was 14,000 m near the tropopause and the maximum sulfur dioxide emission was 90,000 ton d 1, which is equivalent to whole Asian anthropogenic emission (94,000 ton d 1 ). High sulfur dioxide concentration episodes exceeding 100 ppb were reported at several monitoring stations and people complained of bad smell in many places in Japan. [3] Substantial observation of persistent sulfur dioxide emission from worldwide volcanoes has been carried out [e.g., Stoiber et al., 1983; Allard, 1997; McGonigle et al., 2003]. These emission data sets were compiled and inventoried for global and regional model use [e.g., Stoiber et al., 1987; Andres and Kasgnoc, 1998]. In terms of Miyakejima Volcano, several studies on environmental impacts of the volcanic sulfate based on observations [Katsuno et al., 2002; Fujita et al., 2003; Satsumabayashi et al., 2004, hereinafter referred to as S-04] have been carried out. However, no numerical simulation on regional-scale atmospheric impacts caused by such prominently huge eruptive sulfur dioxide emission was done for a long period although its regional impacts were supposed to be considerably large. [4] Thus in this study a regional-scale Eulerian Model System for Soluble Particles (MSSP) was constructed to simulate environmental changes caused by sulfate increase as the result of the eruption of Miyakejima Volcano, together with a ground-based observation performed by S-04, and the impacts were quantified by comparing the volcanic and anthropogenic sulfate. This study has the following features. We used continuous observation data sets of sulfur emission from the volcano and sulfur oxides concentration at a monitoring station in Japan over a long period. Together with numerical simulation, it became possible to investigate temporal and seasonal variations of environmental changes caused by the volcanic sulfur oxides in detail. The phenomenon itself was characteristic, i.e., emission, dispersion and formation of sulfur oxides from an isolated and fixed huge point source where emission flux is measured directly, compared to the case of anthropogenic sulfur emission. These conditions might be very helpful to understand mechanism of environmental effects concerning sulfate aerosol, such as short-wave scattering and activation process as cloud condensation nuclei. [5] In section 2, the construction of the MSSP model and ground-based observation method performed by S-04 are introduced. Model validations are shown in section 3. Simulation results and discussion are provided in section 4 and major conclusions are summarized in the final section. 2. Methods 2.1. Numerical Method Outline [6] The MSSP model, regional-scale Eulerian Model System for Soluble Particles, is an air quality model with a meteorological model over the east Asian region. The model has been developed to focus on behaviors of water soluble particles that affect effectively acid rain, climate change as well as cloud microphysics. The MSSP model system consists of mainly 3 parts, a meteorological model, a chemical transport model and a gas-aerosol equilibrium model. Penn State/NCAR (National Center for Atmospheric Research) Mesoscale Model, MM5 [Dudhia, 1993] is used for simulating meteorological field. Chemical transport module has been developed based on Regional Air Quality Model (RAQM) [An et al., 2002]. Simulating Compositions of Atmospheric Particles at Equilibrium (SCAPE) module [Kim et al., 1993a, 1993b; Kim and Seinfeld, 1995; Meng et al., 1995] was used for simulating thermodynamic equilibrium of aerosols. [7] The model domain includes whole east Asia from N and E with horizontally 1 by 1 degree grid interval on spherical coordinate. MSSP has vertically 23 grids on terrain-following coordinate from ground to tropopause. The model uses NCEP (National Center for Environmental Prediction) Final Analysis data (1 by 1) for initial and boundary conditions for calculating meteorological field by MM5. MM5 simulates meteorological fields, mixing ratio of hydrometeor species such as cloud, rain, ice and snow using cloud microphysics parameterization of Reisner et al. [1998], cumulus convection parameterized by Grell [1993] and turbulent kinetic energy using the theory of Mellor and Yamada [1975]. As for emissions of primary trace species, such as SO 2, NO x, NH 3, CO, NMVOCs and BC, emission inventories developed by Streets et al. [2003] are used for the model. In terms of mechanically produced natural primary aerosol emissions, dust particles deflation is calculated according to Wang et al. [2000] and emission of sea-salt particles is derived from the observation at Goto Islands in East China Sea (see the location in Figure 1). Shimohara et al. [2001] observed size distribution of aerosol and its chemical characterization at a monitoring station about 95m MSL on Goto Islands using low-volume Andersen samplers. The island is isolated and there are no large anthropogenic emission sources within or around it. There was certain correlation between wind speed and Na + concentration, which was supposed to be mostly marine origin at the station (correlation coefficient R = 0.76). We estimated average deposition flux of Na + from its average size distribution and then derived the relationship between sea-salt emission flux and wind speed under the assumption that emission flux was equivalent to deposition flux because of the certain correlation of the concentration and the wind speed. The wind speed of the lowest grids (about 50 m MSL) are used for calculating the emission in MSSP. MPMAA (A simple but accurate mass convertive peak-preserving mixing ratio bounded advection algorithm) [Walcek and Aleksic, 1998] is used for wind advection of species. Turbulent diffusivities are derived using 1.5-order closure scheme based on turbulent kinetic energy, output of MM5 [Xue et al., 1995]. To calculate gas phase chemistry, condensed Carbon-Bond IV mechanism [He and Huang, 1992; An et al., 2002] is chosen. 24 transported species and 8 radicals with 52 photochemical reactions are treated in the model. Liquid phase chemical reactions are very important for formation of sulfate. 16 ionic species with 12 solution equilibria and 30 chemical reactions are considered based on the work of Chameides and Davis [1982] and Chameides [1984] for liquid phase chemistry. The model uses Wesely [1989], Walmsley and Wesely [1996] for calculating dry deposition process of gaseous species. To estimate wet deposition processes, collision efficiency of water droplets and aerosols depending on particulate size are introduced for calculating below cloud scavenging. Water uptake by hygroscopic components calculated by SCAPE 2of11

3 Figure 1. A description of far east Asia, Happo Ridge, Miyakejima Volcano, and other locations mentioned in this paper. module are used for the estimation of nucleation scavenge. Additionally, SCAPE module can calculate compositions in aerosols at equilibrium and gas-aerosol partitioning of volatile inorganic components such as ammonia-ammonium, nitric acid-nitrates and hydrogen chloride-chlorides. [8] The output of MSSP are concentrations of gaseous species (NO, NO x, HNO 3,SO 2,NH 3, HCl, O 3, CO, VOCs, etc.) and aerosols (mineral dust, sea salt, POC, BC, SO 4 2, NH 4 +, NO 3, Cl, etc.) in each grid box, wet and dry deposition amount of each species on the ground, concentrations of each inorganic soluble component (Ca 2+,K +, Na +, Mg 2+, SO 4 2, NH 4 +, NO 3, Cl, CO 3 2 ) and water content in aerosols, concentrations of inorganic ionic compositions (same as soluble components of aerosols) in precipitation and ph values of precipitation Sulfur Dioxide Emission From Miyakejima Volcano and Other Natural Sources [9] Figure 2 illustrates time variations of measured smoke height and sulfur dioxide emission from Miyakejima Volcano, denoted as open circles. Measurement of smoke height and sulfur dioxide emission has been carried out continuously since September 2000 by SVD-JMA. Sulfur dioxide emission from Miyakejima Volcano was derived using correlation spectrometer (COSPEC) [Kazahaya, 2001]. COSPEC measures the absorption of scattered skylight by SO 2 around 300nm and uses an internal mechanical 3of11

4 Figure 2. Temporal variations of smoke height and sulfur dioxide emission from Miyakejima Volcano. Open circles are measured values by the Japan Meteorological Agency, and solid lines denote smoothed observed values using cubic spline function for the numerical simulation use. correlation procedure to yield column amounts [Stoiber et al., 1983]. COSPEC measurements involve traversing below a plume and multiplying the integrated SO 2 cross section by estimated plume transport speed to yield fluxes. This method was applied to sulfur dioxide emission from Miyakejima Volcano as well as other volcanic emissions worldwide [e.g., Andres and Kasgnoc, 1998]. [10] In order to input the volcanic emission to the model, these raw measurement data were smoothed by cubic spline function, denoted as solid line in Figure 2. Additional volcanic sulfur dioxide emission in each time step is designed to be distributed vertically in the grid where Miyakejima Volcano located, just above the crater (813 m) to the top of measured smoke height with decreasing linearly with height. Since we focus especially on anthropogenic sulfate and the sulfate from Miyakejima Volcano, emission of other volcanic sulfur dioxide and oceanic dimethyl sulfide (DMS) are not considered in this study. DMS has substantial contribution to sulfur chemistry in global scale, while the contribution is negligible over east Asian region [Carmichael et al., 2002]. Kettle and Andreae [2000] estimated global DMS flux from the ocean as TgS yr 1 using three parameterizations of DMS flux and several meteorological data sets. Using the value, DMS flux from all over the domain in this study (15 60 N, E) is estimated as TgS yr 1. The value is still low compared to total anthropogenic sulfur emission from Asia, 17.1 TgS yr 1 and volcanic sulfur emission from Miyakejima Volcano, 4.5 TgS yr 1. Thus the estimated total DMS flux is % of total sulfur emission from the domain and moreover not all of DMS can be converted to SO 2, some part of them is turned into methane sulfonic acid (MSA). Here it is also noted that the volcano is a point emission source. Thus DMS is negligible especially in the volcanic plume, which we preferentially focus on Field Observation [11] Ground based observation was made at Happo Ridge National Acid Rain Monitoring Station which is sited at 1850 m ASL, N, E, in the central mountainous area in Japan. It is located 300 km north from Miyakejima Volcano and more than 200 km from large industrial and urban areas, such as Tokyo metropolitan area and Nagoya area, as illustrated in Figure 1. Aerosol and precip- 4of11

5 Figure 3. Temporal variations of (top) measured sulfate concentration at Happo Ridge and (bottom) sulfur dioxide emission of Miyakejima Volcano. Characters in the figure denote important dates: (a) beginning of the eruption on 8 July 2000, (b) beginning of JMA measurement of smoke height and sulfur dioxide emission from the volcano, 26 August 2000, and (c and d) intensive observation periods at Happo Ridge. Numerical simulation was done for 1 year from 1 September 2000 to 31 August itation, together with gaseous pollutants have been observed from May 1998, two years before the eruption to present. Short time sampling of aerosols by middle volume air sampler was made from 1200 to 1500 LST every day, while 4-hour sampling was done consecutively four times per day starting from 0000 in intensive observation periods. One-day collection was made from 0900 LST for precipitation and every 1-hour monitoring was done for SO 2, NO, NO 2,O 3 and PM10. Water-soluble inorganic species, Na +,K +,Mg 2+, Ca 2+,NH 4 +,SO 4 2,NO 3,Cl in the aerosol and precipitation were analyzed using ion chromatography. S-04 mention sampling method and chemical analysis more in detail. [12] Shown in Figure 3 are daily variations of (above) sulfate concentration observed at Happo Ridge and (below) sulfur dioxide emission from Miyakejima Volcano measured by JMA-COSPEC. Figures 3a and 3b denote important dates. In Figures 3a, 8 July 2000 is the beginning of the eruption and In Figure 3b, 26 August 2000 is the beginning of the measurement by JMA-COSPEC. [13] As for seasonal variations of meteorological conditions over far east Asia, several kinds of meteorological systems pass eastward one after another in days to weeks cycle in spring. In rainy season from June to July, a stationary front is formed over Japan and brings persistent rain for several weeks. In summer, subtropical high pressure system over the Pacific Ocean is predominant. Tropical cyclone, called typhoon, goes from south to north in autumn and northwesterly dry monsoon is prevailing in winter. In terms of air quality variations by season, in spring contaminated air mass advection from Asian continent brings high concentration episodes of ozone, nitrogen oxides together with dust particles, so-called yellow sand, deflated from northwestern part of China. Annual mean sulfate concentration at Happo Ridge before the eruption was 2.57 mg m 3 with maxima in spring (5.50 mg m 3 in May 2000, 3.36 mg m 3 in April 2000.) due to contamination from the continent and with minimum in winter (1.09 mgm 3 in December 1999) due to stagnant photochemistry in the atmosphere. However, after the eruption, annual mean sulfate concentration increased to 3.83 mg m 3 (1.5 times larger than that before the eruption) at Happo Ridge with maxima in summer (7.82 mg m 3 in August 2000, 5.72 mg m 3 in July 2001) Analytical Periods [14] Figures 3c and 3d denote important periods of this study. Simulation is performed from 1 September 2000 to 31 August 2001 for 1 year after the beginning of the observation by JMA-COSPEC. Figures 3c and 3d are 1-month intensive observation periods when consecutive aerosol sampling was carried out at Happo Ridge, from September to October 2000 and from May to June 2001, respectively. However, since the smoke was too thick for ultraviolet beam of COSPEC to penetrate adequately during the period of Figure 3c [Kazahaya, 2001], the observation of the volcanic emission as well as simulation 5of11

6 Figure 4. A comparison of monthly mean sulfur dioxide concentration calculated by the MSSP model to observation at monitoring stations in EANET. Each symbol corresponds to each EANET station, (crosses) Banryu, (diamonds) Ogasawara, (asterisks) Ijira, (triangles) Tanzawa, and (circles) Happo Ridge. of sulfur oxides could underestimate. Thus we focus on the period of Figure 3d in this paper. 3. Validation of MSSP [15] Carmichael et al. [2002] recently summarized that long-range transports of sulfur oxides are well simulated by numerical models. However, we must confirm whether MSSP model can predict the volcanic effects on sulfur oxides concentration. Comparison of monthly mean sulfur dioxide and sulfate are presented in this section Sulfur Dioxide [16] Figure 4 is scattergram of observation and simulation of monthly mean sulfur dioxide concentration at 5 stations (Banryu, N, E, 60 m MSL; Ogasawara, N, E, 230 m MSL; Ijira, N, E, 140 m MSL; Tanzawa N, E, 920 m MSL; Happo Ridge, N, E, 1850 m MSL) in EANET (Acid Deposition Monitoring Network in east Asia) for 6 months from October 2000 to March 2001 (therefore totally 30 points in the diagram). Each symbol in Figure 4 corresponds to each EANET station, (crosses) Banryu, (diamonds) Ogasawara, (asterisks) Ijira, (triangles) Tanzawa and (circles) Happo Ridge. The locations of the stations are shown in Figure 1. Simulation results are in reasonable agreement (within factor of 2, the correlation coefficient R = 0.83) with observation in spite of the coarse grid intervals Sulfate [17] Figure 5 shows monthly variation and annual mean of sulfate concentration at Happo Ridge during the simulation periods. Boxes are observation value, closed triangles are simulation value and closed squares are simulation without the volcanic eruption, i.e., anthropogenic sulfate. The simulation results show very good agreement with observation for monthly and annual mean except for in September and from winter to spring season. The simulation underestimates observation in September because of the underestimation of COSPEC measurement as mentioned in section 2.3. The correlation coefficient R = 0.89 and the data are completely within factor of 2. The volcanic sulfate concentration was comparable to anthropogenic sulfate at Happo Ridge in annual mean and the fraction to total sulfate was 46%. The volcanic sulfate concentrations were predominant in May, October and August and the fractions to total sulfate concentration were 84.0, 61.1 and 52.4% respectively. However, the volcanic influence was less in February, December and June and the fractions of volcanic sulfate concentration to total sulfate were 11.9, 13.4 and 22.7%, respectively. It might be odd that the percentage was so low in June. The reason, which is discussed later in Section 4.1 in detail, is related to the rainy season in Japan. 4. Results and Discussions 4.1. Seasonal Variations (September 2000 to August 2001) [18] Figure 6 shows monthly mean concentration of (above) the volcanic sulfate around Japan and (below) the Figure 5. A comparison of modeled and measured monthly mean sulfate concentration at Happo Ridge. Open squares denote measured values, closed triangles denote modeled values, and closed squares are values modeled without sulfur dioxide emission from Miyakejima Volcano. 6of11

7 Figure 6. Monthly mean concentrations of (top) sulfate increase in mg m 3 caused by the eruption and (bottom) contributions of volcanic sulfate to total (volcanic plus anthropogenic) sulfate (percent) in the lower troposphere (up to about 2000 m MSL) from October 2000 to August 2001 in every 2 months from left to right. fractions of the volcanic sulfate concentration to total sulfate concentration in the lower troposphere (up to about 2000 m MSL) from October 2000 to August 2001 in every 2 months from left to right. In October when the volcanic eruption was still brisk, the volcanic sulfate concentration exceeded 5 mg m 3 (30 50% of total sulfate) over Kanto Plane, where Tokyo is located, causing widespread environmental acidification around Japan. In winter season northwesterly wind was prevailing around Japan and volcanic sulfate was mainly transported southeastward to the Pacific Ocean. The volcanic sulfate concentration over Japan was quite small (almost 0 mg m 3 ) and the maximum value all over the domain was also less in winter (3 4 mg m 3 ). However, the contribution of volcanic sulfate is quite larger (more than 50% in large area) in the Pacific Ocean in winter than other months in the year. It is indicated that in winter over the Pacific Ocean the volcanic sulfate might affect cloud properties such as size distribution and lifetime through cloud microphysics as Albrecht [1989] proposed. In spring season, as anticyclone and cyclone systems come to Japan one after another from west to east, the volcanic sulfate increased over Japan ( mg m 3 ). [19] From the beginning of June to the middle of July, a stationary front is formed near Japan Archipelago. During the season, so-called rainy season, the stationary front has a wide range from the continent to the Pacific Ocean. Since westerly wind is dominant near the front in lower troposphere and the wind pattern makes convergence zone around Japan during the season, anthropogenic sulfate was transported from the continent and the volcanic sulfate concentration was distributed long and narrowly from west to east as shown in Figure 6. Therefore the contribution of the volcanic sulfate became less in June as shown in Figure 5. [20] In summer season, the subtropical high-pressure system over the Pacific Ocean is dominant. The volcanic sulfate was transported westward to southwestward by the prevailing wind system and reached to Korea and southwestern Japan. The volcanic concentration was more than 1 mg m 3 in Korea and 2 mg m 3 around Taiwan, and the fraction was 20 30% in the regions. The volcanic sulfate concentration in the atmosphere became high again in summer although sulfur dioxide emission from the volcano has decreased with time Anthropogenic Versus Volcanic Sulfate [21] Figures 7a and 7b show temporal variations of measured sulfur dioxide concentration and sulfate concentration at Happo Ridge in the intensive observation period of Figure 3d, from 1200 LST on 15 May 2001 to 1200 LST on 11 June Two peaks of sulfate concentrations are found on 26 and 30 of May. Figure 7c shows simulated concentration of anthropogenic sulfate and wind patterns at about 1500 m MSL at 0000 LST on 26 May. Westerly wind in low pressure system on Japan Sea carried anthropogenic sulfate to Happo Ridge and 98.7% of total sulfate was anthropogenic sulfate at that time. Figure 7d shows simulated concentration of the volcanic sulfate and wind patterns 7of11

8 Figure 7. Temporal variations of measured concentrations of (a) sulfur dioxide and (b) sulfate at Happo Ridge during the intensive period from 15 May to 11 June in Simulated concentrations of (c) anthropogenic sulfate in mg m 3 at 0000 LST on 26 May and (d) volcanic sulfate at 0400 LST on 30 May with wind patterns around Japan at about 1500 m MSL. at the same height of Figure 7c at 0400 LST on 30 May. Southeasterly wind in high pressure system on the northwest Pacific Ocean carried the volcanic sulfate to Happo Ridge and 95.5% of total sulfate was the volcanic sulfate at that time. Thus those high sulfate concentration episodes observed at Happo Ridge were clearly classified into the continental origin and Miyakejima origin quantitatively. [22] In terms of sulfur dioxide concentration, no peak was seen during the continental event. However, sulfur dioxide concentration was high during the Miyakejima event. As a result of relatively short distance between Happo Ridge and Miyakejima Volcano (300 km) compared to the distance to the continent (several thousands of kilometers), sulfur dioxide in the volcanic plume was not converted to sulfate adequately. Therefore the ratio of sulfur dioxide to sulfate can indicate the origins of high sulfate concentration episodes [S-04] Gas-Aerosol Equilibrium of Ammonia [23] S-04 classified the origin of plume which brought high sulfate concentration episode to Happo Ridge into anthropogenic origin and volcanic origin using backward trajectory analysis during the intensive period of Figure 3c, from September to October According to the result, anthropogenic plume contained 3 mg m 3 of sulfate on average and 75% of total ammonia was existing in aerosol phase. In contrast, 17 mg m 3 of sulfate was found in the volcanic plume and the superabundant sulfate fixed 100% of ammonia into aerosol phase and excessive sulfate became sulfric acid mist and aerosol was strongly acidified. [24] Figure 8 shows temporal variations of ammonia and ammonium concentrations at Happo Ridge from 1600 LST on 23 May to 0000 LST on 1 June in 2001 including the two episodes discussed in the previous section. Boxes indicate observed particulate ammonia, solid line with closed circles is simulated particulate ammonia, solid line without circles is simulated particulate ammonia without eruption of Miyakejima Volcano and dashed line is simulated total ammonia (gas plus aerosol). During the period, MSSP simulated transport and gas-aerosol partitioning of ammonia very well and the correlation coefficient was R = [25] As discussed in section 4.2, two characteristic episodes were observed on 26 and 30 May Uematsu et al. [2004] carried out atmospheric observation on selfcruising boat and indicated that Miyakejima Volcano has emitted substantial amount of ammonia, which is estimated 8of11

9 Figure 8. Temporal variations of ammonia and ammonium concentrations at Happo Ridge from 1600 LST on 23 May to 0000 LST on 1 June in Boxes denote measured particulate ammonia, solid line with circles is simulated particulate ammonia, and solid line without circles is simulated particulate ammonia in case of no eruption. Dashed line denotes simulated total (gas plus aerosol) ammonia. as 0.34 TgN yr 1, as well as sulfur dioxide. Since the ammonia emission is still uncertain, all kinds of ammonia emission considered in this study are related to human and animal activities (animals, fertilizer, biofuel use and biomass burning), which is 22.0 TgN yr 1 [Streets et al., 2003], and no volcanic emission was included. Ammonium ion concentration became also high during both episodes. However, in terms of total ammonia itself, the continental air mass containing abundant sulfate ammonium passed Happo Ridge on 26, while high ammonia concentration episode was not found on 30. The measured high concentration of ammonium ion at Happo Ridge on 30 was quantatively explained by gas to particle conversion of ammonia gas caused by volcanic sulfate increase, excluding the volcanic ammonia emission. During the continental episode from 2000 on 26 to 2000 on 27, 63.5% of ammonia existed in aerosol phase. In contrast, when the volcanic plume reached to Happo Ridge from 2000 on 29 to 2000 on 30, 100% of ammonia was fixed into aerosol phase and only 27.7% would have been in aerosol phase in case if no volcanic sulfur emission occurred. The volcanic sulfate fixed ammonia gas into aerosol phase as ammonium by 5.1 times compared to the case of no volcanic sulfur emission during the episode Precipitation Acidification [26] Sulfur dioxide emitted from Miyakejima Volcano were acidified and converted to sulfate in liquid phase and in the air. The volcanic sulfate increased over far east Asia caused acidification of precipitation. Simulation results of annual mean ph value and ph decrease caused by the volcanic sulfate are shown in Figures 9a and 9b, respectively. Annual mean ph value of precipitation over Japan is within a range between 4.5 and 5.0 [Wang et al., 2002]. MSSP simulation is also within the same range. Monthly mean ph of precipitation at Happo Ridge was simulated fairly well (R = 0.52). S-04 compared annual mean ph decrease of precipitation before and after the eruption and found that ph decreased from 4.98 to 4.92 (D = 0.06). The 2-month average of precipitation acidity just after the eruption on August and September 2000 was The value was lower by 0.45 compared to the average value on the same months in the previous year, August and September 1999, that was According to the simulation shown in Figure 9b, ph value decreased by 0.1 to 0.3 in the area along Japan Sea and 0.3 to 1.0 along the Pacific Ocean on annual average from September 2000 to August [27] Asian dust particles, deflated from large deserts in western and northwestern parts of China, so-called yellow sand, has been neutralizing east Asian atmospheric environment. Several numerical and observational studies have done on this topic [Wang et al., 2002; Terada et al., 2002]. Wang et al. [2002] calculated that the neutralization effects can increase ph values by in Japan, in Korea, and more than 2 in northern China during spring, the most influential season. The acidification of precipitation caused by the eruption of Miyakejima Volcano was equivalent to the neutralization by yellow sand in Japan. 5. Conclusions [28] A regional-scale Eulerian Model System for Soluble Particles (MSSP) was constructed to simulate environmental changes caused by sulfate increase as the result of the eruption of Miyakejima Volcano, located in the northwest Pacific Ocean and 180 km south from Tokyo metropolitan area, which has begun to erupt since July 2000 and been emitting huge amount of sulfur dioxide to present. Japan Meteorological Agency measured sulfur dioxide emission by COSPEC (correlation spectrometer) continuously since September According to the measurement, the volcanic emission was 9 Tg yr 1 on annual average, equivalent to 70% of global volcanic emission and 6.9% of global emission from anthropogenic sources. Seasonal variations of the volcanic sulfate increase, change of gas-aerosol partitioning of ammonia and ph decrease of precipitation were studied using the MSSP model for 1 year from the beginning of COSPEC measurement in September 2000 to August 2001, together with observation performed at Happo Ridge observatory in mountainous area in central Japan [Satsumabayashi et al., 2004; S-04]. [29] Volcanic sulfate dispersed variously by season. At Happo Ridge, annual mean sulfate concentration was 3.83 mg m 3, 1.5 times larger than that before the eruption, and the volcanic sulfate contribution to total sulfate was 9of11

10 Figure 9. Simulated annual mean (a) ph value of precipitation and (b) ph decrease caused by the eruption of Miyakejima Volcano. 46%. The volcanic sulfate concentrations were predominant in May, October and August and the contributions were 84.0%, 61.1% and 52.4%, respectively. However, the volcanic influence was less in February, December and June, and the percentages were 11.9%, 13.4% and 22.7%, respectively. In winter season northwesterly wind is prevailing around Japan and volcanic sulfate was mainly transported southeastward to the Pacific Ocean. Monthly mean volcanic sulfate concentration in winter in Japan was very small (almost 0 mg m 3 ), while the fraction of volcanic sulfate was larger (more than 50% in large area) in the Pacific Ocean than other months in the year. In contrast, in summer due to the subtropical high-pressure system over the Pacific Ocean, volcanic sulfate was transported westward and southwestward and reached to Korea and southwestern Japan. The volcanic sulfate concentration was mg m 3 in Japan, more than 1 mg m 3 in Korea and 2 mg m 3 in Taiwan. The volcanic sulfate concentration became high in August 2001 although sulfur dioxide emission from the volcano has decreased with time. [30] Temporal variations of sulfate concentration and gasaerosol equilibrium of ammonia at Happo Ridge were well simulated during an intensive observation period from May to June Two high sulfate concentration episodes were clearly classified into the continental (anthropogenic) origin and Miyakejima origin by the model. During the continental event, 98.7% of total sulfate was anthropogenic and 63.5% of ammonia existed in aerosol phase as ammonium sulfate. In contrast, in the volcanic plume 95.5% of total sulfate was volcanic and excessive sulfate fixed 100% of ammonia into aerosol phase by 5.1 times compared to the case if no volcanic sulfur emission occurred and aerosol was strongly acidified during the episode. [31] Acidification of precipitation caused by volcanic sulfate increase was simulated by MSSP. Annual mean ph of precipitation decreased by 0.1 to 0.3 in the area along Japan Sea and 0.3 to 1.0 along the Pacific Ocean, which was equivalent to neutralization by yellow sand in Japan. [32] Acknowledgments. The authors wish to thank T. Kanno at Japan Meteorological Agency for providing data sets of measured emission from Miyakejima Volcano. We also feel obliged to K. Matsuda and A. Aoyagi at Acid Deposition and Oxidant Research Center who provided monitoring data sets of EANET. We would like to thank D. Streets at Argonne National Laboratory for providing emission inventory data in east Asia. This study was supported by funds from the Grant-in-Aid for Scientific Research on Priority Areas under grant from Ministry of Education, Culture, Sports, Science and Technology, in Japan. References Albrecht, B. A. (1989), Aerosols, cloud microphysics, and fractional cloudiness, Sience, 245, Allard, P. (1997), Endogenous magma degassing and storage at Mount Etna, Geophys. Res. Lett., 24(17), An, J., H. Ueda, Z. Wang, K. Matsuda, M. Kajino, and X. Cheng (2002), Simulations of monthly mean nitrate concentrations in precipitation over east Asia, Atmos. Environ., 36, Andres, R. J., and A. D. Kasgnoc (1998), A time-averaged inventory of subaerial volcanic sulfur emissions, J. Geophys. Res., 103(D19), 25,251 25,261. Benkovitz, C. M., M. T. Scholtz, J. Pacyna, L. Tarrason, J. Dignon, E. C. Voldner, P. A. Spiro, J. A. Logen, and T. E. Graedel (1996), Global gridded inventories of anthropogenic emissions of sulfur and nitrogen, J. Geophys. Res., 101(D22), 29,239 29,253. Carmichael, G. R., et al. (2002), The MICS-Asia study: Model intercomparison of long-range transport and sulfur deposition in east Asia, Atmos. Environ., 36, Chameides, W. L. (1984), The photochemistry of a marine stratiform cloud, J. Geophys. Res., 89, Chameides, W. L., and D. D. Davis (1982), The free radical chemistry of cloud droplets and impact upon the composition of rain, J. Geophys. Res., 87, Dudhia, J. (1993), A nonhydrostatic version of the Penn State/NCAR mesoscale model: Validation tests and simulation of an Atlantic cyclone and cold front, Mon. Weather Rev., 121, Fujita, S., T. Sakurai, and K. Matsuda (2003), Wet and dry deposition of sulfur associated with the eruption of Miyakejima volcano, Japan, J. Geophys. Res., 108(D15), 4444, doi: /2002jd Grell, G. A. (1993), Prognostic evaluation of assumptions used by cumulus parameterizations, Mon. Weather Rev., 121, of 11

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