Mizuo Kajino

Enhancement of primary productivity in the western North Pacific caused by the eruption of the Miyake-jima Volcano

[1]xa0The eruption of the Miyake-jima Volcano (34.08°N, 139.53°E) in the Izu Islands, Japan, 180 km SSW of Tokyo, began on 8 July 2000. A substantial amount of NH3 gas was found to be emitted from the Miyake-jima Volcano together with SO2 gas and that geochemically significant quantities of aerosol particles composed of ammonium sulfate form in the plume. Through the use of satellite images, the additional atmospheric deposition of ammonium sulfate caused an increase of phyto-plankton in the nutrient-deficient region south of the Kuroshio. The emission of volcanic gases from the Miyake-jima has likely been modifying the marine air quality as well as the open ocean ecosystem over parts of the western North Pacific for the past several years.

Simulations of monthly mean nitrate concentrations in precipitation over East Asia

Abstract Monthly mean nitrate concentrations in precipitation over East Asia (10–55°N, 75–155°E) in April, July, September, and December of 1999 were simulated by using a regional air quality Eulerian model (RAQM) with meteorological fields four times per day taken from National Centers for Environmental Prediction. The distribution of the nitrate concentration in precipitation depends significantly on the emission patterns of nitrogen oxides (NOx=NO+NO2) and volatile organic compound (VOC) and seasonal precipitation variability. The downward trend is also revealed, particularly in July and December. Highest concentrations are found in the industrialized regions, i.e., the coastal area of the Mainland of China, the Bay of the Huanghai Sea and the Bohai Sea, Korea, and Southern Japan. Long-range transport may cause elevated concentrations in remote areas downwind of the industrialized regions under favorable meteorological conditions, e.g., low precipitation. Comparison of observations and simulations indicates that the RAQM model reasonably predicts synoptic-scale changes in different months (seasons) and simulated nitrate levels in 4 months fit observed data with the discrepancy within a factor of 2. Exclusion of liquid chemistry within clouds is feasible for regional (1°×1°) and long-term (monthly) nitrate simulations. The uncertainty originates mainly from that of the emission data and modeled precipitation amounts and initial and boundary conditions.

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

[1]xa0A regional-scale Eulerian Model System for Soluble Particles (MSSP) was constructed to simulate environmental changes caused by a SO42− increase as the result of the eruption of Miyakejima Volcano in the northwest Pacific Ocean. The measured volcanic SO2 emission was 9 Tg yr−1 for a year from the beginning of the eruption, July 2000. 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 NH3 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 SO42− was mainly transported southeastward to the Pacific Ocean while volcanic SO42− was transported southwestward to Japan, Korea, and Taiwan, owing to the subtropical high-pressure system over the Pacific Ocean in summer. Temporal variations of SO42− concentrations and gas-aerosol equilibrium of NH3 at Happo Ridge were well-simulated. In the plume from the Asian continent, 98.7% of total SO42− was anthropogenic, and 63.5% of NH3 existed in aerosol phase as (NH4)2SO4. In the volcanic plume, 95.5% was volcanic, excessive sulfate fixed 100% of NH3 into aerosol phase, and aerosol was strongly acidified. Modeled annual mean pH of precipitation in Japan decreased by 0.3–1.0, which is equivalent to neutralization by yellow sand.

Effects of Miyake volcanic effluents on airborne particles and precipitation in central Japan

Miyakejima volcano began to erupt from 8 July 2000 which is located in the Northwest Pacific Ocean and 200 km south from Tokyo Metropolitan area. Its SO 2 emission amounted to a maximum 6 x 10 4 ton/day which was about the same level as the anthropogenic emission of China (54,800 ton/day) and twenty times larger than Japanese one (3,120 ton/day), and is decreasing to 10 4 ton/day. Aerosol and precipitation, together with gaseous pollutants have been observed from two years before the eruption to present on a prominent mountain ridge, Happo ridge (1850m ASL and 330 km north from the volcano), presuming them to be representative of the mid-troposphere air quality over central Japan. Short time sampling of aerosols was made for three hours every day, while four-hours sampling was done consecutively in the intensive observation periods. One-day collection was made for precipitation and every one-hour monitoring was done for SO 2 , NO, NO 2 and O 3 , and PM10. Water-soluble inorganic species, Na + , K + , Mg 2+ , Ca 2+ , NH + 4, SO 2- 4, NO - 3, Cl - in the aerosol and precipitation were analyzed. Annual mean concentration of SO 2 was increased 3.8 times and those of SO 2- 4 were 1.5 and 1.6 times in aerosol and precipitation. Because of the excess amount of SO 2- 4 formation, driving out NO - 3 and Cl-, it took their place in the aerosol, and sometimes existed as sulfuric acid mist after exhausting ammonium gas. It makes the aerosol at pH values less than 1 and partitioned into SO 2- 4 and HSO - 4. These facts were explained successfully by a multi-component gas-aerosol equilibrium.

Increase in nitrate and chloride deposition in east Asia due to increased sulfate associated with the eruption of Miyakejima Volcano

[1]xa0The eruption of Miyakejima Volcano, 180 km south of Tokyo, Japan, since July 2000 has resulted in the emission of large amounts of sulfur dioxide. The volumes of sulfur dioxide emitted were vast, equivalent to half the anthropogenic emission from China on annual average. Short-time aerosol sampling, conducted at the Happo Ridge observatory in the central mountainous region of Japan, has revealed that the abundant volcanic sulfate resulted in the expulsion of nonvolcanic nitrate and chloride in aerosols into the gas phase. As the deposition velocities of gaseous nitrate and chloride are much higher than those in aerosols, their deposition should be accelerated. This additional deposition is referred to as “indirect acidification” in this study, corresponding to “direct acidification” by the deposition of volcanic sulfate. This indirect acidification is estimated quantitatively using a regional-scale Eulerian aerosol transport model and is found to be generally less pronounced than direct acidification, although the indirect effect was 2.1 greater than the direct effect over the North Pacific Ocean in winter. The minimum contribution of indirect acidification is found to be 7%, which is still not negligible. Indirect acidification may also occur in the case of general air pollution, accelerating the acid deposition of nitrate and chloride in sulfate-rich contaminated air masses. It therefore appears to be important in general to consider indirect acidification in the discussion of environmental acidification by sulfur oxides.