Acid Deposition
Air pollutants emitted from East Asian countries in the midst of rapid economic development are transported over great distances. They arrive in Japan as acid rain. Using both aircraft and ground-based observation stations, NIES continues to observe the behavior of air pollutants (geographical distribution, seasonal changes, etc.) from the Asian continent and is studying acidic substances that have been absorbed in rain and snow.
NIES has monitored atmospheric gases and aerosols on the Goto Islands
in Nagasaki Prefecture (northern Kyushu) and Dazaifu City (Fukuoka Prefecture)
during the winter, when the strong prevailing winds blow from the northwest.
Researchers confirmed that both locations experience high concentrations
of sulfates that appear to originate mostly from continental sources,
and that the pollution belt was more than 200 km wide. Aircraft observations
later confirmed the pattern of air transported from the Asian continent.
Patterns of air mass movement from the Asian continent
Air from the northeastern part of Russia (A) is relatively clean, since
it has few major pollution sources. On the other hand air from northern
China (B) contains a large amount of acidic substances. Air that passes
over the Korean Peninsula (C) before reaching Japan contains pollutants
that have not yet been oxidized as it is still near the pollution source.
Observations led to a more robust explanation for the large-scale transport
of polluted air from the continent: It occurs when high or low atmospheric
pressure systems move past Japan, not only when the prevailing winds blow
from the northwest in winter (D). Aircraft observations confirmed the
presence of high concentrations of air pollutants at both low and high
altitudes when these pressure systems passed, due to large movements of
air masses and active vertical mixing.
Computer simulation models and graphics show visually how air pollutants
emitted in the southern part of China are transported to the central part
of Japan after traveling northward briefly and then southward again.
Transport of air pollutants
emitted in southern China to the central part of Japan. Data from 13 to
15 January 1997. (Jointly developed with Kyushu University, Research Institute
for Applied Mechanics)
In addition, during the "baiu" early summer rainy season in Japan, air pollutants originating from continental China and the Korean peninsula arrive at the northern part of Kyushu at the north edge of the rainy season front, along Japan's southern coast. The pollutants undergo repeated chemical reactions and changes as they travel long distances.
Other work by NIES includes research to predict future amounts and sources
of acid deposition-causing substances. It became clear that in China,
combustion accounts for about 90 percent of hydrocarbon emissions (a source
of ozone generation) and coal-burning accounts for more than half of all
combustion.
In order to study the effects of acid deposition on ecosystems, NIES conducts
field studies on Yakushima Island, famous as a World Heritage Site. The
entire island is composed of granite, which is poor in nutrients. In addition,
the river water in Yakushima has weak ability to neutralize acid. Research
confirmed that the island was very susceptible to the effects of acid
precipitation, which contains high amounts of sulfuric acid.
Study of pH and acid
buffering capacity of surface water in watersheds
This shows that rivers of Yakushima are relatively more vulnerable to
acidity than other areas in Japan.
Ecosystems of the island-dominated by forest and river ecosystems-survived until recently without being affected by anthropogenic pollution. However, the effects of eutrophication from nitrogen compounds such as nitric acid and ammonia have raised considerable concern in recent years, as a result of acidic substances falling and settling at high altitudes on steep mountain slopes.
