July 31, 2003
The Ministry of the Environment has compiled the results of ozone layer monitoring, covering the FY 2002 status of (i) ozone depletion, (ii) atmospheric chlorofluorocarbons (CFCs) concentrations, and (iii) solar ultraviolet radiation, pursuant to Article 22, Para.2 of the Law concerning the Protection of the Ozone Layer through the Control of Specified Substances and Other Measures (hereinafter referred to as "Ozone Layer Protection Law") *1
The stratospheric temperatures over Antarctica in 2003 remain at the lowest range since the 1980s, when the ozone hole first became noticeable. Large amounts of Polar Stratospheric Clouds (PSCs) have occurred since late May because of the low temperatures. These clouds are believed to play a central role in the formation of the ozone hole. Observation results confirmed that about 30% of ozone has already been destroyed over Antarctica as of the end of August 2003. This is the worst ever ozone depletion that has occurred at this time of the year. The ozone hole over Antarctica is expected to become even larger in the coming months of September and October.
The main contents of the report are as follows:
1. State of the ozone layer
Total ozone shows a continuous downward trend in the long term except at low latitudes. A marked decline is notable in the spring at high latitudes. In Japan, a long-term decline is also evident at three locations, with Sapporo showing the most prominent decrease. The sole exception to locations showing decline is the Naha location.
In 2002, the maximum area of the ozone hole over Antarctica was the smallest observed since 1991. The ozone hole transformed and broke up, making its earliest disappearance since 1989. The total ozone measured above the Showa Base has been found to be below 220m atm-cm-the figure required to be regarded as an ozone hole-since mid-August. It then fluctuated substantially until mid-September and remained at a low level during late September. It edged up beginning in mid-October. The monthly average for October was the highest in the last twenty years. In November and December, total ozone also reached the second highest levels. Although the size of the ozone hole became smaller in 2002, it was the result of anomalous climate conditions; it could not be interpreted as an indication of recovery of ozone. ( Fig. 1)
Compared to the reference values (1971-2000 average, and 1974-2000 average for Naha), the total ozone in midair above Japan in 2002 was at a low level at Sapporo in the months of January, April, and May; at Tsukuba in the months of February, March, and July; and at Kagoshima in the months of January and July. On the other hand, high levels were observed at Tsukuba in the months of June, September, November, and December; at Kagoshima in the months of October and November; and at Naha from September to December. In particular, the lowest level recorded since the start of observation was at Tsukuba in July, and the highest level recorded since the start of observation was in October and December at Naha. (Fig.2)
Depletion of the ozone layer on a global scale cannot be explained by any known natural phenomenon. Increase in the concentrations of CFCs in the air is believed to be the main cause. Growth of the ozone hole over Antarctica after the 1980s, in particular, is most likely to be the result of increased concentrations of CFCs in the air.
The Scientific Assessment Panel of the Montreal Protocol pointed out the following in its report, Scientific Assessment of Ozone Depletion: 2002, published under the auspices of the World Meteorological Organization (WMO) and United Nations Environment Programme (UNEP):
|(i)||According to stratospheric observation, total chlorine has peaked or nearly peaked while the concentration of bromine still seems to be on the rise;|
|(ii)||Chemical/climate models predict that if halogen in the stratosphere decreases as anticipated, springtime ozone layer over Antarctica will begin to increase by 2010.|
|(iii)||As observation data accumulate, the decrease in total ozone is being confirmed as leading to an increase in the amount of UV radiation reaching the Earth's surface.|
2. State of atmospheric CFCs concentrations
At the observation site in Hokkaido, which represents the typical conditions at mid-latitudes in the northern hemisphere, the concentration of CFC-12 has shown little change since the latter half of the 1990s, and the concentrations of CFC-11 and -113 are in decline. 1,1,1-trichloroethane, which has a short life in the air, already shows a declining trend. (Fig.3)
The concentrations of CFC-11, -12, -113, 1,1,1-trichloroethane, and carbon tetrachloride in the air measured in Kawasaki City, as an indication of the situation in urban areas, showed that the concentration levels of these substances are gradually approaching those in Hokkaido. It is believed to be the result of regulations implemented in accordance with the Montreal Protocol since July 1989. On the other hand, the rising trends of halogen 1211 and 1301 continue. The concentrations of CFC substitutes in the atmosphere in Hokkaido, including HCFC-22, -141b, -142b, and HFC-134a, are also on rise.
Compared to the 1970s, for instance, when the ozone hole over Antarctica was not yet identified, the concentrations of specified substances in the atmosphere today are at substantially high levels. In order to improve the condition of the ozone layer in the stratosphere, concentrations of these substances need to be drastically reduced.
3. State of solar ultraviolet radiation reaching the Earth's surface
Assuming the premise that the dosage of harmful ultraviolet rays (UV-B) reaching the earth increases with the depletion of the ozone layer, incidences of skin cancer, cataracts, immunosuppression and other effects on human health are anticipated to increase. Adverse effects on terrestrial and aquatic ecosystems and aggravation of air pollution are also possible results of increased UV-B rays. It is important therefore to monitor changes in the quantity of UV-B reaching the surface of the planet.
While accumulation of data should be continued, UV-B measurements obtained at four locations in Japan have not shown any trend of huge changes since Japan began observation in 1991. Ultraviolet rays with a wavelength of 300 nm, which are sensitive to changes in total ozone, also have not shown any obvious trend. However, besides total ozone, it is necessary to note that the UV-B measurements obtained from observation is susceptible to influences of climate (cloudiness) and murkiness of the air. According to analyses conducted by the Meteorological Agency, based on the results obtained from observation of the total ozone and the quantity of UV-B on sunny days at four locations in Japan thus far, if the sun is at the same altitude angle, it has been confirmed that the UV-B dosage on the ground will increase when total ozone decreases. Therefore, it is conceivable that the quantities of UV-B reaching the surface have increased in areas where total ozone has clearly decreased as compared to the 1970s. (Fig. 4)
|Notes:||1.||Article 22 of the Ozone Layer Protection Law reads:
The Director General of the Meteorological Agency shall monitor the state of the ozone layer and the atmospheric concentrations of specified substances and publish the obtained results.
2. Utilizing the obtained results in Paragraph 1, the Minister of the Environment shall monitor the state of the ozone layer depletion due to specified substances and the fluctuations of atmospheric concentrations of specified substances, and to subsequently publish the obtained results.
|2.||The Scientific Assessment Panel and the Environmental Effects Assessment Panel under the Montreal Protocol have each, for the first time in four years, put together a report in 2002. The Ministry of the Environment referred to these reports in preparing the FY 2002 Annual Report of Ozone Layer Monitoring Results. Gist of the panels' reports are given below.
(i)Scientific Assessment of Ozone Depletion: 2002