A sag in the ozone layer over the Qinghai-Tibet Plateau that has caught the attention of the world. Experts have warned that if this sagging phenomenon persists, the holes in the ozone layer over the north and south poles will increase to include a third over the roof of the world.

For over 200 days Chinese and Japanese scientists have conducted a joint investigation, and collected large amounts of first-hand materials concerning the sagging ozone layer. They are currently processing and analyzing this data in the hopes of finding an explanation for the sag.
The scientific investigation, initiated in June 1998, is a cooperative project between the China Natural Science Fund and the Chinese and Japanese governments. According to Shi Guangyu, the chief scientist on the Chinese side of the project and a research fellow from the Institute of Atmospheric Physics under the Chinese Academy of Sciences, until all the data have been processed and analyzed, no conclusions can be drawn as to identifying the factors contributing to the formation of the sag. The whole process will take some time.
Affecting the Ecology in Tibet
In the summer of 1996 Chinese scientists, represented by Zhou Xiuji, an academician of the Chinese Academy of Sciences, first discovered the low point in the ozone layer over the Qinghai-Tibet Plateau, by means of ground observation material and through analyzing the American meteorological satellite data. Since then the question of whether a third hole will appear in the ozone layer has become the focus of worldwide attention. International environmental protec6tion organizations, composed mainly of executive members of the Multilateral Fund of the UN Montreal Convention, have commenced investigations and assessment in Tibet.
Ozone is a molecule composed of three oxygen atoms. The ozone layer within the atmosphere can be as close as 30 kilometers from the earth's surface, and its function is to block harmful ultraviolet rays from the sun. It has been described as a "protective umbrella" for the earth. Unfortunately, the ozone layer has been severely damaged in recent years due to excessive use of freon, causing ozone holes to appear over the north and south poles.
It has been proved that a low ozone phenomenon has occurred above the Qinghai-Tibet Plateau, resulting in large amounts of 'unfiltered" ultraviolet rays, which could be the cause of the sharp increase in cataract cases and other diseases among inhabitants of the plateau, variations within local plant and animal species, the acceleration of melting of glaciers, and other ecological damage.
According to an environment investigation report published by the Tibetan Autonomous Regional Government, the temperature has, in recent years, increased in most parts of Tibet. The thin ozone layer has caused a high proportion of exposure to ultraviolet rays. The situation is exacerbated by snow and rocks having a strong reflective capacity for ultraviolet rays. Consequently, occurrences of cataracts on the plateau have increased year by year, to the extent that the area has the highest incidence in China. The age of such occurrence is also five to ten years younger than that in flat areas.
In recent years the glaciers on the plateau have shown a tendency to thaw faster, resulting in an increase in vaporization and rainfall. In the flooding season, the water level of rivers rises sharply, causing serious soil erosion. Meanwhile, the water level of alpine lakes has lowered, causing soil desiccation of varying degrees in the valleys and around the lakes.
Though no accurate quantitative and qualitative analysis has been made of the damage to wild animals and plants in Tibet caused by the increasing amount of proven that the snow line in northern Tibet has risen by 100-150 meters, which may have caused changes in the areas inhabited by animals around the snow line, and consequently to their eating and living habits, reproductive rhythms and general living conditions.
Fortunately, most areas on the Qinghai-Tibet Plateau have maintained their natural ecological environment. Most of the 1,500 large and small lakes on the plateau are at their protogenic stage. Forests cover 7.17 million hectares, and grassland, 130 million hectares. At present, Tibet has 13 nature reserves which are classified as above provincial level, and 39 wild plant and 125 wild animal species have been placed under state protection. Moreover, the area has negligible industrial pollution.
Sino-Japanese Joint Efforts
Since 1998 the Institute of Atmospheric Physics under the Chinese Academy of Sciences has cooperated with the institute of the Sun and Earth Environment attached to Japan's Nagoya University in conducting high-altitude exploration, using balloons, and an aerosol survey by laser radar. According to Shi Guangyu, few areas of the world have conducted synchronized surveys of the vertical distribution of ozone and aerosol, and this is the first time such a survey has ever been carried out on the plateau. The cost of an ozone explorer is over 10,000 yuan, while that of an aerosol explorer is more than 100,000 yuan, and, since they are irretrievable, they can be used only once. For this reason, these scientists cannot conduct such surveys very often.
To conduct comparative studies and thereby reduce costs, Shi and his people cooperated with the Chinese Institutes of Meteorological Science and made an ozone survey by means of ground brewer spectrophotometers and an aerosol survey by means of laser radar that is capable of reaching an altitude of 30,000 meters. Over a period of 220 days, they obtained nearly 100 batches of laser radar data. Meanwhile, they made 22 ozone explorations, three aerosol explorations and carried out joint studies of basic meteorological elements, such as terrestrial sun radiation, aerosol particle spectrum, black carbon aerosol, ozone on the ground surface, sulfur dioxide and nitrogenous oxide.
According to Shi Guangyu, a basic analysis of this data indicates that the plateau is exposed to a high degree of sun radiation in summer and is therefore a source of heat. Above the plateau there is a strong rising airflow. Ozone is thin on the top of the troposphere at the altitude of 15 kilometers above Lhasa; the divided voltage of ozone is the highest at the altitude of 25 kilometers; and at the altitude of 30-40 kilometers, the proportional mixture is the highest.
From June to October, the total amount of ozone above the plateau is at least 10 percent less than that of areas to its east at the same latitude. However, with increasing governmental attention and concern directed towards protecting the ozone layer, the ozone loss over the plateau is expected to slow down. Based on the available data and the perceptible development trend, Shi believes that lost ozone is likely to be recovered within 50 years and no hole will form in the ozone above the plateau.
Ozone Sagging needs More Study
Some experts suggest that apart from industrial discharge, dynamic and thermodynamic functions are also major culprits as regards the sagging of the ozone layer over the Qinghai-Tibet Plateau. in summer, the plateau is the richest source of heat emanating out to the atmosphere. The atmosphere at an altitude of 18 kilometers and lower is subject to a strong upward vertical airflow, lifting the lower air that contains less ozone and thereby diluting ozone at a higher altitude. They cited the huge thermal and dynamic power generated by air circulation as the cause of ozone loss above the Rocky Mountains, the Andes and the Alps.
Shi concedes that this theory might explain one of the reasons, but does not consider that it can accurately reflect the whole situation, because it cannot explain why ozone over the plateau has consistently decreased since 1979, while there is no concurrent evidence of an increased upward airflow. He points our that the ozone sag over the plateau might be a completely different phenomenon from the decrease of ozone over the north and south poles. The latter is mainly caused by a chemical process, while the former might be caused by a mixture of dynamic and chemical processes, most likely a non-homogeneous chemical process related to aerosol, as the current data indicate a high content of aerosol at the altitude between 15 and 25 kilometers above Lhasa.
Shi says the first-hand data from the aerosol survey and the laser radar observation of ozone and aerosol have great scientific significance to the study of the ozone sag over the plateau. the data can give an explanation as to how the dynamic and chemical processes function to create the sag in the ozone layer over the plateau, as well as providing material for a comparative study of the ozone decrease in the north and south poles. The data are also very important to the study of global ozone changes and their effects on the climate and environment.