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本世纪初叶加拿大和美国部分地区森林苗木上有些不常见的病害就已归因于本地区工业生产所发出的气体。今天,空气污染的急性和慢性两种状态对森林苗木的安全更具有严重的威胁。臭氧、氟化物和二氧化硫这三种主要危险物质目前可能越来越广泛了,它们是导致苗木严重疾病的因素。还有从现代化技术所造成的新的污染的化学形成物与气流中微小污染粒子结合,也给苗木带来更多的毒性。臭氧(O_3)臭氧是都市近郊所形成的化学烟雾中的主要组成物。在北美温带地区,这种氧化物比较其他污染物给植物带来的灾难更多些。
Some of the less common diseases on forest seedlings in Canada and parts of the United States at the beginning of this century have been attributed to the gases emitted by industrial production in the region. Today, both acute and chronic air pollution pose a more serious threat to the safety of forest seedlings. The three major hazardous substances, ozone, fluoride and sulfur dioxide, are likely to become more widespread at this time and they are contributing to serious diseases of seedlings. There are also new contaminated chemical forms that result from modern technology combined with tiny particles of contaminants in the air stream, which also give the seedlings more toxicity. Ozone (O_3) Ozone is a major component of chemical fumes formed in the suburbs of cities. In temperate North America, this oxide gives plants more disasters than other pollutants.