生产率高，质量好，无渣，明弧，能见度高；
Work in high efficiency with good welding quality. No slag, opened arc and high visibility;
1981年为大气能见度变化的转折期，在此期间11个城市的能见度迅速降低、“非常好”能见度出现频率很快下降。
The turning period of visibility change took place during 1979-1981, and both the visibility and "very good visibility" frequency of the 11 cities decreased rapidly at that time.
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