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We have investigated the effects of SO₂ and NO₂ on visible injury, stomatal opening and the activity of photosynthesis in 10 foliage plants. And also in order to determine the air purification ability of plants, the accumulation of water soluble sulfur in leaves and the NO₂ fixation rate were examined. The degrees of injury by SO₂ and NO₂ can be. divided into three types; Monstera deliciosa belongs to sensitive species, Ficus benzamina and Scindapsus aureus to middle species and Rhapis excelsa to tolerance species. The threshold concentration showing visible injury was more than 0.4 ppm SO₂ and 1.0 ppm NO₂ in sensitive plants. In addition, degrees of damage to plants caused by NO₂ were lower than those by SO₂. The diffusion resistance of 3 foliage plants increased by increasing SO₂ concentration, but it did not showed any difference in NOz fumigation. The photosynthetic activity tended to decrease by increasing SOz and NO₂ concentration, but it increased at concentration of 0.5 ppm NO₂. These facts showed that low concentration of NO₂ acted as nutrition source to plants, and NO2 is easier than SO₂ to be absorbed by foliage plants. Gas absorption rate of 4 foliage plants increased in optimal concentration which didn´t show physiological injury : since accumulation of sulfur contents has increased in SO₂ treatment leaves and also 3-4.5 ㎎·m^(-2)·h^(-1) in NO₂, it can be used to purify indoor air. On the other hand, we found that tolerance species such as Rhapis excelsa is working more effectively in heavy polluted indoor than sensitive species.
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