二氧化硫熏气处理后对蚕豆（Ｖｉｃｉａ ｆａｂａ Ｌ．）叶片的伤害可划为３种类型，即不可见伤害、可逆的可见伤害以及不可逆伤害。采用动态熏气的方法初步估计了３类伤害的阈值，不可见伤害阈值小于131.2μｇ／ｍ^３×８ｈｓ，可见伤害阈值为1322.8μｇ／ｍ^３×２ｈｓ，1322.8μｇ／ｍ^３ＳＯ_２处理时不可逆伤害阈值介于１６ｈｓ（累积小时数，下同）和２４ｈｓ之间，而以７７５．０μｇ／ｍ^３ＳＯ_２处理时，则介于３２ｈｓ和４０ｈｓ之间。认为超氧化物歧化酶活性作为不可见伤害和不可逆伤害的指标较为适宜，可见伤害阈值则可沿用传统的５％伤害叶面积作指标。

There are three injury types of the leaves of Vicia faba  L. when fumigated with different doses of SO₂, i. e. , invisible injury, visible injury (recoverable) and unrecoverable injury. The threshold values of the three types of injury estimated by dynamic fumigation experiments are less than 131. 2μg/m³ SO₂× 8 hs for invisible injury, 1322. 8 μg/ m³ SO₂ ×2 hs for visible injury and 1322. 8 μg/m³ SO₂ × 16～24 hs (accumulated) or 775. 0μg/m² SO₂ × 32～40 hs for unrecoverable injury. It is suggested that 5% injuried leaf area is suitable for the index of visible injury. Superoxide dismutase activity can be used as the index of the invisible injury and unrecoverable injury for it is sensitive to SO₂ and changes dramatically with the increase of SO₂ dose.