1991～1993年在河北省承德市5个大气监测点测定8种常见绿化树种树皮pH值的变化，结果表明8种树皮pH值为3.5～7.0，平均值为5.7±0.6。不同功能区树皮pH从大到小依次为：公园区＞工业区＞生活居住区（P＜0.05），与大气SO₂等酸性气体的污染有关。同种植物的树皮浸提液SO_4^2-含量相对清洁区为2.516mg／g，污染区为5.342mg／g（P＜0.001），两者之间的相关公式为Y＝2.576＋6.4736X（r＝0.7730，P＜0.001）。树皮pH与SO_4^2-呈极显著负相关，相关公式为Y＝7.1－0.3865X（r＝－0.8941，P＜0.001）。榆树等4种落叶阔叶树树皮对大气SO₂的变化较敏感，可作为SO₂等酸性气体的适宜指示与监测植物。

The pH values of the barks of 8 tree species changed from 3.5 to 7.0, with average value being 5.7 ±0.6, and were lower than that of naturaly growing trees. Different urban funtional areas bore the different tree bark pH, with a series of garden area >industrial area > heavily traffic area > domestic area (P< 0.05), which was owing to the pollution of SO₂ and other acid gases in different concentration in these areas. The SO₄^2- concentration of extractable bark solution of the same tree varied with the degree of SO₂ pollution, changing from 2.516 mg/g in relative clean site to 5.342 mg/g in polluted site. The relation between bark SO₄^2- and air SO₂ was Y = 2. 576 + 6. 4736X ( r =0 . 7 7 3 0 , P < 0 . 0 0 1 ) . Meanwhile, tree barks showed negative line relation between bark pH and SO₄^2- and air SO₂  was Y=7.1-0.3865X ( r=-0.8941, P<0.001). The results showed that the barks of four deciduous species such as Ulmus pumila L., Populus canadensis Moench, Salix babylonica L., Sophora japonica L. were sensitive to air SO₂ and could be used as the suitable indicator plant.