Observation conducted abroad of dust on walls or in crannies of buildings has found that if any such dust containing sulphurous or nitrous oxides comes into contact with moisture, the action of photosynthesis turns it into sulphuric or nitric acid. Its effect on buildings can be seen in corrosion, rusting, crumbling and deterioration of various kinds.
根據國外觀察建築物牆上或孔隙間藏匿的粉塵，發現其中就帶有硫與氮的氧化物，若碰到濕氣，再加光合作用… …，就變硫酸與硝酸了，它對建築物的傷害則「斑斑可考」﹘﹘腐蝕、生鏽、脆裂…… 花樣多多。