That's normal, "explains Lin." But when the pH of rainfall drops to less than 5.0, that's definitely an unnatural, manmade phenomenon. And that's the definition of acid rain. "
「自然界的雨水原本就略帶酸性，這是正常現象，但若是 pH 值低於 5.0 以下，那顯然就是『非自然』的人為因素造成，這就是我們所定義的『酸雨』。」