Among the most important are sulphate aerosols: tiny particles produced by the combustion of coal and some sorts of oilthat float in the air, sully the lungs, kill millions—and also, by reflectingaway incoming sunlight, cool Earth.
这个冒号的意义是做讲解缘由？这个冒号后面是词还是句子，决定了后面这个加粗部分是多重定语从句修饰的词？还是一个定语从句修饰的句子？假如不是多重定语从句，produced第一个定语从句用过去分词的非谓语形式正好省略了which is，符合多重定语从句省略第一个定从的规则呀。
所以假如aerosols后面的冒号假如改成逗号，这句话是否就不成立了?
冒号后为一个名词词组，是前面名词sulphateaerosols的同位语。这个名词词组的中心词为 tiny particles，中心词被过去分词短语produced by the combustion of coal and some sorts of oil 修饰，然后tiny particles produced by the combustion of coal and some sortsof oil 作为先行词被that引导的定语从句修饰。因为过去分词短语不可以剖析为定语从句，所以这个句子中只有一个定语从句，并没多重（双重）定语从句，但你可以说名词tiny particles被双重定语修饰。假如你把过去分词短语改为定语从句，再把后面的that改为which，就得到双重定语从句了。比如：
Among the most important are sulphate aerosols:tiny particles that are produced by the combustion of coal and some sorts of oil which float in theair, sully the lungs, kill millions—and also, by reflecting away incomingsunlight, cool Earth.