冒号后为一个名词词组，是前面名词sulphate aerosols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 sorts of oil 作为先行词被that引导的定语从句修饰。由于过去分词短语不能分析为定语从句，所以这个句子中只有一个定语从句，并没有多重（双重）定语从句，但你可以说名词tiny particles被双重定语修饰。如果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。例如：

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 the air, sully the lungs, kill millions—and also, by reflecting away incoming sunlight, cool Earth.