Oxides of sulphur and nitrogen are emitted in gaseous form wherever coal and petroleum are widely used--such as in the combustion of petrochemical raw materials, high-temperature engines in industrial plants, power plant generators, and vehicular traffic.
而硫與氮的氧化物，則是人類大量利用煤與石油﹘﹘石化原料的燃燒、工業區內工廠高溫引擎運轉、發電廠機器轉動、交通工具發動行進…… 釋放出的氣體。