The morning smog was so thick that we could barely see buildings across the street.

smog 是 smoke（烟）和 fog（雾）两个词组合而成的复合词，指"烟雾和雾气的混合物"，即"雾霾"。这个词形象地描述了空气污染时常见的灰蒙蒙的天气现象。