“Fog” is a clunky name for a cloud, especially one that appears so delicate and ethereal. It’s a simplistic name, too, one that doesn’t do justice to the myriad and nuanced forms fog assumes across the globe. Meteorologists have added some polysyllabic complexity by describing several basic fog types: radiation fog, advection fog, freezing fog, ice fog, and upslope fog. Few people (including weather reporters) use these names. We rely instead on generic adjectives—“thick,” “dense,” “heavy,” “patchy,” or “light”—to describe most fogs we encounter.
Can’t we do better? Why, the Eskimos have fifty words for snow!
In fact, we have done better. A recent moderate-effort search in my guidebooks to the weather, textbooks on atmospheric science, and cloud-related websites, yielded these names: air hoar, acid fog, advection fog, antarctic sea smoke, arctic sea smoke, arctic mist, black fog, cacimbo, California fog, caribou fog, dry fog, evaporation fog, flash fog, fog streamer, fog bank, fog bow, fog belt, fog drip, fog horizon, force 10 fog, frontal fog, frost smoke, frozen fog, freezing fog, frost smoke, ground fog, high fog, hill fog, ice fog, killer fog, London Fog, mixing fog, mist, monsoon fog, pea souper, pogonip, precipitation fog, radiation fog, frost flakes, rime fog, sea fog, sea mist, sea smoke, smog, steam devil, steam fog, supercooled fog, tule fog, upslope fog, and valley fog, and water smoke.
Unless you live in the U.K., you might not know about the "pea souper," the local name for the famous and infamous thick fog that occurs there. Thick fogs have always occurred naturally in London, but they became increasingly toxic during the Industrial Revolution when factories and fireplaces belched black smoke and soot from burning cheap sulfur-laden coal. Once-benign fogs formed around the particles of smoke and soot and became dangerous to breathe.
In December 1952, one especially thick pea souper hung over London for five days and caused widespread coughing, choking, bronchitis, lung inflammation, and the deaths of 12,000 people from respiratory failure. An estimated 4000 people died during the five days and another 8000 in the months afterward.
This nightmarish cloud event and public-health crisis lead to the passage of the 1956 Clean Air Act in the United Kingdom. Though coal burning has decreased, pea soupers still occur in London, though they contain the “smoke” of automobile exhaust and industrial air pollutants instead of burning coal. In London as elsewhere, this menacing cloud is known as smog—a name derived from combining smoke and fog.