Fog and smog

Fog consists of visible cloud water droplets or ice crystals suspended in the air at or near the Earth's surface. Fog can be considered a type of low-lying cloud and is heavily influenced by nearby bodies of water, topography(地勢), and wind conditions.

Smog is a type of air pollutant.

Photochemical smog is haze in the atmosphere accompanied by high levels of ozone and nitrogen oxides, caused by the action of sunlight on pollutants.

A dust storm is a meteorological (氣象) phenomenon common in arid (乾旱) and semi-arid regions. Dust storms arise when a gust front or other strong wind blows loose sand and dirt from a dry surface. Particles are transported by saltation and suspension, a process that moves soil from one place and deposits it in another.

Gust front is a storm-scale or mesoscale (intermediate scale) boundary separating thunderstorm-cooled air (outflow) from the surrounding air; similar in effect to a cold front, with passage marked by a wind shift and usually a drop in temperature and a related pressure jump.

Saltation is the movement of hard particles such as sand over an uneven surface in a turbulent flow of air or water.

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