‘Wù mái’ (smog) is a compound noun formed by combining ‘wù’ (fog) and ‘mái’ (haze). While ‘wù’ refers to water droplets suspended in air—natural and often harmless—‘mái’ denotes fine, dry particulate pollution (like dust, soot, or chemical aerosols) that reduces visibility and harms health. Together, ‘wù mái’ describes the hazardous, murky air mixture common in industrial or urban areas, especially during winter when temperature inversions trap pollutants near the ground.

This word carries strong environmental and public health connotations. It frequently appears in weather reports, government air-quality bulletins, and news about respiratory illness spikes. Unlike simple fog, ‘wù mái’ implies human-caused pollution and is often associated with PM2.5 particles, reduced sunlight, and restrictions on outdoor activities—especially for children and people with asthma or heart conditions.