Daily Conversation: People use 雾霾 (wùmái) to talk about the daily air quality, make decisions about outdoor activities, and express concern for the health of children and the elderly.
News and Formal Reports: The media uses 雾霾 to report on air quality levels, visibility, and government initiatives to combat pollution. You'll often hear it in weather forecasts (天气预报).
Social Media: On platforms like Weibo, 雾霾 is a common topic for complaints, sharing photos of the low visibility (or a rare clear, blue sky), and sometimes as a metaphor for a gloomy or unclear situation (e.g., “my future feels like it's shrouded in wùmái”).
Connotation: The term is almost exclusively negative. It implies dirtiness, health risks, and a low quality of life. The opposite, a clear day, is celebrated as a “blue sky” (蓝天, lántiān).