What do you mean by foggy days?
A particulate matter is the chief culprit that aggravates smog weather pollution. They combine with fog and instantly turn the sky gray. The abbreviation of particulate matter is PM, and what Beijing monitors is PM 10, that is, pollutant particulate matter with a diameter less than 10 micron. This particle itself is not only a pollutant, but also a carrier of toxic substances such as heavy metals and polycyclic aromatic hydrocarbons. With the deterioration of air quality, cloudy days are increasing and the harm is increasing. In many areas of our country, the smog weather phenomenon is combined with fog as an early warning and forecast of disastrous weather. Collectively referred to as "haze weather". In fact, fog and haze are completely different to some extent. For example, when fog appears, the air is humid; When smog occurs, the air is relatively dry and the relative humidity of the air is usually below 60%. The reason is that a large number of extremely fine dust particles, smoke particles and salt particles float in the air evenly, so that the air with effective horizontal visibility less than 10KM is mixed together. The symbol is "∞". The diurnal variation of haze is generally not obvious. When the air mass changes little and is stable, it lasts for a long time, sometimes exceeding 10 days. Due to weather phenomena such as haze, light fog, sandstorm, sand blowing, floating dust and smoke, the effective horizontal visibility is less than 10KM due to a large number of extremely fine dust particles or smoke particles floating in the air. Sometimes it is difficult for meteorological professionals to tell the difference. It is necessary to comprehensively analyze and judge the weather background, sky conditions, air humidity, color and smell, satellite monitoring and other factors to draw a correct conclusion. The weather phenomena of fog and haze can sometimes be converted to each other.
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