再论都市霾与雾的区别

More Discussions on the differences between Haze and Fog in City

都市霾的出现有重要的空气质量指示意义,而雾或轻雾与特定的天气系统相联系。由于经济规模的迅速扩大和城市化进程的加快,都市霾现象或灰霾天气日趋严重,霾与雾的区分成为一个非常现实,又迫切需要解决的问题。东南沿海各省用相对湿度区分的标准普遍偏低,将大量霾记成了轻雾或雾。实际上近地层大气中每时每刻总是有霾存在的,而雾滴的存在是少见或罕见的;霾滴要想通过吸湿增长成为雾滴,必须有足够的过饱和度,能够越过过饱和驼峰才行,这在自然界并不容易。在非饱和条件下,不但非水溶性的霾不能转化成雾滴,即便是水溶性的霾粒子一般也不可能吸湿转化为雾滴。实测资料表明,出现雾时,极端最小相对湿度是91%,在相对湿度低于90%的情况下,没有观测到雾。降温是达到饱和形成雾滴的最主要、最重要的物理过程,在自然界中的霾滴通过吸湿过程增长成雾滴几乎不可能。历史上我国各级气象部门从来不存在以相对湿度70%界定轻雾与霾的补充规定。区分霾和雾,应该根据影响天气系统的变化,结合宏观特征的各种判据来确定。建议将相对湿度的阈值定为90%,作为区分轻雾与霾的辅助判据是合理的。

The appearance of haze has importance indication meaning to air quality, while the fog or light fog has specific weather indication relating to particular weather system. With the rapid development of economic scale and urbanization, the phenomena of haze or haze weather have become increasingly serious. The standard criterion by using relative humidity to distinguish haze or fog in many northeast coastal provinces is generally on the low side, leading to much haze weather recorded as light fog or fog. In the near surface atmosphere there always exists haze, while fog drop hardly exists. Only under the enough supersaturation which is higher than that the maximum of supersaturation can the haze nuclei become fog drop through moisture absorption growing, such a process is not easy to happen. Under non-saturation conditions, not only the insoluble haze nuclei are impossible to transform into fog drop, but also the soluble ones are commonly impossible. The observational data show that the extreme relative humidity is 91% when fog occurred, there is no fog when the relative humidity is lower than 90%. The most important physical process to form fog drop is by falling the temperature to the saturation point. It is hardly impossible to form fog drop through the natural moisture absorption growing of haze nuclei. The distinguishing of fog or haze should be made according to the change of weather system combining with the macrocharacteristics. It is rational by using the threshold value of relative humidity 90% as an assistant criterion to distinguish fog or haze.