What is the relative humidity? It's a foggy day.

Scientific knowledge: the difference between haze and fog

Generally speaking, when the relative humidity is less than 80%, the visibility deterioration caused by atmospheric haze blurred vision is caused by haze, while when the relative humidity is more than 90%, it is caused by fog. When the relative humidity is between 80% and 90%, the visibility deterioration caused by atmospheric haze blurred vision is caused by a mixture of haze and fog, but its main component is haze. The thickness of haze is relatively thick, which can reach about 1-3 km. Haze is different from fog and clouds, and there is no obvious boundary between haze and clear sky. Smog particles are evenly distributed and the particle size is relatively small, generally ranging from 0.00 1 micron to 10 micron, with an average diameter of about 1-2 micron. These particles in the air are invisible to the naked eye. Because the smog is composed of dust, sulfuric acid, nitric acid and other particles, the longer the scattering wavelength, the more the light ratio, so the smog looks yellow or orange-gray.