Is it good for people to go out for a walk in foggy weather?

Fog is a fine water droplet (fog droplet) which is condensed by water molecules evaporated from the surface under the influence of cold air and suspended in the air. The radius of these tiny droplets is only 0.00 1 mm to 0.05 mm, and individual droplets are difficult to see clearly with naked eyes. Only when hundreds of millions of droplets get together can people form a clear fog. Fog with visibility less than 10 km is light fog, and fog with visibility less than 1000 m is heavy fog; The fog that can distinguish the sky overhead is distinguishable, but the fog that cannot distinguish the sky overhead is indistinguishable. From late autumn to early winter, the temperature decreases day by day, and its climatic conditions are more suitable for the formation of fog, so this is the season with frequent fog. Generally, the formation time of fog is from early morning to 8: 00 am, but the earliest appearance time of autumn fog can be from 2 1: 30 to 22: 00 in the first half of the night, and the fog is thickest in the morning, with different dissipation times. Some areas are affected by the terrain, with heavy fog and long fog days. Because the fog droplets are formed by the invisible water vapor cooling to saturation condensation, the size of the fog is related to the amount of water vapor in the air. The greater the air humidity, the more condensation nuclei (smoke particles, dust, etc.). ), the stronger the cooling effect, the more condensed water droplets, and the bigger and thicker the fog may be. Because the dust in the air is extremely rich, there are many buildings near the ground, and the wind speed is lower than that in the suburbs, it is easier to form fog in cities than in rural areas. However, the atmosphere of modern cities is polluted to varying degrees. The tiny water droplets in the fog dissolve and adsorb some pathogenic microorganisms and other harmful substances on the surface, of which the most important ones come from two aspects: one is harmful industrial dust and waste gas. Most foggy days belong to a cold and high-pressure weather system with low wind speed, often accompanied by strong inversion, which is not conducive to the diffusion of pollutants in the atmosphere. Tiny droplets make pathogenic substances harmful to human health, such as acid, alkali, phenol, amine, benzene, salt and heavy metal particles, stay and accumulate everywhere, which cannot be diffused and diluted. Various harmful substances often react with each other more frequently, producing more new toxic substances than before. Therefore, fog aggravates air pollution, accelerates the spread and diffusion of various pathogens, and intensifies the invasion of diseases on human body. It is an important factor to induce lung, trachea, bronchus, throat, nostrils, eyes, skin and other diseases, causing canceration, mutation or canceration. Second, hydrocarbons, nitric oxide and nitrogen dioxide emitted by automobiles react chemically under the action of sunlight, producing light blue photochemical smog composed of oxidants such as ozone, nitric oxide, formaldehyde, acetaldehyde, phenol and heavy metals, which will not only aggravate the smog, but also irritate people's eyes and mucous membranes, cause headaches, vomiting and respiratory disorders, easily induce chronic respiratory diseases, make children's lung function abnormal, and even cause death in severe cases. Because of this, among all kinds of pathogenic meteorological factors, fog poses the greatest threat to human health. The month with the most foggy days is also the season with tracheitis, laryngitis, pneumonia, rhinitis, conjunctivitis and allergic diseases, and the excess mortality rate of patients with pneumonia and lung cancer is as high as 40%. As for the hidden harm of some harmful substances inhaled to the body, it is immeasurable. In order to prevent the harm of fog to health, people living in cities should take active protective measures to minimize the harm of fog to health in foggy seasons. In particular, patients with respiratory and cardiovascular diseases, as well as people with allergies, physical weakness, the elderly and children, should pay more attention to reducing activities in foggy environment and avoid exercising or working for too long in foggy environment as much as possible.