What do the four horizontal symbols in the weather forecast mean?

Haze, fog, haze. There is a great difference between fog and haze. Haze means haze. The aerosol system composed of dust, sulfuric acid, nitric acid and other non-aqueous substances in the air causes visual impairment. The difference between haze and fog is that the relative humidity is small when haze occurs, but it is saturated in fog (if there are a large number of condensation nuclei, the relative humidity may not reach 100%, and saturation may occur).

First, sulfur dioxide, nitrogen oxides and inhalable particles are the main components of smog. The first two are gaseous pollutants, and the last particulate matter is the chief culprit that aggravates smog weather pollution. Together with the fog, they make the sky gloomy in an instant. The abbreviation of particulate matter is PM, and what Beijing monitors is fine particulate matter (PM2.5), that is, pollutant particles with a diameter less than or equal to 2.5 microns. This particle itself is not only a pollutant, but also a carrier of toxic substances such as heavy metals and polycyclic aromatic hydrocarbons.

Second, the sources of toxic particulate matter in cities: First, automobile exhaust. Cars that use diesel are "habitual criminals" who emit particles. Small cars that use gasoline emit gaseous pollutants, such as nitrogen oxides, which are easily converted into secondary particulate pollutants in foggy days, aggravating smog.

Fog is an aerosol system composed of a large number of tiny water droplets or ice crystals suspended in the air near the ground, which often appears in autumn and winter (which is also one of the reasons for the large-scale haze weather in China in June 20 13), and is the product of water vapor condensation (or condensation) in the air near the ground. The existence of fog will reduce air transparency and worsen visibility. If the horizontal visibility of the target drops below 1000m, the weather phenomenon of water vapor condensation (or condensation) suspended in the air near the ground is called fog. The phenomenon that the horizontal visibility of the target is 1000- 10000 meters is called light fog or mist. When fog is formed, the atmospheric humidity should be saturated (if there are a large number of condensation nuclei, the relative humidity may not reach 100%, and saturation may occur). Because the light scattered by fog composed of liquid water or ice crystals has little to do with wavelength, the fog looks milky white or bluish white and gray.

Haze is composed of particles such as dust, sulfuric acid, nitric acid and organic hydrocarbons in the air. It will also make the atmosphere turbid, blur the vision and worsen the visibility. If the horizontal visibility is less than 65,438+00,000 meters, the sight distance obstacle caused by this non-aqueous aerosol system is called haze or dust haze, and the Hong Kong Observatory calls it haze.

Hazards of smog

Upper respiratory tract infection (URTI)

The persistent smog weather has enveloped more than 65,438+00 provinces in China. Hazy weather, a large number of harmful substances such as dust particles and smoke particles floating in the air will cause harm to the human respiratory tract. There are a lot of particles, dust, pollutants and viruses floating in the air. Once inhaled by the human body, it will stimulate and destroy the respiratory mucosa, dry the nasal cavity, destroy the defense ability of the respiratory mucosa, and bacteria will enter the respiratory tract, which is easy to cause upper respiratory tract infection.

bronchial asthma

The air pollution in foggy days is heavier than usual, and bacteria and viruses often exist in the air, which is easy to lead to the spread of infectious diseases and the occurrence of various diseases. In particular, air pollutants in cities are not easy to spread, which aggravates the toxicity of sulfur dioxide, carbon monoxide, nitrogen oxides and other substances and will seriously threaten people's lives and health. In foggy days, dust and smoke are floating in the air, and dust mites may also be suspended in the fog. Inhalation of these allergens by patients with bronchial asthma will stimulate the respiratory tract and cause asthma symptoms such as cough, sulking and poor breathing.

lung cancer

Professor Kan Haidong from the School of Public Health of Fudan University said that the incubation period of lung cancer ranges from several years to decades, and children's childhood lung cancer may be related to genetic factors and gene mutations. However, compared with adults, children's height determines that they are indeed more susceptible to automobile exhaust and road dust, which is recognized by the medical community. Because children's breathing zone is just close to the height of waste gas, at the same time, children's exposure per unit weight is higher than that of adults, which leads to their higher susceptibility, so they are more susceptible to pollution gases such as waste gas and smog. In addition, children's body organs are not fully developed, and the invasion of polluted gas causes more harm.

conjunctivitis

According to experts, particulate matter attached to the cornea in foggy days may cause keratitis and conjunctivitis, or aggravate the condition of patients with keratitis and conjunctivitis. Patients with keratitis and conjunctivitis have increased significantly, including the elderly and children, as well as office workers who face computers all day. Everyone has the same situation: dry eyes, soreness, tingling, redness and allergies.

Infantile rickets

The Environmental Research Institute of China Center for Disease Control and Prevention spent a year studying the effects of smog on human health.

The preliminary study found that the smog weather not only led to an increase in the incidence/hospitalization rate of respiratory diseases, but also had some indirect effects on human health. Haze will weaken ultraviolet radiation. If smog often occurs, it will affect the synthesis of vitamin D in human body, lead to a high incidence of rickets in children and enhance the activity of infectious bacteria in the air.