Smoke is a very common phenomenon in life, but there have been a series of smoke "murders" that shocked the world in history. What's going on?
On December 5, 1952, a strong cold air flowed into the London area. The intersection of cold and warm air made the area appear thick fog and strong cooling from the evening. As the temperature dropped below 0 ℃, citizens burned coal for heating. On the morning of the 6th, people who got up early found that the outdoor visibility was very low and the lights must be turned on when driving on the road. What's more terrible is that many citizens feel dyspnea and tingling eyes. Many people can only lie down all night and can't even sleep until they feel suffocated. For a time, the number of patients going to the hospital surged unprecedentedly. In the next four days, the death toll in London reached 4000. It was not until December 9 that the thick fog gradually dissipated that everything gradually returned to normal.
However, in the next two months, thousands of people in London died of respiratory diseases due to smog. In 1956, 1957 and 1962, as many as 12 serious smog incidents occurred successively.
The main reason for this series of smog events in London is that factories and residents use a lot of coal, and the dust and sulfur dioxide in the exhaust gas accumulate over the city, causing dense fog weather. The dust produced by coal combustion will absorb a large amount of water on the surface and become the condensation core of smoke, which forms a dense fog. Ferric oxide in coal dust will also catalyze the oxidation of sulfur dioxide (SO2), another pollutant from coal, to form sulfur trioxide (SO3), which will then combine with the hydration adsorbed on the dust surface to form sulfuric acid droplets. These sulfuric acid droplets have a strong stimulating effect, and the weak will get sick or even die after inhalation.
As the "culprit" of the smog incident is soot, London smog is also known as "soot smog".
Another famous smog incident occurred in Los Angeles in the 1940s.
Located on the southwest coast of the United States, Los Angeles is a developed port city. However, since 1943, every year from summer to early autumn, as long as it is sunny, there will be a light blue smoke over the city, making the whole city foggy. Unlike the smog in London, where the weather is dark and humid, the smog in Los Angeles generally occurs at noon or afternoon on a sunny summer day with low humidity and temperature of 24 ~ 32 ℃.
Los Angeles smog is mainly caused by automobile exhaust and industrial exhaust emissions. After the olefin hydrocarbons and nitrogen dioxide (NO2) in automobile exhaust are discharged into the atmosphere, they will absorb the energy of sunlight under the strong sunlight and ultraviolet radiation, so as to produce ozone (O3), aldehydes, peroxyacetyl nitrate (Pan) and peroxybenzoyl nitrate (PBN) compounds. Because this chemical reaction is called photochemical reaction, the resulting smoke is also called "photochemical smoke".
Many substances produced in the process of photochemical reaction are harmful to human body, especially peroxyacetyl nitrate and peroxybenzoyl nitrate. Due to the reduced visibility during photochemical smog, it often leads to frequent traffic accidents.