In the last 30 years of the 20th century, the United States, the United Kingdom, and Japan have experienced deadly smog incidents that caused significant losses.
Before the 1960s, there were already 8 major pollution incidents worldwide, with smog accounting for 5 of them, resulting in numerous accidents and wide-ranging impacts. The most notable incidents include the Great Smog of London (UK) and the Los Angeles Smog (USA). These events represent two different types of smog. The Great Smog of London was an oxidizing-reducing smog primarily caused by sulfur oxides, while the Los Angeles Smog was a photochemical smog mainly caused by ozone and other pollutants.
Under certain geographical and weather conditions, air pollutants can accumulate in specific areas. The incident of smog
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| The Great Smog of London – December 5-8, 1952, caused 4,000 deaths in just 4 days (Photo: pyr.ec.gc.ca) |
in London formed under such conditions. London is a major city with a history of over 2,000 years, located in the expansive Thames River estuary. From December 5-8, 1952, there was no wind in London. It was winter, with very low temperatures, high humidity, and heavy atmospheric pressure, resulting in a thick fog that obscured sunlight for several days. Thousands of chimneys continued to emit smoke into the sky, creating dense black columns of smoke, with dust concentrations 10 times above normal and SO2 levels 6 times higher. The Fe2O3 in the smoke reacted with CO2 in the air to form H2SO4 droplets, which condensed in the smog, creating acid clusters. This resulted in over 4,000 deaths within 4 days. Two months later, nearly 8,000 more people died consecutively. At that time, the causes were not well understood, leading to a lack of effective treatment and prevention measures. In 1957 and 1962, London experienced further deadly smog incidents. The UK government compared the smog events of 1952 and 1962 to identify the causes of harm.
Photochemical smog forms under specific climatic conditions through complex photochemical reactions of air pollutants. It occurs when there is sufficient sunlight, a high concentration of nitrogen oxides and hydrocarbons, and unfavorable geographical and climatic conditions that hinder the dispersion of these pollutants. The deadly smog incident in Los Angeles met all three of these conditions, resulting in photochemical smog.
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| Los Angeles in the 1940s had over 2.5 million vehicles, with automobile emissions causing photochemical reactions (Photo: bardaglea) |
Los Angeles is an industrial city located in a 50 km long basin facing the ocean, surrounded by mountains. In the early 1940s, a type of light blue smog began to appear in Los Angeles, lingering for days and causing residents to experience symptoms such as sore throats, eye irritation, sneezing, headaches, and nausea. After extensive investigation, it was discovered in 1951 that this smog was caused by automobile emissions. At that time, Los Angeles had over 2.5 million vehicles, consuming 16,000 liters of gasoline daily. These cars emitted nitrogen oxides, hydrocarbons, and CO. Due to the intense sunlight during the summer and early fall in Los Angeles, photochemical reactions occurred with the compounds in automobile emissions, resulting in photochemical smog primarily composed of O3. This type of smog caused the aforementioned symptoms, and in severe cases, it could lead to breathing difficulties, reduced vision, and paralysis of limbs. Prolonged exposure could also result in arterial hardening and decreased physiological function.
Currently, cities with high concentrations of vehicles continue to face the threat of photochemical smog, with a lack of effective prevention measures.
