Why is sulfur dioxide a corrosive agent in the air?

Because sulfur dioxide is one of the main pollutants in the atmosphere, it is an important symbol to measure whether the atmosphere is polluted. Serious sulfur dioxide hazards have occurred in many cities in the world, resulting in many people being poisoned or killed. In some towns of our country, the harm of sulfur dioxide in the atmosphere is more common and serious.

Sulfur dioxide can react with water and oxygen in the air to form acid rain.

Acid rain can lead to soil acidification. The soil in southern China was originally acidic, but later it was washed away by acid rain, which accelerated the acidification process. The soil in the north of China is alkaline, which has a strong buffering capacity against acid rain and cannot be acidified for a while. There is a lot of aluminum hydroxide in the soil. After soil acidification, it can accelerate the weathering of primary and secondary minerals containing aluminum in the soil, release a lot of aluminum ions and form aluminum compounds that can be absorbed by plants. Long-term excessive absorption of aluminum by plants will lead to poisoning and even death. Acid rain will also accelerate the loss of soil minerals and nutrients; Changing soil structure leads to poor soil and affects the normal development of plants; Acid rain can also induce plant diseases and insect pests, so that crops, especially wheat, will be greatly reduced. Under the influence of acid rain, the yield can be reduced by 13% to 34%. Soybeans and vegetables are also susceptible to acid rain, which leads to the decrease of protein content and yield. The impact of acid rain on forests is largely caused by the deterioration of soil physical and chemical properties. Under the action of acid rain, nutrients such as potassium, sodium, calcium and magnesium in the soil will be released and leached out with the rain. Therefore, long-term acid rain will leach out a lot of nutrients in the soil, resulting in a serious shortage of nutrients in the soil, thus making the soil barren. In addition, acid rain can release aluminum from stable state in soil, increase active aluminum and reduce organic complex aluminum. The increase of active aluminum in soil will seriously inhibit the growth of trees. Acid rain will inhibit the reproduction of some soil microorganisms and reduce the activity of enzymes, and nitrogen-fixing bacteria, bacteria and actinomycetes in the soil will be obviously inhibited by acid rain. Acid rain is very harmful to forest plants. According to the domestic simulation experiment on the influence of 105 woody plants, when the pH value of precipitation is less than 3.0, it can cause direct damage to plant leaves, making them turn green and yellow and begin to fall off. The longer the leaves are exposed to acid rain, the more serious the damage. Field investigation shows that in areas where the PH value of precipitation is less than 4.5, a large number of yellow leaves fall off in Pinus massoniana forest, Pinus armandii forest and Abies fir forest, and the trees decline and die in pieces. For example, in areas with precipitation PH less than 4.3 in fengjie county, the annual average height growth of 20-year-old Pinus massoniana stands is reduced by 50%. Acid rain will also significantly increase forest diseases and insect pests. In Sichuan, the disease index of Pinus massoniana forest in severe acid rain area is 2.5 times that in no acid rain area. The harm of acid rain to forests in China is mainly in the provinces south of the Yangtze River. According to preliminary investigation and statistics, the forest area harmed by acid rain in Sichuan Basin is the largest, about 280,000 hectares, accounting for 32% of the woodland area. The affected forest area in Guizhou is about 6.5438+0.4 million hectares. The research results show that only in the southwest of China, the forest productivity is reduced due to acid rain, and 6.3 million cubic meters of wood is lost, resulting in a direct economic loss of 3 billion yuan (calculated by market price 1988). According to the estimation of South China 1 1 province, the direct economic loss caused by acid rain can reach 4.4 billion yuan. Now most experts believe that the ecological value of forest far exceeds its economic value. Although there are still some disputes about the calculation method of forest ecological value, the calculated figures can not be generally recognized by the society, but the ecological value of forests exceeds its economic value, which is almost the same. According to these calculation results, the ecological value of forest is 2-8 times of its economic value. If calculated according to this ratio, the economic loss caused by acid rain to forest destruction is extremely huge.

4. Acid rain can dissolve hardened cement on the surface of nonmetallic building materials (concrete, mortar and lime-sand brick), produce cavities and cracks, reduce strength and damage buildings. Building materials become dirty and black, which affects the appearance and quality of urban landscape, and is called "black shell" effect. Acid rain is spreading in China, which is the third largest acid rain area in the world after Europe and North America. In 1980s, acid rain in China mainly occurred in Sichuan, Guangxi and Guangxi, represented by Chongqing, Guiyang and Liuzhou, with an area of 1.7 million square kilometers. By the mid-1990s, acid rain had spread to the south of the Yangtze River, the east of the Qinghai-Tibet Plateau and the vast areas of the Sichuan Basin, and the area of acid rain had expanded by more than 654.38+100,000 square kilometers. The acid rain areas in Central China, represented by Changsha, Ganzhou, Nanchang and Huaihua, have become the most polluted areas in the country. The annual frequency of acid rain in the central region is higher than 90%, and it is almost sour when it rains. The coastal areas of East China, represented by Nanjing, Shanghai, Hangzhou, Fuzhou, Qingdao and Xiamen, have also become the main acid rain areas in China. Acid precipitation also appeared in parts of North China and Northeast China. During the period of 1998, more than half of the cities in China experienced acid rain, including more than 70% of the southern cities and northern cities, such as Xi 'an, Tongchuan, Tumen and Qingdao. Acid rain has set off a prairie fire in China, covering more than 30% of the country. The harm of acid rain is various, including direct and potential harm to human health, ecosystem and building facilities. Acid rain will reduce children's immune function, increase the incidence of chronic pharyngitis and bronchial asthma, and increase the prevalence of eyes and respiratory tract in the elderly. For more than ten years, the problem of acid rain has become more and more prominent due to the increasing emissions of sulfur dioxide and nitrogen oxides. China is now the third largest acid rain area after Europe and North America. Acid rain in China is mainly distributed in Sichuan Basin, Guizhou, Hunan, Hubei, Jiangxi, Fujian, Guangdong and other coastal provinces. In North China, acid rain deposition is rarely observed, which may be due to less precipitation, low air humidity and low soil acidity in the north. However, it is worth noting that acidic precipitation has also appeared in northern areas such as Houma, Beijing and Tianjin, Dandong and Tumen.

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