2. In addition, sunshine hours and solar radiation in urban areas decrease due to the increase of urban cloud cover. Due to the increase of smoke particles in cities and the deterioration of atmospheric transparency, some people call cities "haze islands" or "turbid islands". Smoke and dust greatly weaken the ultraviolet part of sunlight (even 30%-50% when the sun is low), which is also unfavorable to the health of urban residents.
3. Acid rain will 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 to acid rain, and it will not be acidified for a while. The soil contains a large amount of aluminum hydroxide, which can accelerate the weathering of primary and secondary minerals containing aluminum in the soil, release a large amount 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 nutrients in soil minerals. 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, potassium, sodium, calcium, potassium and other nutrients in the soil. 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 a stable state, increase active aluminum and reduce organic complex aluminum. The increase of active aluminum in soil will seriously inhibit the growth of trees. Acid rain can inhibit the reproduction of some soil microorganisms and reduce the activity of enzymes. Acid rain has obvious inhibitory effect on nitrogen-fixing bacteria, bacteria and actinomycetes in soil. 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 directly hurt the leaves of plants, make them turn green and yellow and start to fall off. The longer the leaves are exposed to acid rain, the more serious the damage. Field investigation shows that in the area 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 forests decline in pieces. For example, in fengjie county, Chongqing, where the precipitation PH value is less than 4.3, 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 affected by acid rain in Sichuan Basin is the largest, about 280,000 hectares, accounting for 32% of the forest area. The affected forest area in Guizhou is about 6.5438+0.4 million hectares. According to the research results, only in southwest China, the forest productivity decreased due to acid rain, * * * lost 6.3 million cubic meters of wood, and the direct economic loss was 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 losses caused by acid rain to forests are extremely huge.
4. Acid rain can dissolve hardened cement on the surface of nonmetallic building materials (concrete, mortar, 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, covering an area of 6.5438+0.7 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. The area of acid rain has expanded by more than 1 10,000 square kilometers. The acid rain areas in central China, represented by Changsha, Ganzhou, Nanchang and Huaihua, have become the most polluted areas in China, and the annual frequency of acid rain in central China is higher than 90%. Almost to the point where it will be 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 rain has also appeared in some areas of North China and Northeast China. From 65438 to 0998, more than half the cities in China, including more than 70% southern cities and Xi 'an, Tongchuan, Tumen and Qingdao, suffered from acid rain. Acid rain has appeared in China. Coverage has accounted for more than 30% of the land area. Acid rain has many hazards, including direct and potential hazards to human health, ecosystems and building facilities. Acid rain will reduce children's immune function, increase the incidence of chronic pharyngitis and bronchial asthma, and increase the incidence of eyes and respiratory tract in the elderly. For more than ten years, the problem of acid rain has become more and more serious 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. The main distribution areas of acid rain in China are Sichuan Basin, Guizhou, Hunan, Hubei, Jiangxi, Fujian, Guangdong and other coastal provinces south of the Yangtze River. 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. But it is worth noting that in the north, such as Houma, Beijing, Tianjin, Dandong and other places.