Among all the air pollution problems in China, acid rain is the biggest one. Acid rain is rainfall that has been acidified. It usually has a pH lower than 5.6. It is formed when pollutants called oxides of sulfur and nitrogen, contained in power plant smoke, factory smoke, and car exhaust, react with the moisture in the atmosphere. Dry deposition, such as soot and ash, sleet, hail, snow, smog and low level ozone are forms that acid rain can take. As the emission of sulfur dioxide and nitrogen oxide keeps increasing, the problem has becomes more and more serious. Now China is the third largest acid rain area, only next to Europe and North America.
There are many problems and effects caused by acid rain. It can cause buildings, statues and bridges to deteriorate faster than usual, and will pollute thousands of lakes, rivers, and streams worldwide. It will damage the ecosystems of the lakes and kills wildlife in these affected lakes, rivers and streams. It can also damage soil and the tree roots in it. When soil is acidified, tree roots are damaged, leaving them not able to draw in enough nutrients to support the tree. It will bring great harms to forest plants. Under this effect, nutrients in soil will be released, and leached out with the rain. As a result, the soil will become barren. In addition, it can make the aluminum elements in the soil released out from the stable state, so that the activated aluminum in the soil will be increased, which could seriously inhibit the growth of trees. When acid rain falls on trees, it will make their leaves turn brownish-yellow and the tree can no longer carry out photosynthesis properly.
The main areas affected by acid rain in China are the areas in the south of the Yangtze River, such as Sichuan Basin, Guizhou, Hunan, Hubei, Jiangxi, and some coastal provinces such as Fujian and Guangdong. According to preliminary survey, the forests in Sichuan Basin is the largest area damaged, which is about 28 million hectares, accounting for 32% of the woodland area.
China has made great efforts on researches about acid rain for nearly 30 years. However, it is still quite limited in the funding, size and depth of the research. As a result, China still has a lot to do to solve the problems brought it.