"Death in the air" is the name people give to a kind of rain that stings people. This kind of stinging rain is "acid rain".

Under normal circumstances, the atmosphere contains a certain amount of carbon dioxide, which dissolves in water to form weakly acidic carbonic acid during precipitation, so normal rain is slightly acidic, with a PH value of about 5.6-5.7. 1In June, 982, the International Environment Conference officially defined precipitation with PH less than 5.6 as "rain, snow, frost, fog, hail, graupel, etc."

Acid rain ".

As early as 1872, human beings discovered acid rain, and relevant United Nations organizations also admitted in 1982 that it was a global environmental pollution problem.

After the Second World War, industries in various countries rose in succession, especially in Europe. Some countries and regions with high industrialization level can emit about 46 million tons of sulfide and nitrogen oxide smoke into the atmosphere through factory chimneys every year. Under the blowing of the wind, these smog react chemically during thousands of kilometers of long-distance transportation, generating sulfate. When sulfate meets water vapor, cloud drops, rain and snow, acid rain and mist fall to the ground, and then are collected in rivers and lakes by the current, which seriously threatens the survival of fish, other animals and plants and human beings. It is reported that in Sweden, thousands of tons of sulfur smog from abroad enter the country with the westerly wind across Europe every day. In the past 30 years, about 1/5 lakes in Sweden have been seriously acidified, and the PH value of the lakes has dropped below 5.0, so many fish eggs cannot hatch normally. In addition, the toxic metals in the mud at the bottom of the lake are dissolved in acid, which eventually leads to the death of fish. At present, the fish in more than 4,000 lakes in Sweden have disappeared; In Norway, there are 1838 lakes without live fish in more than 5000 lakes. More than 180 species of lake fish are extinct in the Adirondack Mountains in new york, USA. ...

The harm of acid rain to forests has also been frequently reported in newspapers in recent years. Leaves are particularly sensitive to acid rain. After the leaves are damaged, photosynthesis is reduced, and the ability to resist pests and diseases is weakened, resulting in slow growth and even death of trees. In western Germany, it is estimated that in the past 10 years, 12% of forests have been destroyed. The annual wood loss caused by acid rain in Sweden is 4.6 million cubic meters.

Acid rain can also corrode open-air buildings and pipeline facilities. For example, the statue of Charles I in Trafalgar Square in London, the Colosseum in Rome and the Parthenon in Athens were all damaged to varying degrees. China also has many examples. For example, the Jialing River Bridge corrodes at the rate of 0. 1.6 mm every year, and the maintenance cost of steel structure alone exceeds 200,000 yuan every year.

More seriously, acid rain can also dissolve copper and lead in drinking water, which directly harms human health. Drinking groundwater with high content of acidified heavy metals and eating fish in acidified lakes and rivers can make some heavy metal elements accumulate in human body through the food chain, which will eventually cause harm.

In addition, inhaling air containing acidic substances will aggravate human respiratory diseases. Acid rain contains formaldehyde, acrylic acid and other components, which has a strong stimulating effect on human body and eyes. The toxicity of sulfuric acid mist and sulfuric acid mist is 10 times higher than that of carbon dioxide, and its particles can invade deep tissues of human body, causing pulmonary edema, pulmonary sclerosis and other diseases and leading to death. At present, the main distribution areas of acid rain in China are Sichuan Basin, Guizhou, Hunan, Hubei, Jiangxi, Fujian, Guangdong and other coastal provinces, accounting for 30% of China's land area.

The background of the news story

In 2004, the acid rain pollution in China was aggravated.

According to the State Environmental Protection Administration's "Bulletin on China's Environmental Situation in 2004", the acid rain pollution in China showed a slight increasing trend in 2004. Statistics show that acid rain occurred in 298 cities in China in 2004, accounting for 56.5% of the 527 statistical cities (counties) in China. There are 2 18 cities with annual precipitation pH less than 5.6 (acid rain), accounting for 4 1.4% of the statistical cities. Compared with the previous year, the proportion of acid rain cities increased by 2. 1 percentage point; The proportion of cities with acid rain increased by 4 percentage points, and the proportion of cities with pH less than 4.5 increased by 2 percentage points. The proportion of cities with acid rain frequency exceeding 80% increased by 1.6 percentage points.

The report shows that the regional distribution of acid rain was basically stable in 2004, and the cities with annual precipitation pH less than 5.6 (acid rain) were mainly distributed in Central China, Southwest China, East China and South China. The acid rain area in Central China is the most polluted, and Hunan and Jiangxi are the most polluted areas.

The main distribution areas of acid rain in China are Sichuan Basin, Guizhou, Hunan, Hubei, Jiangxi, Fujian, Guangdong and other coastal provinces, accounting for 30% of China's land area.