Ask about the knowledge of acid rain

First, the definition of acid rain

"Acid rain", as the name implies, rain is sour. Its correct name should be "acid sedimentation", which can be divided into "wet sedimentation" and "dry sedimentation". The former refers to all gaseous pollutants or granular pollutants that fall to the ground in the form of precipitation such as rain, snow, fog or hail, while the latter refers to acidic substances carried by dust falling from the air in rainy days. Chemically, it is defined that the pH value of water is equal to 7, which is neutral and less than acidic. The natural atmosphere contains a lot of carbon dioxide. Carbon dioxide is dissolved in rainwater at room temperature, and after reaching gas-liquid equilibrium, the pH value of rainwater is about 5.6, so natural rainwater is acidic. However, in nature, there are other acid-causing substances, such as hydrogen sulfide emitted by volcanic eruption, dimethyl sulfide released by the ocean, nitrogen oxides produced by high-altitude lightning and so on. This will further acidify the rainwater and reduce the pH value to about 5.0. Therefore, since the late 1980s, many researchers at home and abroad (including the research report of the Environmental Protection Agency) have acknowledged that the so-called "acid rain" is the influence of man-made acidic pollutants when the pH value of rainwater is lower than 5.0. Therefore, in the research report of the Environmental Protection Agency, it has been uniformly stipulated that when the pH value of rainwater reaches below 5.0, it is officially defined as "acid rain". For example, according to the effective rainwater chemical analysis data of Taipei Acid Rain Monitoring Station 1990- 1998 of the Environmental Protection Agency, about 90% of rainy days have a pH below 5.6, and the probability of acid rain is about 75%.

Second, the composition of acid rain

In the general chemical composition of acid and water, the more important species include H+, Cl-, NO3-, so42-, NH4+, K+, Na+, Ca2+ and Mg2+. Its sources include

The figure shows natural sources and artificial sources. Generally speaking, NO3- and so24- are the main acid-causing substances, and their sulfur oxides and nitrogen oxides are transformed. In terms of man-made pollution discharge, the former is related to the use of fossil fuels, thermal power plants and the combustion of sulfur-containing organic matter; The latter mainly comes from factors such as high temperature combustion process in factories and automobile exhaust emissions. Ca2+ and NH4+ are the main neutralizing substances.

Artificial acid-causing substance

Artificial alkaline substance

SO2-4 petrochemical industry, thermal power plant, seawater droplet combustion Na+, Cl- and Mg2+.

NO3- Ca2+ and K+ dust emitted by factories and vehicles during high-temperature combustion.

NH4+ pesticide spraying

To clarify a concept here, whether the pH value of rainwater is high or low does not necessarily mean that there are other basic ions such as ammonium, calcium and magnesium to neutralize its acidity, and the pH value of rainwater is calculated by hydrogen ions after the above ions are balanced. In other words, if there are high concentrations of sulfate ions and nitrate ions in the rain, but there are other alkaline ions to neutralize them, then the rain may not show an acidic reaction (that is, the pH value is low), and vice versa. There is no doubt that the pH value of rainwater can be used as an early indicator, but it is more important to further analyze the chemical composition of rainwater, understand the source of pollutants, calculate the pollutant flux (so-called settlement, unit is kg/ha/ year) that sinks to the surface with rainwater, and then formulate control strategies to improve it.

Third, the harm of acid rain.

mankind

The most direct reaction to the impact of acid rain on human beings is baldness, but scientists are still trying to study whether it will really lead to baldness, but it is better for everyone to rain less.

The most serious side effect of acid pollution on human beings is respiratory problems. Emissions of sulfur dioxide and nitrogen dioxide can cause respiratory problems, such as asthma, dry cough, headache and eye, nose and throat allergies. For human beings, an indirect effect of acid rain is that toxic metals dissolved in water are absorbed by fruits, vegetables and animal tissues. Although these toxic metals will not directly affect these animals, eating these animals will have a serious impact on human beings. For example, mercury accumulated in animal organs and tissues is related to brain injury and neurological disorders. Similarly, another metal aluminum in animal organs is related to kidney problems, and it has recently been suspected to be related to Alzheimer's disease.

Buildings and statues

Acid particles can also be deposited on buildings and statues, causing erosion. For example, the US Capitol in Ottawa has been decomposed by excessive sulfur dioxide in the atmosphere. Limestone and marble become a broken substance called gypsum when they come into contact with acid. In addition, bridges are corroded faster, and the railway industry and aircraft industry must spend more money to repair the damage caused by acid rain. Acid rain not only causes economic burden, but also poses a threat to public safety. For example, 1967, the Ohio River Bridge collapsed and 46 people were killed. What is the reason? Due to the corrosion of acid rain.

In addition, acid rain has also led to the erosion of exposed statues, resulting in the destruction of cultural assets, which has worried many people.

crops

Acid rain will affect the leaves of rice, at the same time, the metal elements in the soil will be dissolved by acid rain, resulting in a large loss of minerals, plants will not get enough nutrition, and will wither and die. However, the metals released by acid rain in soil may also affect the absorption of plants. This problem is extremely complicated. For example, the release of some metals (such as iron) in acid rain will help the growth of plants. Therefore, the exact impact of acid rain on plants, crops and forests is still unclear.

The picture on the left shows the leaves being damaged by acid rain.

The picture on the right shows the internal tissue of the blade observed under the microscope.

Trees and soil

One of the most serious effects of acid rain is in forests and soil. Sulfuric acid falls to the ground with rainfall, causing serious damage, and nutrients in the soil will also be lost, so trees will die because of the loss of calcium and magnesium necessary for life. Not all sulfur dioxide will be converted into sulfuric acid. In fact, a considerable part will float in the atmosphere and eventually sink to the surface, which will hinder the photosynthesis of leaf stomata. The results showed that the seedlings of Picea koraiensis were sprayed with a mixture of sulfuric acid and nitric acid with a pH of 2.5 to 4.5, and brown damage was observed. Finally, the number of needles will decrease, and it is found that the growth rate of needles in areas with high acidity concentration is slow, because the death rate of needles in this area is faster than the regeneration rate, and photosynthesis is also greatly affected.

In addition, severe frost may make this situation worse. With the increase of sulfur dioxide, ammonia and ozone in the air, the frost resistance of trees will decrease. Ammonia oxide and sulfur dioxide produced by ammonium sulfide will form on the surface of trees. When ammonium sulfate reaches these soils, it will react to produce acidic substances containing sulfur and nitrogen, which will stimulate the growth of harmful animals such as fungi and beetles.

Forestry is an industry with an annual value of10 million yuan in Canada, and about 10% of Canadians depend on cutting and processing trees for a living. If the forest is in danger, these occupations will disappear with it.

Fourth, the status quo of Taiwan Province Province.

The earliest research on acid rain in Taiwan Province Province was the rain survey conducted by central weather bureau at Taibei Weather Station, and the lowest pH value was 3.8 at that time. From April, 65438 to April, 0990, the Environmental Protection Department began a long-term acid rain research on the whole island. The survey results show that acid rain has become very common in Taiwan Province Province. If pH=5.0 is taken as the benchmark to judge acid rain, the probability of acid rain in Taiwan Province, Taibei and Kaohsiung is 52%, 85% and 74% respectively, which is significantly higher than the statistical results of the whole Taiwan Province province (Zheng, 1998), and the probability of acid rain in Alishan is 28%, far less than that in the capital circle. This is related to the large number of cars and factories in metropolitan areas, which leads to serious acidification of rainwater.

Distribution map of pH value of rainwater in Taiwan Province Province

At present, the distribution of acid rain in Taiwan Province Province is bounded by Jian 'an Plain, and gradually acidifies to the south or north. Therefore, Jianan Plain can be said to be the main area where rainwater is not acidified in Taiwan Province Province, and another area which is not acidified is Kenting at the southern tip of Taiwan Province Province, but it only accounts for a small part.

According to the monitoring results of Environmental Protection Bureau (199 1- 1997), the pH value of rainwater in Taipei is the lowest in all regions, only about 4.3. Followed by Guishan and Zhongli stations near Taipei, with pH values below 4.5. Kaohsiung and Taichung stations are also areas with serious acid rain, with an average pH of around 4.6. Taimali, Yilan, Kenting and Alishan are areas with low degree of rainwater acidification.