When the weather is clear, the clean atmosphere makes the sky look blue, which is particularly pleasing to the eye. On the contrary, once the atmosphere is polluted, even if it is sunny, the sky will become gray and foggy. In this way, people will feel depressed, unwell and in a worse mood. A clean atmosphere usually contains 78% nitrogen, 265,438+0% oxygen, 0.03% carbon dioxide, 0.93% argon and trace amounts of other gases, such as ozone, methane, ammonia, neon and helium. Once the atmosphere is polluted, it means that the proportion of various gases is out of balance. Scientists have found that at least 100 kinds of air pollutants are harmful to the environment, among which sulfur dioxide, nitrogen oxides, carbon monoxide and chlorofluorocarbons are more threatening to human beings.
Some natural phenomena will affect the composition of the air and cause air pollution. For example, volcanic eruption spews a lot of carbon dioxide and dust into the air; Lightning and thunder sometimes cause forest fires, consuming oxygen and increasing carbon dioxide in the air. However, these effects are not common and lasting, and the air can recover itself after a period of time.
The unreasonable production and living activities of human beings have caused extremely serious pollution to the atmosphere. Many large modern factories constantly discharge various substances into the atmosphere, including many toxic and harmful substances. According to statistics, the world emits more than10.50 billion tons of sulfur dioxide, more than 200 million tons of carbon dioxide, 2.3 billion tons of suspended particles and 69 million tons of nitrogen oxides every year. This will cause extremely serious pollution to the atmosphere, make the air composition unable to recover for a long time, and even have a negative impact on people and other creatures. People and creatures can't feel the mild air pollution at that time, and after a long time, various diseases will occur; Serious pollution is easy to cause tears, cough, headache and nausea; Especially serious, it will make people suffocate and even die.
Air pollution not only affects human health, but also changes meteorological laws. Global warming, acid rain and ozone hole are all caused by air pollution in the final analysis.
According to the effects of various substances entering the atmosphere on human health, biology and climate, scientists have formulated the maximum allowable concentration as a standard. If a substance exceeds the standard, it means that the atmosphere is polluted. The more it exceeds the standard, the more serious the pollution is. Nowadays, many big cities in China, such as Beijing and Shanghai, release air quality reports to citizens every day.
When it comes to air pollution, people often naturally think of harmful gases such as hydrogen fluoride, hydrogen chloride, sulfur dioxide and carbon monoxide in the air. In fact, in addition, fine particles floating in the air are also serious pollution sources. These particles with a diameter less than one millionth of a meter are named "PM 10" and people call them "air killers". Some experts believe that it is the chief culprit that causes many deaths in London every year. An article in The New York Times, USA, said: The latest calculation by an environmental protection organization shows that more than 5,000 people die each year in Los Angeles and more than 4,000 in new york.
The British magazine "New Scientist" reported that scientists from the United States, Poland and the Czech Republic conducted research in heavily polluted Eastern Europe, and concluded that particulate pollution would hinder the growth and development of the fetus in the uterus. Frederica Pereira of Columbia University in new york said at a medical conference in Budapest that if a woman lives in an environment with high particulate pollutants during pregnancy and gives birth to a baby with a small head and trunk, the risk of cancer of these children may increase, and their future learning ability may be affected. The magazine New Scientist also reported that a study conducted by the US Environmental Protection Agency in the Czech Republic and North Bohemia, China, had the same result.
A study of 239 cities by the Natural resources defense council shows that if the weight of particles in the air per cubic meter is limited to no more than 20 mg, 4,700 lives may be saved every year. If it is limited to 10mg, about 56,000 lives can be saved every year. Some people have determined that when the suspended particulate matter in the air reaches 100 microgram, children's asthma increases obviously; When it reaches 200 micrograms, the mortality rate of the elderly and infirm increases.
What is even more worrying is that the change of heart disease incidence is closely related to the increase or decrease of air particles. When the number of air particles increases, the number of people who die of heart disease will also increase sharply. Dr Douglas Dockery of Harvard School of Public Health found evidence of a link between death and airborne particles when he investigated six cities in the United States.
Although the mechanism of heart disease caused by air particles remains to be studied, considering that blood must pass through the lungs, Dr. Dockery thinks there may be two reasons: 1. Physical reasons. In recent years, scientists have found that people inhale a lot of particles into the depths of the lungs every time they breathe. Under normal circumstances, about 500 thousand particles are inhaled at a time. When these particles enter the depths of the lungs, they will remain in the lungs as routine irritants. This irritant can cause inflammation and produce mucus, making breathing difficult and even leading to death. 2. Chemical reasons. Particulate matter can be used as a medium to bring chemical pollutants (such as acid, lead, mercury and other metals) into the depths of the lungs, which will accelerate the production of harmful substances such as free radicals.
There are many sources of particulate matter in the air, among which coal-fired power plants produce the most particulate matter, and the particulate matter emitted by burning 1 ton of coal reaches 10 kg. Various types of motor vehicles and industrial boilers that use gasoline and diesel as energy sources also produce a large number of particles. In addition, there are dust on the bare ground blown by strong winds, particulate matter emitted by metallurgical enterprises, lime plants and cement plants in industrial areas, nitrate particulate matter generated by nitrogen oxides emitted by vehicles, sulfate particulate matter generated by sulfur oxides emitted by power plants, etc.
In order to deal with the "air killer" of particles, people think of forests. Studies have shown that forests have the function of "filters", which can remove particles in the air. Because the trees are lush, the dust retention area is large, and the branches and leaves have the opposite charge to the smoke, which can absorb floating dust. In addition, the high humidity in the forest increases the adhesion to particulate matter; Branches and dense branches and leaves can prevent strong winds from slowing down the wind speed, and also make particles difficult to be blown up. In addition, particles are condensation nuclei of raindrops, which fall to the ground with the rain. After the rain, the particulate matter in the atmosphere is greatly reduced, and the trees polluted by dust can recover their dust retention ability after being washed by rain. According to the measurement, 1 ha pine forest can remove 36 tons of particulate matter every year, and 1 mu forest belt can absorb and assimilate 1 00 tons of pollutants in1year; The dust absorption capacity of elm is as high as 3.39 g/m2. In addition, such as Populus tomentosa, Populus macrophylla, Paulownia, Amorpha fruticosa, Ligustrum lucidum, oleander and Platycladus orientalis are all good tree species for dust retention; Poplar and mulberry trees have the ability to absorb lead dust; Osmanthus fragrans, palm and wintersweet all have the ability to absorb mercury. No wonder people call the forest a "nemesis" for handing over air and dust.