First, the overall summary:

Air pollution is one of the most important environmental problems in the world at present. There are many kinds of pollutants, including particulate matter, sulfur oxides, carbon monoxide, nitrogen oxidants and photochemical oxidants. It will do great harm to human health, industrial and agricultural production, utensils and materials, animal and plant growth, social property and the global environment.

Second, the way of pollutants invading the human body:

The impact of air pollution is global, and the grim situation deserves extensive attention and active participation in improvement. There are three main ways for air pollutants to invade the human body: body surface contact, eating food and water containing pollutants, and inhaling polluted air, of which the third way is the most important. The harm of air pollution to human health is mainly manifested in respiratory diseases.

Iii. Sources of air pollution:

Air pollutants enter the atmosphere (input) from artificial or natural sources, participate in the circulation process of the atmosphere, and are removed (output) from the atmosphere through chemical reactions, biological activities and physical sedimentation after a certain retention time. If the output rate is less than the input rate, it will be relatively concentrated in the atmosphere, resulting in an increase in the concentration of a substance in the atmosphere.

Harm of air pollution to plants;

The harm of air pollution to plants usually occurs in the structure of leaves, because leaves contain the structural mechanism of the whole plant. Common gases that are toxic to plants are sulfur dioxide, ozone, polyacrylonitrile, hydrogen fluoride, ethylene, hydrogen chloride, chlorine, hydrogen sulfide and ammonia. Excessive SO2 in the atmosphere is harmful to leaves, firstly to spongy soft tissue of mesophyll, and secondly to palisade cells.

At the initial stage of erosion, the leaves were soaked in water, and after drying, the affected leaves were bleached or milky white. If the concentration of SO2 is (0.3 ~ 0.5) x 10-6 for several days, it will cause chronic damage to sensitive plants. SO2 directly enters the stomata, and the plant cells in mesophyll convert it into sulfite, and then into sulfate.

When excessive SO2 exists, plant cells can't convert sulfite into sulfate as soon as possible, and begin to destroy the cell structure. Spinach, lettuce and other leafy vegetables are most sensitive to SO2, and cotton and alfalfa are also sensitive. Pine needles are also affected by it, and both the needle tip and the whole needle will become brown and fragile.