Air pollution refers to the presence of one or more pollutants in the air. The quantity, nature, and duration of air pollution can harm human and animal life, damage property, or disrupt a comfortable living environment, such as the presence of odors. In other words, any substance that has sufficient quantity, nature, and duration to impact humans, other organisms, or property can be considered an air pollutant, and the phenomenon caused by its presence is known as air pollution. That is to say, an abnormal increase in certain substances in the air can lead to air pollution. People need to breathe air to sustain life. An adult breathes approximately 20,000 times a day, inhaling about 15 to 20 cubic meters of air.

Air pollution has a direct impact on human health. The hazards of atmospheric pollutants to the human body manifest in various ways, including respiratory diseases, physiological dysfunction, and irritation to mucous membranes such as the eyes and nose. For example, during a smog incident in London, UK in December, 4,000 people died, including 1,952. This disaster was called the "killing smoke." Analysis suggests that this was due to a lack of wind and fog in London during those days. Factory chimney emissions, dust, and residents' heating were widespread in the city. The concentration of smoke particles reached 4.46mg/m³, and the average daily concentration of sulfur dioxide was 3.83ml/m³. Through chemical reactions, sulfur dioxide forms droplets of sulfuric acid that adhere to the smoke particles or condense on droplets, entering the organs with breathing, causing diseases or accelerating the death of chronic patients. This is what is known as photochemical pollution.

From the above examples, it can be seen that high levels of pollutants in the atmosphere can lead to acute pollution poisoning, worsen symptoms, and even cause the deaths of thousands of people within a few days. In fact, even when the concentration of pollutants in the atmosphere is not high, the human body can inhale years of polluted air, which can also lead to chronic bronchitis, bronchial asthma, emphysema, and lung cancer, among other diseases.