Harmful air pollutants

chinacdc.cn | Updated: 2022-03-18
Air pollution refers to the phenomenon that pollutants reach a certain concentration in the atmosphere over a prolonged period due to human activities or natural processes. 
Pollution caused by natural processes includes sand, dust, sand storms, volcanic eruption and forest fires. Pollution can also be caused by peoples’ production and living activities, including stationary pollution sources (chimneys and industrial exhaust pipes) and mobile pollution sources (automobiles, trains, ships, airplanes and other vehicles using petrochemical fuel as energy). 
Different air pollutants cause different hazards to health

Sulfur dioxide (SO2)
SO2 in the air can severely irritate respiratory mucosa, causing acute and chronic inflammation of the respiratory tract and functional decline of the lungs. Particulate matter adsorbed with SO2 can cause bronchial asthma. SO2 in blood can break the combination of vitamin B1 and vitamin C in the body, affecting metabolism and growth. Besides, SO2 can form acid rain, which is harmful to health. 
Nitrogen dioxide (NO2)
NO2 can be easily inhaled into deep bronchioles of the respiratory tract. Long-time exposure to NO2 can cause pulmonary edema and even chronic obstructive pulmonary diseases (COPD) in severe cases. 
Studies have shown that the increased incidences of bronchitis symptoms in asthmatic children are associated with long-term NO2 exposure. 
Ozone (O3)
Too much O3 in the air will affect the respiratory system, causing asthma and reducing lung function. European studies have shown that for every 10μg/m3 increase in O3 exposure, the daily mortality rate will increase by 0.3 percent and incidents of heart diseases will increase by 0.4 percent.
Particulate matter floating in the air can not only harm the respiratory system but also cause cardiovascular diseases, pulmonary heart disease and cancers. Additionally, PM2.5 scatters and absorbs sunlight, which reduces the intensity of ultraviolet radiation reaching the ground with an indirect effect on health. 
The influence of particulate matter in the air on health is related to particle sizes, composition and concentration. Particulates with a particle size bigger than 10 μm do not easily enter the respiratory tract; those with a particle size between 5μm and 10μm are mostly deposited in the upper respiratory tract; those with a particle size between 2.5μm and 5μm are mostly deposited in the bronchioles and alveoli and 75 percent of particulates with a particle size smaller than 2.5μm are deposited in alveoli. 
Different components of PM2.5 have different effects on health. Fine particulate matter adsorbed with organic compounds can cause asthma or the symptoms of aggravated allergic rhinitis. The amount of polycyclic aromatic hydrocarbons (PAHs) in fine particulate matter determines its carcinogenic activity. Particulate matter with bacteria, virus and fungus can cause respiratory infectious diseases, and fine particulate matter adsorbed with harmful gas can cause irritation or corrode alveolar walls.