The Air Pollution Index (API) is to simplify the concentration of several air pollutants that are routinely monitored into a single conceptual index value form, and to characterize the degree of air pollution and air quality in grades, which is suitable for expressing the short-term air of the city. Quality status and changing trends.

The air pollution index is based on the air environmental quality standards and the ecological environmental effects of various pollutants and their impact on human health to determine the grading value of the pollution index and the corresponding air pollutant concentration limit. The air pollution index used in the weekly air quality report The classification standards are:

1. The concentration of pollutants corresponding to an air pollution index (API) of 50 points is the national first-level standard for daily average air quality;

2. The pollution concentration corresponding to API 100 points is the national second-level standard for daily average air quality;

3. The pollutant concentration corresponding to API 200 points is the third-level national daily average air quality standard;

4. The classification of API higher value segment corresponds to the concentration limit when various pollutants have different effects on human health.

According to the characteristics of my country's air pollution and the focus of pollution prevention, the items currently included in the air pollution index are tentatively designated as: sulfur dioxide, nitrogen oxides and total suspended particulate matter.

The main pollutants in the air are sulfur dioxide, nitrogen oxides, particulate pollutants, and acid rain.

1. Sulfur dioxide (SO2)

Sulfur dioxide is mainly produced by burning coal and fuel oil and other sulfur-containing substances, followed by nature, such as volcanic eruptions and forest fires.

Sulfur dioxide has a strong irritation to the conjunctiva and upper respiratory mucosa of the human body. It can damage the respiratory tube and cause bronchitis, pneumonia, and even pulmonary edema, respiratory paralysis. The mortality of elderly or chronic patients who have short-term exposure to sulfur dioxide at a concentration of 0.5 mg/m3 of air increases, and the concentration higher than 0.25 mg/m3 can worsen the condition of patients with respiratory diseases. People who have long-term exposure to air at a concentration of 0.1 mg/m3 have increased respiratory disease. In addition, sulfur dioxide is easy to cause corrosion, peeling, fading and damage to metal materials, building construction, cotton spinning chemical fiber fabrics, leather and paper and other products. It can also make plant leaves turn yellow or even die. The national environmental quality standards stipulate that the daily average concentration in residential areas is less than 0.15 mg/m3, and the annual average concentration is less than 0.06 mg/m3.

2. Nitrogen oxides (NOx)

Nitrogen oxides in the air are nitrous oxide (N2O), nitric oxide (NO), nitrogen dioxide (NO2), nitrous oxide (N2O3), etc. The main components are nitric oxide and dioxide Nitrogen is expressed as NOx (nitrogen oxide). NOx pollution mainly comes from the combustion products of coal, petroleum and other fuels used in production and daily life (including the NOx emitted by the combustion of automobiles and all internal combustion engines); secondly, it comes from the exhaust emissions from factories that produce or use nitric acid. When NOx and hydrocarbons coexist in the air, they undergo a photochemical reaction when irradiated by the ultraviolet rays of the sun to produce a photochemical smog, which is a toxic secondary pollutant. NO2 is four times more toxic than NO and can cause lung damage and even pulmonary edema. Chronic poisoning can cause trachea and lung disease. Inhalation of NO can cause the formation of degenerated hemoglobin and affect the central nervous system. The concentration of NOx on animals is approximately 1.0 mg/m3, and the concentration of NOx on patients is approximately 0.2 mg/m3. The national environmental quality standards stipulate that the average concentration in residential areas is less than 0.10 mg/m3, and the annual average concentration is less than 0.05 mg/m3.

3. Particulate pollutants

The particulate pollutants in the air are large in number and complex in composition, and they can be toxic substances or carriers of other pollutants. It is mainly derived from soot discharged from the incomplete combustion of coal and other fuels, dust generated during industrial production, construction and traffic dust, wind dust, etc., and salt particles formed by physical and chemical reactions of gaseous pollutants. In air pollution monitoring, the monitoring items of particulate pollutants are mainly total suspended particulate matter, natural dust and floating dust.

(1) Total suspended particulate matter (TSP)

Total suspended particulates refer to particulates with a particle size below 100 microns, referred to as TSP. The degree of its harm to the human body is mainly determined by its own particle size and chemical composition. Almost all substances with a particle size greater than 10 microns in TSP can be trapped in the nasal cavity and throat and do not enter the alveoli. The most harmful to the human body is the floating particles below 10 microns, called floating dust. It can be deposited in the alveoli through the respiratory tract. The incidence of chronic respiratory tract inflammation, emphysema, and lung cancer is obviously related to the degree of air particulate pollution. When exposed to air with a particulate concentration higher than 0.2 mg/m3 for many years, the respiratory system diseases increase. The national environmental quality standards stipulate that the daily average concentration in residential areas is less than 0.3 mg/m3, and the annual average concentration is less than 0.2 mg/m3.

(2) Natural dust fall

Natural dust fall refers to the dust whose particle size is larger than 10 microns can settle on the ground by gravity in the air. Its source is mainly sand and dust. Inhalation of dust will increase the resistance of the respiratory tract, and the respiratory tract will become narrow.

4. Acid rain

When the pH value of precipitation is lower than 5.6, the precipitation is acid rain. The sulfur dioxide emitted by coal combustion and the nitrogen oxide emitted by motor vehicles are the main factors that form acid rain; secondly, meteorological conditions and topographical conditions are also important factors that affect the formation of acid rain. Precipitation acidity pH

5. Carbon monoxide (CO)

Carbon monoxide is a colorless and odorless gas. Mainly comes from the incomplete combustion of carbon-containing fuels and cigarettes, followed by industrial production processes such as coking, steelmaking, and ironmaking. Human body inhales carbon monoxide and easily combines with hemoglobin to produce carboxyhemoglobin, which reduces the oxygen-carrying capacity of the blood stream, resulting in weakened consciousness, weakened central nervous function, weakened heart and lung respiratory functions; the victim feels dizzy, headache, nausea, and fatigue Even died in a coma. my country's air environmental quality standards stipulate that the daily average concentration of carbon monoxide in residential areas is less than 4.00 mg/m3.

6. Fluoride (F)

Refers to inorganic fluorides that exist in gaseous and particulate forms. Mainly from the production of fluorine-containing products, phosphate fertilizer plants, steel plants, aluminum smelting plants and other industrial production processes. Fluoride has a strong irritation to the eyes and respiratory organs. Inhalation of high concentrations of fluoride gas can cause pulmonary edema and bronchitis. Long-term inhalation of low-concentration fluoride gas can cause chronic poisoning and skeletal fluorosis, reducing calcium in the bones, leading to bone sclerosis and osteoporosis. my country's ambient air quality standards stipulate that the average daily concentration in urban areas is 7 micrograms/m3.

7. Lead and its compounds (Pb)

Refers to lead and its compounds present in total suspended particles. Mainly comes from exhaust gas emitted by cars. Lead enters the human body, and most of it accumulates in human bones, damaging the skeletal hematopoietic system and nervous system, as well as the male gonads. The clinical symptoms are anemia, peripheral neuritis, movement and sensory abnormalities. In my country, 80 micrograms/liter of urine lead is the normal value, and normal blood lead is less than 50 micrograms/ml.

8. Mercury

Mercury (Hg) and its compounds are highly toxic substances and can accumulate in the body. The mercury in the air migrates into the water body after being leached and washed by rainwater. The main hazards of mercury in water to the human body are headache, dizziness, numbness and pain. The methylmercury in the total mercury is easily absorbed by the liver and kidneys in the human body, and only 15% of it is absorbed by the brain, but the first damage is the brain tissue, and it is difficult to treat, often leading to death or life-long suffering.