Air pollution is dominated by industrial and productive pollution, followed by domestic pollution and transportation pollution.
• Fuel combustion: The combustion of coal and petroleum discharges massive hazardous substances. Coal burning produces soot and sulfur dioxide, while oil combustion releases sulfur dioxide, carbon monoxide and other pollutants.
• Industrial waste gas: Waste gas and soot are emitted during industrial production. Thermal power plants, iron and steel plants, petrochemical plants and cement plants are major pollution contributors.
• Agricultural pollution: Ammonia volatilizes from applied chemical fertilizers and reacts with acidic substances to form ammonium salts, a key component of PM2.5. Open straw burning releases large quantities of PM2.5, carbon monoxide and polycyclic aromatic hydrocarbons. Pesticide spraying also generates airborne dust and droplets.
Coal combustion from household cooking stoves and heating boilers discharges soot, sulfur dioxide and other harmful gases.
Motor vehicles, trains, ships and aircraft all emit exhaust fumes. Vehicle exhaust is released close to human breathing zones and readily inhaled, containing nitrogen oxides, hydrocarbons, carbon monoxide, PM2.5 and PM10 particulate matter.
