Nitrogen dioxide
Nitrogen dioxide, NO2, is a red-brown gas (visible in high concentrations) formed during combustion or oxidation of nitric oxide. Nitrogen dioxide irritates the respiratory tract and can cause damage to the lungs. In very high concentrations of nitrogen dioxide is lethal.
Nitrogen dioxide is one of the worst air pollution for two reasons. First, the gas itself is very irritating to the respiratory tract and contributes to the formation of ground-level ozone. In nature, seems to acidifying gas (lowers the pH of soil and water).
For most urban areas road traffic is the biggest source of emissions. Although the total emissions declined slightly since the 1980s, the emissions are still too high. Emissions from new vehicles is lower, but improvements "eaten up" by increased traffic.
Sulphur dioxide
Sulphur dioxide, SO2, is a colorless gas that can cause cough. The gas is produced naturally when organic material decomposes. It also occurs in the combustion of sulfur-containing substances, including fossil fuels. The largest natural source of sulfur dioxide is volcanoes. In nature, seems to acidifying gas (lowers the pH of soil and water).
In Sweden, the sulfur dioxide emissions have fallen sharply since the 1970s. The decrease is primarily improved gas in large combustion plants and a shift to low-sulfur oil. The replacement of coal and oil with biofuels has also reduced emissions.
Benzene
Benzene (ex benzene) is a colorless and flammable liquid with strong odor. Benzene is used in particular as a solvent for substances with a fat-like properties. Benzene has been shown to be carcinogenic and are therefore not used as a solvent to the same extent as before.
The main sources of benzene are motor vehicle emissions, evaporative losses during transportation, distribution and storage of petroleum products and the emissions from the burning of wood, especially in non-environmentally approved equipment.
Ozone
Ozone is the pure form an explosive gas, with a special scent that can be sensed by lightning. The formation of electrical discharges. Even in low concentrations is toxic. Ozone is used extensively for disinfection of drinking water and water for the brewing industry needs, for waste water treatment and bleaching of pulp.
Ground level ozone is formed by chemical reactions between nitrogen oxides and volatile organic compounds (VOCs). The concentrations are usually higher in spring and summer and in the afternoons, because the reaction accelerated in the presence of sunlight and high temperatures. Ozone concentrations may exhibit great variation depending on weather, season, time of day and changes in the amount of long-range transported ozone.
