Every year, the Barcelona Public Health Agency evaluates the concentration levels of other pollutants, such as ozone, sulphur dioxide, carbon monoxide, lead, cadmium, nickel, arsenic, benzo(a)pyrene and benzene.


Tropospheric and ground-level ozone

  • Ozone is a colourless oxidant gas that is produced by photochemical reactions between the nitrogen oxides present in atmospheric pollution and some volatile organic compounds. This should not be confused with ozone in the higher layers of the atmosphere which protects us from the sun’s UV radiation.
  • When the sunlight is more intense, the concentration increases.
  • The precursor gases are generated in Barcelona, but the wind blows the ozone towards regions in the north-west.


Sulphur dioxide (SO2)

  • A colourless gas that smells like burnt matches. In combination with water and oxygen, it forms acid rain.
  • It is mostly produced by power stations and other industrial activities.


Carbon monoxide (CO)

  • An insipid, colourless and odourless gas, which is therefore undetectable without measuring apparatus.
  • It is produced by vehicle exhausts and, to a lesser extent, by heating.


Volatile organic compounds (VOC)

  • Carbon-based molecules that are very volatile due to their tendency to evaporate into gases. For this reason, they can travel a long way from their point of emission.
  • They cause irritation and loss of pulmonary capacity. Some VOCs are classified as carcinogens.
  • They are produced by vehicles, industry and the use of solvents.


Carbon dioxide (CO2)

  • An insipid, colourless and odourless gas. It is not toxic and, therefore, it is not considered to be directly harmful to health. However, it is a greenhouse gas and has a direct effect on global warming and climate change.
  • It is produced by combustion in engines, heating, etc.