Air pollutants

Clean, natural air is an indispensable necessity of life for plants, animals and human beings. However, what we breathe today is no longer clean air, but a somewhat contaminated mixture. Human beings release large quantities of gases, aerosols and dust particles into the atmosphere every year, especially through the combustion of fossil heating and motor fuels, in industrial processes and in agriculture. This panel of pollutants can lead to considerable and prolonged human exposures and pollution of the environment both near to and far from their place of release. [Source: FOEN]

The substitution of fossil (and more generally non-renewable) fuels and the reduction of greenhouse gas emissions are amongst the main reasons for introducing biofuels on the market today. Although the two aspects are of course essential, they must not however obscure the national targets for the reduction of air pollution. These objectives are largely related to the transportation sector.

Greenhouse gas (GHG) emissions by human beings are the main cause of the global warming phenomenon and rising temperatures worldwide. Since the beginning of the industrial age, there has been a significant increase in the concentration of GHG in the atmosphere. As a result, the concentration of CO2, the main GHG, increased by over 30%. In Switzerland, about 80% of GHG emissions emerge in the form of CO2 during the combustion of fossil fuels. The remaining 20% are distributed as follows:

• methane (CH4) : 7%
• dinitrogen oxide (N2O): 6%
• synthetic greenhouse gases (HFC, PFC, SF6): 1-2%
• carbon dioxide (CO2) from non-energy applications (mainly cement manufacturing) : 5%

Because the gases are acting directly on the greenhouse effect, they are subject to measures of climate policy. A number of trace gases with an indirect greenhouse effect (also referred to as precursors) must also be taken into consideration. These include carbon monoxide (CO), nitrogen oxides (NOx) and volatile organic compounds (VOCs without methane). These gases only slightly absorb infrared radiation, but they are active in the atmosphere and promote the formation of greenhouse gases such as methane (CH4), of which they also prolong the life.

Carbon monoxide (CO) is colourless and odourless gas, which acts as a respiratory poison in humans and warm-blooded animals. It is formed during incomplete combustion of heating and motor fuels (mainly road transport) and plays a role in the formation of ozone in the free troposphere.

Nitrogen oxides is a generic term including nitrogen dioxide (NO2) and nitrogen monoxide (NO). Because NO rapidly oxidizes to NO2, the emissions are expressed in terms of "nitrogen dioxide (NO2) equivalents". The main effects include respiratory disorders, significant damage to many plants and sensitive ecosystems through the combined action of several pollutants and overfertilization of ecosystems. Nitrogen oxides are important precursors for the formation of acid rain, secondary aerosols and - together with volatile organic compounds - photochemical oxidants (ozone/summer smog).

Sulphur dioxide (SO2) is a colorless gas, the smell of which becomes acrid under severe concentrations. It results mainly from the combustion of fuels containing sulphur. The sulphur content of vehicle fuels having significantly decreased in the past few years, the main sources of SO2 are today industrial and household heaters. The main effects include airway disorders, damage to many plants and sensitive ecosystem, and an erosion of buildings and materials. It is also an important precursor to the formation of acid rain.

Volatile organic compounds (VOCs) include a wide variety of pollutants usually divided into three categories depending on their specific effects, namely chlorofluorocarbon (CFCs), methane (CH4), and non-methane non-chlorofluorocarbon volatile organic compounds (NMVOCs). VOCs often refer to NMVOCs. The latter are mainly formed as a result of the evaporation of solvents and vehicle fuels and/or as a result of incomplete combustion (trade, industry, road transport). The effects can vary significantly, depending on the toxicity and carcinogenic nature of the compounds (e.g. benzene). Together with nitrogen oxides, VOCs are major precursors for the formation of photochemical oxidants (ozone/summer smog).

Tiny airborne dust particles represent one of the greatest challenges for today's air pollution control policy. People living in cities and/or near major traffic routes are particularly affected by high levels of particulate matter pollution. In these areas the annual average ambient air quality standard is exceeded, and the imission value for daily mean concentrations is also frequently exceeded, in some cases dramatically. The term PM10 is used to designate particles with a diameter measuring less than 10 micrometers, which can penetrate the finest branches of the bronchial tree and sometimes pass into the lymphatic system and the bloodstream. Because of their fissured structure, these particles offer an ideal surface for the attachment of other toxic substances. This cocktail of pollutants comprises a wide range of compounds, some of them carcinogenic. It causes local inflammation in the respiratory tract and may thus produce serious effects on health: cough, respiratory distress, bronchitis and asthma attacks in children and adults; respiratory and cardiovascular disease, possibly necessitating hospitalization; lung cancer; and premature deaths.

Ground-level ozone is a secondary pollutant which is formed in the troposphere from nitrogen oxides (NOx) and volatile organic compounds (VOCs) under the influence of sunlight. The main sources of precursor pollutants include transport and industry. Ozone irritates the respiratory mucosa, causes tightness of the chest, reduces lung function and is harmful to plants. In the lower air, ozone also acts as a greenhouse gas.