Air pollution caused by human beings goes hand in hand with civilization. Before
industrialization, pollution of the air one breathes was mainly due to the use of open
fireplaces, which emitted smoke, CO, CO, and gaseous organic combustion products,
and the formation of urban structures then gradually led to a significant deterioration
in the outdoor air quality in centres of population. The birth of the industrial era led
to important sources of emission of polluting substances in the indoor and outdoor
air, and reports of diseases caused by air pollution began to increase in number. Today,
most people living in modern industrial regions, particularly during the colder
months, spend 90 % of their time in closed rooms with only short airing periods.
Heat insulating measures significantly lowered the energy consumption in dwellings,
office-blocks and state-maintained buildings, but at the same time the fresh air supply
was drastically decreased, leading to an increased accumulation of emitted substances,
sometimes exceeding the values measured in outdoor air. Moreover, in the sixties and
seventies, materials containing unhealthy substances were used uncritically, creating
sources of long-term emission and, as a consequence, a clean-up requirement in
many buildings. Well-known examples are formaldehyde (emissions from wood-based
materials), pentachlorophenol and its water-soluble sodium salt (wood preservatives) and
polychlorinated biphenyls (insulating materials). In addition, many health problems are
caused by biological particles such as fungi, dander from pets, and bacteria.